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Consciousness, at its simplest, is
awareness In philosophy and psychology, awareness is the perception or knowledge of something. The concept is often synonymous with consciousness. However, one can be aware of something without being explicitly conscious of it, such as in the case of bli ...
of a state or object, either internal to oneself or in one's external environment. However, its nature has led to millennia of analyses, explanations, and debate among philosophers, scientists, and theologians. Opinions differ about what exactly needs to be studied or even considered consciousness. In some explanations, it is synonymous with the
mind The mind is that which thinks, feels, perceives, imagines, remembers, and wills. It covers the totality of mental phenomena, including both conscious processes, through which an individual is aware of external and internal circumstances ...
, and at other times, an aspect of it. In the past, it was one's "inner life", the world of
introspection Introspection is the examination of one's own conscious thoughts and feelings. In psychology, the process of introspection relies on the observation of one's mental state, while in a spiritual context it may refer to the examination of one's s ...
, of private thought,
imagination Imagination is the production of sensations, feelings and thoughts informing oneself. These experiences can be re-creations of past experiences, such as vivid memories with imagined changes, or completely invented and possibly fantastic scenes ...
, and volition. Today, it often includes any kind of
cognition Cognition is the "mental action or process of acquiring knowledge and understanding through thought, experience, and the senses". It encompasses all aspects of intellectual functions and processes such as: perception, attention, thought, ...
,
experience Experience refers to Consciousness, conscious events in general, more specifically to perceptions, or to the practical knowledge and familiarity that is produced by these processes. Understood as a conscious event in the widest sense, experience i ...
, feeling, or
perception Perception () is the organization, identification, and interpretation of sensory information in order to represent and understand the presented information or environment. All perception involves signals that go through the nervous syste ...
. It may be awareness, awareness of awareness,
metacognition Metacognition is an awareness of one's thought processes and an understanding of the patterns behind them. The term comes from the root word ''Meta (prefix), meta'', meaning "beyond", or "on top of".Metcalfe, J., & Shimamura, A. P. (1994). ''Metac ...
, or
self-awareness In philosophy of self, philosophy, self-awareness is the awareness and reflection of one's own personality or individuality, including traits, feelings, and behaviors. It is not to be confused with consciousness in the sense of qualia. While ...
, either continuously changing or not. The disparate range of research, notions, and speculations raises a curiosity about whether the right questions are being asked. Examples of the range of descriptions, definitions or explanations are: ordered distinction between self and environment, simple
wakefulness Wakefulness is a daily recurring brain state and state of consciousness in which an individual is conscious and engages in coherent cognition, cognitive and behavioral responses to the external world. Being awake is the opposite of being asleep, ...
, one's sense of selfhood or
soul The soul is the purported Mind–body dualism, immaterial aspect or essence of a Outline of life forms, living being. It is typically believed to be Immortality, immortal and to exist apart from the material world. The three main theories that ...
explored by "looking within"; being a metaphorical "
stream A stream is a continuous body of water, body of surface water Current (stream), flowing within the stream bed, bed and bank (geography), banks of a channel (geography), channel. Depending on its location or certain characteristics, a strea ...
" of contents, or being a
mental state A mental state, or a mental property, is a state of mind of a person. Mental states comprise a diverse class, including perception, pain/pleasure experience, belief, desire, intention, emotion, and memory. There is controversy concerning the exact ...
,
mental event A mental event is any event that happens within the mind of a conscious individual. Examples include thoughts, feelings, decisions, dreams, and realizations. These events often make up the conscious life that are associated with cognitive functio ...
, or
mental process Cognition is the "mental action or process of acquiring knowledge and understanding through thought, experience, and the senses". It encompasses all aspects of intellectual functions and processes such as: perception, attention, thought, i ...
of the
brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...
.


Etymology

The words "conscious" and "consciousness" in the English language date to the 17th century, and the first recorded use of "conscious" as a simple adjective was applied figuratively to inanimate objects (''"the conscious Groves"'', 1643). It derived from the
Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...
''conscius'' (''con-'' "together" and ''scio'' "to know") which meant "knowing with" or "having joint or common knowledge with another", especially as in sharing a secret.
Thomas Hobbes Thomas Hobbes ( ; 5 April 1588 – 4 December 1679) was an English philosopher, best known for his 1651 book ''Leviathan (Hobbes book), Leviathan'', in which he expounds an influential formulation of social contract theory. He is considered t ...
in ''
Leviathan Leviathan ( ; ; ) is a sea serpent demon noted in theology and mythology. It is referenced in several books of the Hebrew Bible, including Psalms, the Book of Job, the Book of Isaiah, and the pseudepigraphical Book of Enoch. Leviathan is of ...
'' (1651) wrote: "Where two, or more men, know of one and the same fact, they are said to be Conscious of it one to another". There were also many occurrences in Latin writings of the phrase ''conscius sibi'', which translates literally as "knowing with oneself", or in other words "sharing knowledge with oneself about something". This phrase has the figurative sense of "knowing that one knows", which is something like the modern English word "conscious", but it was rendered into English as "conscious to oneself" or "conscious unto oneself". For example, Archbishop Ussher wrote in 1613 of "being so conscious unto myself of my great weakness". The Latin '' conscientia'', literally 'knowledge-with', first appears in Roman juridical texts by writers such as
Cicero Marcus Tullius Cicero ( ; ; 3 January 106 BC – 7 December 43 BC) was a Roman statesman, lawyer, scholar, philosopher, orator, writer and Academic skeptic, who tried to uphold optimate principles during the political crises tha ...
. It means a kind of shared knowledge with moral value, specifically what a witness knows of someone else's deeds. Although
René Descartes René Descartes ( , ; ; 31 March 1596 – 11 February 1650) was a French philosopher, scientist, and mathematician, widely considered a seminal figure in the emergence of modern philosophy and Modern science, science. Mathematics was paramou ...
(1596–1650), writing in Latin, is generally taken to be the first philosopher to use ''conscientia'' in a way less like the traditional meaning and more like the way modern English speakers would use "conscience", his meaning is nowhere defined. In ''Search after Truth'' (', Amsterdam 1701) he wrote the word with a gloss: ''conscientiâ, vel interno testimonio'' (translatable as "conscience, or internal testimony"). It might mean the knowledge of the value of one's own thoughts. The origin of the modern concept of consciousness is often attributed to
John Locke John Locke (; 29 August 1632 (Old Style and New Style dates, O.S.) – 28 October 1704 (Old Style and New Style dates, O.S.)) was an English philosopher and physician, widely regarded as one of the most influential of the Enlightenment thi ...
who defined the word in his ''
Essay Concerning Human Understanding ''An Essay Concerning Human Understanding'' is a work by John Locke concerning the foundation of human knowledge and understanding. It first appeared in 1689 (although dated 1690) with the printed title ''An Essay Concerning Humane Understand ...
'', published in 1690, as "the perception of what passes in a man's own mind". The essay strongly influenced 18th-century
British philosophy British philosophy refers to the philosophical tradition of the British people. "The native characteristics of British philosophy are these: common sense, dislike of complication, a strong preference for the concrete over the abstract and a certa ...
, and Locke's definition appeared in
Samuel Johnson Samuel Johnson ( – 13 December 1784), often called Dr Johnson, was an English writer who made lasting contributions as a poet, playwright, essayist, moralist, literary critic, sermonist, biographer, editor, and lexicographer. The ''Oxford ...
's celebrated ''
Dictionary A dictionary is a listing of lexemes from the lexicon of one or more specific languages, often arranged Alphabetical order, alphabetically (or by Semitic root, consonantal root for Semitic languages or radical-and-stroke sorting, radical an ...
'' (1755). The French term ''conscience'' is defined roughly like English "consciousness" in the 1753 volume of
Diderot Denis Diderot (; ; 5 October 171331 July 1784) was a French philosopher, art critic, and writer, best known for serving as co-founder, chief editor, and contributor to the along with Jean le Rond d'Alembert. He was a prominent figure during t ...
and
d'Alembert Jean-Baptiste le Rond d'Alembert ( ; ; 16 November 1717 – 29 October 1783) was a French mathematician, mechanics, mechanician, physicist, philosopher, and music theorist. Until 1759 he was, together with Denis Diderot, a co-editor of the ''E ...
's
Encyclopédie , better known as ''Encyclopédie'' (), was a general encyclopedia published in France between 1751 and 1772, with later supplements, revised editions, and translations. It had many writers, known as the Encyclopédistes. It was edited by Denis ...
as "the opinion or internal feeling that we ourselves have from what we do".


Problem of definition

Scholars are divided as to whether
Aristotle Aristotle (; 384–322 BC) was an Ancient Greek philosophy, Ancient Greek philosopher and polymath. His writings cover a broad range of subjects spanning the natural sciences, philosophy, linguistics, economics, politics, psychology, a ...
had a concept of consciousness. He does not use any single word or terminology that is clearly similar to the
phenomenon A phenomenon ( phenomena), sometimes spelled phaenomenon, is an observable Event (philosophy), event. The term came into its modern Philosophy, philosophical usage through Immanuel Kant, who contrasted it with the noumenon, which ''cannot'' be ...
or
concept A concept is an abstract idea that serves as a foundation for more concrete principles, thoughts, and beliefs. Concepts play an important role in all aspects of cognition. As such, concepts are studied within such disciplines as linguistics, ...
defined by John Locke. Victor Caston contends that Aristotle did have a concept more clearly similar to
perception Perception () is the organization, identification, and interpretation of sensory information in order to represent and understand the presented information or environment. All perception involves signals that go through the nervous syste ...
. Modern dictionary definitions of the word ''consciousness'' evolved over several centuries and reflect a range of seemingly related meanings, with some differences that have been controversial, such as the distinction between ''inward awareness'' and ''perception'' of the physical world, or the distinction between ''conscious'' and ''unconscious'', or the notion of a ''mental entity'' or ''mental activity'' that is not physical. The common-usage definitions of ''consciousness'' in ''
Webster's Third New International Dictionary ''Webster's Third New International Dictionary of the English Language, Unabridged'' (commonly known as ''Webster's Third'', or ''W3'') is an American English-language dictionary published in September 1961. It was edited by Philip Babcock Gove a ...
'' (1966) are as follows: #* ''awareness or perception of an inward psychological or spiritual fact; intuitively perceived knowledge of something in one's inner self'' #* ''inward awareness of an external object, state, or fact'' #* ''concerned awareness;'' INTEREST, CONCERN—''often used with an attributive noun .g. class consciousness' # ''the state or activity that is characterized by sensation, emotion, volition, or thought; mind in the broadest possible sense; something in nature that is distinguished from the physical'' # ''the totality in psychology of sensations, perceptions, ideas, attitudes, and
feelings According to the '' APA Dictionary of Psychology'', a feeling is "a self-contained phenomenal experience"; feelings are "subjective, evaluative, and independent of the sensations, thoughts, or images evoking them". The term ''feeling'' is closel ...
of which an individual or a group is aware at any given time or within a particular time span—''compare STREAM OF CONSCIOUSNESS # ''waking life (as that to which one returns after sleep, trance, fever) wherein all one's mental powers have returned . . .'' # ''the part of mental life or psychic content in psychoanalysis that is immediately available to the ego—''compare PRECONSCIOUS, UNCONSCIOUS The ''
Cambridge English Dictionary The ''Cambridge Advanced Learner's Dictionary'' (abbreviated ''CALD'') is a British dictionary of the English language. It was first published in 1995 under the title ''Cambridge International Dictionary of English'' by the Cambridge Univers ...
'' defines consciousness as "the state of being awake, thinking, and knowing what is happening around you", as well as "the state of understanding and realizing something". The '' Oxford Living Dictionary'' defines consciousness as " e state of being aware of and responsive to one's surroundings", " person's awareness or perception of something", and " e fact of awareness by the mind of itself and the world". Philosophers have attempted to clarify technical distinctions by using a
jargon Jargon, or technical language, is the specialized terminology associated with a particular field or area of activity. Jargon is normally employed in a particular Context (language use), communicative context and may not be well understood outside ...
of their own. The corresponding entry in the ''
Routledge Encyclopedia of Philosophy The ''Routledge Encyclopedia of Philosophy'' is an encyclopedia of philosophy edited by Edward Craig that was first published by Routledge in 1998. Originally published in both 10 volumes of print and as a CD-ROM, in 2002 it was made available on ...
'' (1998) reads: ;Consciousness:Philosophers have used the term ''consciousness'' for four main topics: knowledge in general, intentionality, introspection (and the knowledge it specifically generates) and phenomenal experience... Something within one's mind is 'introspectively conscious' just in case one introspects it (or is poised to do so). Introspection is often thought to deliver one's primary knowledge of one's mental life. An experience or other mental entity is 'phenomenally conscious' just in case there is 'something it is like' for one to have it. The clearest examples are: perceptual experience, such as tastings and seeings; bodily-sensational experiences, such as those of pains, tickles and itches; imaginative experiences, such as those of one's own actions or perceptions; and streams of thought, as in the experience of thinking 'in words' or 'in images'. Introspection and phenomenality seem independent, or dissociable, although this is controversial.


Traditional metaphors for mind

During the early 19th century, the emerging field of
geology Geology (). is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth ...
inspired a popular
metaphor A metaphor is a figure of speech that, for rhetorical effect, directly refers to one thing by mentioning another. It may provide, or obscure, clarity or identify hidden similarities between two different ideas. Metaphors are usually meant to cr ...
that the mind likewise had hidden layers "which recorded the past of the individual". By 1875, most psychologists believed that "consciousness was but a small part of mental life", and this idea underlies the goal of Freudian therapy, to expose the of the mind. Other metaphors from various sciences inspired other analyses of the mind, for example:
Johann Friedrich Herbart Johann Friedrich Herbart (; 4 May 1776 – 14 August 1841) was a German philosopher, psychologist and founder of pedagogy as an academic discipline. Herbart is now remembered amongst the post-Kantian philosophers mostly as making the greatest ...
described ideas as being attracted and repulsed like magnets;
John Stuart Mill John Stuart Mill (20 May 1806 – 7 May 1873) was an English philosopher, political economist, politician and civil servant. One of the most influential thinkers in the history of liberalism and social liberalism, he contributed widely to s ...
developed the idea of "mental chemistry" and "mental compounds", and Edward B. Titchener sought the "structure" of the mind by analyzing its "elements". The abstract idea of ''states of consciousness'' mirrored the concept of
states of matter In physics, a state of matter is one of the distinct forms in which matter can exist. Four states of matter are observable in everyday life: solid, liquid, gas, and plasma. Different states are distinguished by the ways the component parti ...
. In 1892,
William James William James (January 11, 1842 – August 26, 1910) was an American philosopher and psychologist. The first educator to offer a psychology course in the United States, he is considered to be one of the leading thinkers of the late 19th c ...
noted that the "ambiguous word 'content' has been recently invented instead of 'object'" and that the metaphor of mind as a seemed to minimize the dualistic problem of how "states of consciousness can " things, or objects; by 1899 psychologists were busily studying the "contents of conscious experience by
introspection Introspection is the examination of one's own conscious thoughts and feelings. In psychology, the process of introspection relies on the observation of one's mental state, while in a spiritual context it may refer to the examination of one's s ...
and
experiment An experiment is a procedure carried out to support or refute a hypothesis, or determine the efficacy or likelihood of something previously untried. Experiments provide insight into cause-and-effect by demonstrating what outcome occurs whe ...
". Another popular metaphor was James's doctrine of the
stream of consciousness In literary criticism, stream of consciousness is a narrative mode or method that attempts "to depict the multitudinous thoughts and feelings which pass through the mind" of a narrator. It is usually in the form of an interior monologue which ...
, with continuity, fringes, and transitions. James discussed the difficulties of describing and studying psychological phenomena, recognizing that commonly-used terminology was a necessary and acceptable starting point towards more precise, scientifically justified language. Prime examples were phrases like ''inner experience'' and ''personal consciousness'':


From introspection to awareness and experience

Prior to the 20th century, philosophers treated the phenomenon of consciousness as the "inner world fone's own mind", and
introspection Introspection is the examination of one's own conscious thoughts and feelings. In psychology, the process of introspection relies on the observation of one's mental state, while in a spiritual context it may refer to the examination of one's s ...
was the mind "attending to" itself, an activity seemingly distinct from that of perceiving the 'outer world' and its physical phenomena. In 1892
William James William James (January 11, 1842 – August 26, 1910) was an American philosopher and psychologist. The first educator to offer a psychology course in the United States, he is considered to be one of the leading thinkers of the late 19th c ...
noted the distinction along with doubts about the inward character of the mind: By the 1960s, for many philosophers and psychologists who talked about consciousness, the word no longer meant the 'inner world' but an indefinite, large category called ''
awareness In philosophy and psychology, awareness is the perception or knowledge of something. The concept is often synonymous with consciousness. However, one can be aware of something without being explicitly conscious of it, such as in the case of bli ...
'', as in the following example: Many philosophers and scientists have been unhappy about the difficulty of producing a definition that does not involve circularity or fuzziness. In The ''Macmillan Dictionary of Psychology'' (1989 edition), Stuart Sutherland emphasized external awareness, and expressed a skeptical attitude more than a definition: Using 'awareness', however, as a definition or synonym of consciousness is not a simple matter: In 1974, philosopher
Thomas Nagel Thomas Nagel (; born July 4, 1937) is an American philosopher. He is the University Professor of Philosophy and Law Emeritus at New York University, where he taught from 1980 until his retirement in 2016. His main areas of philosophical interest ...
used 'consciousness', 'conscious experience', 'subjective experience' and the 'subjective character of experience' as synonyms for something that "occurs at many levels of animal life ... lthoughit is difficult to say in general what provides evidence of it." Nagel's terminology also included what has been described as "the standard 'what it's like' locution"Levine, Joseph (2010). Review of Uriah Kriegel, Subjective Consciousness: A Self-Representational Theory. ''Notre Dame Philosophical Reviews'' 2010 (3). in reference to the impenetrable
subjectivity The distinction between subjectivity and objectivity is a basic idea of philosophy, particularly epistemology and metaphysics. Various understandings of this distinction have evolved through the work of countless philosophers over centuries. One b ...
of any organism's
experience Experience refers to Consciousness, conscious events in general, more specifically to perceptions, or to the practical knowledge and familiarity that is produced by these processes. Understood as a conscious event in the widest sense, experience i ...
which Nagel referred to as "inner life" without implying any kind of introspection. On Nagel's approach,
Peter Hacker Peter Michael Stephan Hacker (born 15 July 1939) is a British philosopher. His principal expertise is in the philosophy of mind, philosophy of language, and philosophical anthropology. He is known for his detailed exegesis and interpretatio ...
commented: "Consciousness, thus conceived, is extended to the whole domain of 'experience'—of 'Life' ." He regarded this as a "novel analysis of consciousness" and has been particularly critical of Nagel's terminology and its philosophical consequences. In 2002 he attacked Nagel's 'what it's like' phrase as "malconstructed" and meaningless English—it sounds as if it asks for an analogy, but does not—and he called Nagel's approach logically "misconceived" as a definition of consciousness. In 2012 Hacker went further and asserted that Nagel had "laid the groundwork for ... forty years of fresh confusion about consciousness" and that "the contemporary philosophical conception of consciousness that is embraced by the 'consciousness studies community' is incoherent".


Influence on research

Many philosophers have argued that consciousness is a unitary concept that is understood by the majority of people despite the difficulty philosophers have had defining it. The term 'subjective experience', following Nagel, is amibiguous, as philosophers seem to differ from non-philosophers in their intuitions about its meaning. Max Velmans proposed that the "everyday understanding of consciousness" uncontroversially "refers to experience itself rather than any particular thing that we observe or experience" and he added that consciousness "is hereforeexemplified by the things that we observe or experience", whether thoughts, feelings, or perceptions. Velmans noted however, as of 2009, that there was a deep level of "confusion and internal division" among experts about the phenomenon of consciousness, because researchers lacked "a sufficiently well-specified use of the term...to agree that they are investigating the same thing". He argued additionally that "pre-existing theoretical commitments" to competing explanations of consciousness might be a source of bias. Within the "modern consciousness studies" community the technical phrase 'phenomenal consciousness' is a common synonym for all forms of awareness, or simply '
experience Experience refers to Consciousness, conscious events in general, more specifically to perceptions, or to the practical knowledge and familiarity that is produced by these processes. Understood as a conscious event in the widest sense, experience i ...
', without differentiating between inner and outer, or between higher and lower types. With advances in brain research, "the presence or absence of ''experienced phenomena''" of any kind underlies the work of those
neuroscientist A neuroscientist (or neurobiologist) is a scientist specializing in neuroscience that deals with the anatomy and function of neurons, Biological neural network, neural circuits, and glia, and their Behavior, behavioral, biological, and psycholo ...
s who seek "to analyze the precise relation of conscious phenomenology to its associated information processing" in the brain. This neuroscientific goal is to find the "neural correlates of consciousness" (NCC). One criticism of this goal is that it begins with a theoretical commitment to the neurological origin of all "experienced phenomena" whether inner or outer. Also, the fact that the easiest 'content of consciousness' to be so analyzed is "the experienced three-dimensional world (the phenomenal world) beyond the body surface" invites another criticism, that most consciousness research since the 1990s, perhaps because of bias, has focused on processes of external perception. From a
history of psychology Psychology is defined as "the scientific study of behavior and mental processes". Philosophical interest in the human mind and behavior dates back to the ancient civilizations of Egypt, Persia, Greece, China, and India. Psychology as a field of ...
perspective,
Julian Jaynes Julian Jaynes (February 27, 1920 – November 21, 1997) was an American psychologist who worked at the universities of Yale and Princeton for nearly 25 years and became best known for his 1976 book '' The Origin of Consciousness in the Break ...
rejected popular but "superficial views of consciousness" especially those which equate it with "that vaguest of terms,
experience Experience refers to Consciousness, conscious events in general, more specifically to perceptions, or to the practical knowledge and familiarity that is produced by these processes. Understood as a conscious event in the widest sense, experience i ...
". In 1976 he insisted that if not for
introspection Introspection is the examination of one's own conscious thoughts and feelings. In psychology, the process of introspection relies on the observation of one's mental state, while in a spiritual context it may refer to the examination of one's s ...
, which for decades had been ignored or taken for granted rather than explained, there could be no "conception of what consciousness is" and in 1990, he reaffirmed the traditional idea of the phenomenon called 'consciousness', writing that "its denotative definition is, as it was for René Descartes, John Locke, and
David Hume David Hume (; born David Home; – 25 August 1776) was a Scottish philosopher, historian, economist, and essayist who was best known for his highly influential system of empiricism, philosophical scepticism and metaphysical naturalism. Beg ...
, what is introspectable". Jaynes saw consciousness as an important but small part of human mentality, and he asserted: "there can be no progress in the science of consciousness until ... what is introspectable ssharply distinguished" from the processes of
cognition Cognition is the "mental action or process of acquiring knowledge and understanding through thought, experience, and the senses". It encompasses all aspects of intellectual functions and processes such as: perception, attention, thought, ...
such as
perception Perception () is the organization, identification, and interpretation of sensory information in order to represent and understand the presented information or environment. All perception involves signals that go through the nervous syste ...
, reactive
awareness In philosophy and psychology, awareness is the perception or knowledge of something. The concept is often synonymous with consciousness. However, one can be aware of something without being explicitly conscious of it, such as in the case of bli ...
and
attention Attention or focus, is the concentration of awareness on some phenomenon to the exclusion of other stimuli. It is the selective concentration on discrete information, either subjectively or objectively. William James (1890) wrote that "Atte ...
, and automatic forms of
learning Learning is the process of acquiring new understanding, knowledge, behaviors, skills, value (personal and cultural), values, Attitude (psychology), attitudes, and preferences. The ability to learn is possessed by humans, non-human animals, and ...
,
problem-solving Problem solving is the process of achieving a goal by overcoming obstacles, a frequent part of most activities. Problems in need of solutions range from simple personal tasks (e.g. how to turn on an appliance) to complex issues in business an ...
, and
decision-making In psychology, decision-making (also spelled decision making and decisionmaking) is regarded as the Cognition, cognitive process resulting in the selection of a belief or a course of action among several possible alternative options. It could be ...
. The
cognitive science Cognitive science is the interdisciplinary, scientific study of the mind and its processes. It examines the nature, the tasks, and the functions of cognition (in a broad sense). Mental faculties of concern to cognitive scientists include percep ...
point of view—with an inter-disciplinary perspective involving fields such as
psychology Psychology is the scientific study of mind and behavior. Its subject matter includes the behavior of humans and nonhumans, both consciousness, conscious and Unconscious mind, unconscious phenomena, and mental processes such as thoughts, feel ...
,
linguistics Linguistics is the scientific study of language. The areas of linguistic analysis are syntax (rules governing the structure of sentences), semantics (meaning), Morphology (linguistics), morphology (structure of words), phonetics (speech sounds ...
and
anthropology Anthropology is the scientific study of humanity, concerned with human behavior, human biology, cultures, society, societies, and linguistics, in both the present and past, including archaic humans. Social anthropology studies patterns of behav ...
—requires no agreed definition of "consciousness" but studies the interaction of many processes besides perception. For some researchers, consciousness is linked to some kind of "selfhood", for example to certain pragmatic issues such as the feeling of agency and the effects of regret and action on experience of one's own body or social identity. Similarly
Daniel Kahneman Daniel Kahneman (; ; March 5, 1934 – March 27, 2024) was an Israeli-American psychologist best known for his work on the psychology of judgment and decision-making as well as behavioral economics, for which he was awarded the 2002 Nobel Memor ...
, who focused on systematic errors in perception, memory and decision-making, has differentiated between two kinds of mental processes, or cognitive "systems": the "fast" activities that are primary, automatic and "cannot be turned off", and the "slow", deliberate, effortful activities of a secondary system "often associated with the subjective experience of agency, choice, and concentration". Kahneman's two systems have been described as "roughly corresponding to unconscious and conscious processes". The two systems can interact, for example in sharing the control of attention. While System 1 can be impulsive, "System 2 is in charge of self-control", and "When we think of ourselves, we identify with System 2, the conscious, reasoning self that has beliefs, makes choices, and decides what to think about and what to do". Some have argued that we should eliminate the concept from our understanding of the mind, a position known as consciousness semanticism. In
medicine Medicine is the science and Praxis (process), practice of caring for patients, managing the Medical diagnosis, diagnosis, prognosis, Preventive medicine, prevention, therapy, treatment, Palliative care, palliation of their injury or disease, ...
, a "level of consciousness" terminology is used to describe a patient's
arousal Arousal is the physiology, physiological and psychology, psychological state of being awoken or of Five senses, sense organs stimulated to a point of perception. It involves activation of the ascending reticular activating system (ARAS) in the hu ...
and responsiveness, which can be seen as a continuum of states ranging from full alertness and comprehension, through disorientation,
delirium Delirium (formerly acute confusional state, an ambiguous term that is now discouraged) is a specific state of acute confusion attributable to the direct physiological consequence of a medical condition, effects of a psychoactive substance, or ...
, loss of meaningful communication, and finally loss of movement in response to painful
stimuli A stimulus is something that causes a physiological response. It may refer to: *Stimulation **Stimulus (physiology), something external that influences an activity **Stimulus (psychology), a concept in behaviorism and perception *Stimulus (economi ...
. Issues of practical concern include how the level of consciousness can be assessed in severely ill, comatose, or anesthetized people, and how to treat conditions in which consciousness is impaired or disrupted. The degree or level of consciousness is measured by standardized behavior observation scales such as the Glasgow Coma Scale.


Philosophy of mind

While historically philosophers have defended various views on consciousness, surveys indicate that
physicalism In philosophy, physicalism is the view that "everything is physical", that there is "nothing over and above" the physical, or that everything supervenience, supervenes on the physical. It is opposed to idealism, according to which the world arises ...
is now the dominant position among contemporary philosophers of mind. For an overview of the field, approaches often include both historical perspectives (e.g., Descartes, Locke,
Kant Immanuel Kant (born Emanuel Kant; 22 April 1724 – 12 February 1804) was a German philosopher and one of the central Enlightenment thinkers. Born in Königsberg, Kant's comprehensive and systematic works in epistemology, metaphysics, et ...
) and organization by key issues in contemporary debates. An alternative is to focus primarily on current philosophical stances and empirical findings.


Coherence of the concept

Philosophers differ from non-philosophers in their intuitions about what consciousness is. While most people have a strong intuition for the existence of what they refer to as consciousness, skeptics argue that this intuition is too narrow, either because the concept of consciousness is embedded in our intuitions, or because we all are illusions.
Gilbert Ryle Gilbert Ryle (19 August 1900 – 6 October 1976) was a British philosopher, principally known for his critique of Cartesian dualism, for which he coined the phrase " ghost in the machine". Some of Ryle's ideas in philosophy of mind have been ca ...
, for example, argued that traditional understanding of consciousness depends on a Cartesian dualist outlook that improperly distinguishes between mind and body, or between mind and world. He proposed that we speak not of minds, bodies, and the world, but of entities, or identities, acting in the world. Thus, by speaking of "consciousness" we end up leading ourselves by thinking that there is any sort of thing as consciousness separated from behavioral and linguistic understandings.


Types

Ned Block Ned Joel Block (born 1942) is an American philosopher working in philosophy of mind who has made important contributions to the understanding of consciousness and the philosophy of cognitive science. He has been professor of philosophy and psychol ...
argues that discussions on consciousness have often failed properly to distinguish ''phenomenal consciousness'' from ''access consciousness''. The terms had been used before Block used them, but he adopted the short forms P-consciousness and A-consciousness. Pages 230 and 231 i
the version on the author's own website
According to Block: * P-consciousness is raw experience: it is moving, colored forms, sounds, sensations, emotions and feelings with our bodies and responses at the center. These experiences, considered independently of any impact on behavior, are called
qualia In philosophy of mind, qualia (; singular: quale ) are defined as instances of subjective, conscious experience. The term ''qualia'' derives from the Latin neuter plural form (''qualia'') of the Latin adjective '' quālis'' () meaning "of what ...
. * A-consciousness is the phenomenon whereby information in our minds is accessible for verbal report, reasoning, and the control of behavior. So, when we
perceive Perception () is the organization, identification, and interpretation of sensory information in order to represent and understand the presented information or environment. All perception involves signals that go through the nervous syste ...
, information about what we perceive is access conscious; when we introspect, information about our thoughts is access conscious; when we
remember Remember may refer to: Film and television Film * ''Remember'' (1926 film), an American silent drama film * ''Remember?'' (1939 film), an American romantic comedy * ''Remember'' (2015 film), a Canadian film by Atom Egoyan * ''Remember?'' (201 ...
, information about the past is access conscious, and so on. Block adds that P-consciousness does not allow of easy definition: he admits that he "cannot define P-consciousness in any remotely noncircular way. Although some philosophers, such as
Daniel Dennett Daniel Clement Dennett III (March 28, 1942 – April 19, 2024) was an American philosopher and cognitive scientist. His research centered on the philosophy of mind, the philosophy of science, and the philosophy of biology, particularly as those ...
, have disputed the validity of this distinction, others have broadly accepted it.
David Chalmers David John Chalmers (; born 20 April 1966) is an Australian philosopher and cognitive scientist, specializing in philosophy of mind and philosophy of language. He is a professor of philosophy and neural science at New York University, as well ...
has argued that A-consciousness can in principle be understood in mechanistic terms, but that understanding P-consciousness is much more challenging: he calls this the
hard problem of consciousness In the philosophy of mind, the hard problem of consciousness is to explain why and how humans and other organisms have qualia, phenomenal consciousness, or subjective experience. It is contrasted with the "easy problems" of explaining why and how ...
. Some philosophers believe that Block's two types of consciousness are not the end of the story.
William Lycan William G. Lycan ( ; born September 26, 1945) is an American philosopher and professor emeritus at University of North Carolina at Chapel Hill, where he was formerly the William Rand Kenan, Jr. Distinguished Professor. Since 2011, Lycan is also d ...
, for example, argued in his book ''Consciousness and Experience'' that at least eight clearly distinct types of consciousness can be identified (organism consciousness; control consciousness; consciousness ''of''; state/event consciousness; reportability; introspective consciousness; subjective consciousness; self-consciousness)—and that even this list omits several more obscure forms. There is also debate over whether or not A-consciousness and P-consciousness always coexist or if they can exist separately. Although P-consciousness without A-consciousness is more widely accepted, there have been some hypothetical examples of A without P. Block, for instance, suggests the case of a "
zombie A zombie (Haitian French: ; ; Kikongo: ''zumbi'') is a mythological undead corporeal revenant created through the reanimation of a corpse. In modern popular culture, zombies appear in horror genre works. The term comes from Haitian folkl ...
" that is computationally identical to a person but without any subjectivity. However, he remains somewhat skeptical concluding "I don't know whether there are any actual cases of A-consciousness without P-consciousness, but I hope I have illustrated their conceptual possibility".


Distinguishing consciousness from its contents

Sam Harris Samuel Benjamin Harris (born April 9, 1967) is an American philosopher, neuroscientist, author, and podcast host. His work touches on a range of topics, including rationality, religion, ethics, free will, determinism, neuroscience, meditation ...
observes: "At the level of your experience, you are not a body of cells, organelles, and atoms; you are consciousness and its ever-changing contents". Seen in this way, consciousness is a subjectively experienced, ever-present field in which things (the contents of consciousness) come and go. Christopher Tricker argues that this field of consciousness is symbolized by the mythical bird that opens the Daoist classic the ''Zhuangzi.'' This bird's name is Of a Flock ( ''peng'' 鵬), yet its back is countless thousands of miles across and its wings are like clouds arcing across the heavens. "Like Of a Flock, whose wings arc across the heavens, the wings of your consciousness span to the horizon. At the same time, the wings of every other being's consciousness span to the horizon. You are of a flock, one bird among kin."


Mind–body problem

Mental processes (such as consciousness) and physical processes (such as brain events) seem to be correlated, however the specific nature of the connection is unknown. The first influential philosopher to discuss this question specifically was Descartes, and the answer he gave is known as
mind–body dualism In the philosophy of mind, mind–body dualism denotes either that mental phenomena are non-physical, Hart, W. D. 1996. "Dualism." pp. 265–267 in ''A Companion to the Philosophy of Mind'', edited by S. Guttenplan. Oxford: Blackwell. or t ...
. Descartes proposed that consciousness resides within an immaterial domain he called '' res cogitans'' (the realm of thought), in contrast to the domain of material things, which he called ''
res extensa ''Res extensa'' is one of the two substances described by René Descartes in his Cartesian ontology (often referred to as "radical dualism"), alongside '' res cogitans''. Translated from Latin, "''res extensa''" means "extended thing" while th ...
'' (the realm of extension). He suggested that the interaction between these two domains occurs inside the brain, perhaps in a small midline structure called the
pineal gland The pineal gland (also known as the pineal body or epiphysis cerebri) is a small endocrine gland in the brain of most vertebrates. It produces melatonin, a serotonin-derived hormone, which modulates sleep, sleep patterns following the diurnal c ...
. Although it is widely accepted that Descartes explained the problem cogently, few later philosophers have been happy with his solution, and his ideas about the pineal gland have especially been ridiculed. However, no alternative solution has gained general acceptance. Proposed solutions can be divided broadly into two categories: dualist solutions that maintain Descartes's rigid distinction between the realm of consciousness and the realm of matter but give different answers for how the two realms relate to each other; and
monist Monism attributes oneness or singleness () to a concept, such as to existence. Various kinds of monism can be distinguished: * Priority monism states that all existing things go back to a source that is distinct from them; e.g., in Neoplatonis ...
solutions that maintain that there is really only one realm of being, of which consciousness and matter are both aspects. Each of these categories itself contains numerous variants. The two main types of dualism are
substance dualism Substance may refer to: * Matter, anything that has mass and takes up space Chemistry * Chemical substance, a material with a definite chemical composition * Drug, a chemical agent affecting an organism Arts, entertainment, and media Music * ' ...
(which holds that the mind is formed of a distinct type of substance not governed by the laws of physics), and
property dualism Property dualism describes a category of positions in the philosophy of mind which hold that, although the world is composed of just one kind of Substance theory, substance—Materialism, the physical kind—there exist two distinct kinds of pro ...
(which holds that the laws of physics are universally valid but cannot be used to explain the mind). The three main types of
monism Monism attributes oneness or singleness () to a concept, such as to existence. Various kinds of monism can be distinguished: * Priority monism states that all existing things go back to a source that is distinct from them; e.g., in Neoplatonis ...
are physicalism (which holds that the mind is made out of matter),
idealism Idealism in philosophy, also known as philosophical realism or metaphysical idealism, is the set of metaphysics, metaphysical perspectives asserting that, most fundamentally, reality is equivalent to mind, Spirit (vital essence), spirit, or ...
(which holds that only thought or experience truly exists, and matter is merely an illusion), and
neutral monism Neutral monism is an umbrella term for a class of metaphysical theories in the philosophy of mind, concerning the relation of mind to matter. These theories take the fundamental nature of reality to be neither mental nor physical; in other words i ...
(which holds that both mind and matter are aspects of a distinct essence that is itself identical to neither of them). There are also, however, a large number of idiosyncratic theories that cannot cleanly be assigned to any of these schools of thought. Since the dawn of Newtonian science with its vision of simple mechanical principles governing the entire universe, some philosophers have been tempted by the idea that consciousness could be explained in purely physical terms. The first influential writer to propose such an idea explicitly was
Julien Offray de La Mettrie Julien Offray de La Mettrie (; November 23, 1709 – November 11, 1751) was a French physician and philosopher, and one of the earliest of the French materialists of the Enlightenment. He is best known for his 1747 work '' L'homme machine'' ('' ...
, in his book '' Man a Machine'' (''L'homme machine''). His arguments, however, were very abstract. The most influential modern physical theories of consciousness are based on
psychology Psychology is the scientific study of mind and behavior. Its subject matter includes the behavior of humans and nonhumans, both consciousness, conscious and Unconscious mind, unconscious phenomena, and mental processes such as thoughts, feel ...
and
neuroscience Neuroscience is the scientific study of the nervous system (the brain, spinal cord, and peripheral nervous system), its functions, and its disorders. It is a multidisciplinary science that combines physiology, anatomy, molecular biology, ...
. Theories proposed by neuroscientists such as Gerald Edelman and
Antonio Damasio Antonio Damasio (; born 25 February 1944) is a Portuguese neuroscientist. He is currently the David Dornsife Chair in Neuroscience, as well as Professor of Psychology, Philosophy, and Neurology, at the University of Southern California, and, add ...
, and by philosophers such as Daniel Dennett, seek to explain consciousness in terms of neural events occurring within the brain. Many other neuroscientists, such as
Christof Koch Christof Koch ( ; born November 13, 1956) is an American cognitive scientist, neurophysiologist and computational neuroscientist best known for his work on the neural basis of consciousness. He was the president and chief scientist of the All ...
, have explored the neural basis of consciousness without attempting to frame all-encompassing global theories. At the same time,
computer scientist A computer scientist is a scientist who specializes in the academic study of computer science. Computer scientists typically work on the theoretical side of computation. Although computer scientists can also focus their work and research on ...
s working in the field of
artificial intelligence Artificial intelligence (AI) is the capability of computer, computational systems to perform tasks typically associated with human intelligence, such as learning, reasoning, problem-solving, perception, and decision-making. It is a field of re ...
have pursued the goal of creating digital computer programs that can simulate or embody consciousness. A few theoretical physicists have argued that classical physics is intrinsically incapable of explaining the holistic aspects of consciousness, but that quantum theory may provide the missing ingredients. Several theorists have therefore proposed quantum mind (QM) theories of consciousness. Notable theories falling into this category include the holonomic brain theory of Karl Pribram and
David Bohm David Joseph Bohm (; 20 December 1917 – 27 October 1992) was an American scientist who has been described as one of the most significant Theoretical physics, theoretical physicists of the 20th centuryDavid Peat Who's Afraid of Schrödinger' ...
, and the Orch-OR theory formulated by Stuart Hameroff and
Roger Penrose Sir Roger Penrose (born 8 August 1931) is an English mathematician, mathematical physicist, Philosophy of science, philosopher of science and Nobel Prize in Physics, Nobel Laureate in Physics. He is Emeritus Rouse Ball Professor of Mathematics i ...
. Some of these QM theories offer descriptions of phenomenal consciousness, as well as QM interpretations of access consciousness. None of the quantum mechanical theories have been confirmed by experiment. Recent publications by G. Guerreshi, J. Cia, S. Popescu, and H. Briegel could falsify proposals such as those of Hameroff, which rely on
quantum entanglement Quantum entanglement is the phenomenon where the quantum state of each Subatomic particle, particle in a group cannot be described independently of the state of the others, even when the particles are separated by a large distance. The topic o ...
in protein. At the present time many scientists and philosophers consider the arguments for an important role of quantum phenomena to be unconvincing. Empirical evidence is against the notion of quantum consciousness, an experiment about wave function collapse led by Catalina Curceanu in 2022 suggests that quantum consciousness, as suggested by
Roger Penrose Sir Roger Penrose (born 8 August 1931) is an English mathematician, mathematical physicist, Philosophy of science, philosopher of science and Nobel Prize in Physics, Nobel Laureate in Physics. He is Emeritus Rouse Ball Professor of Mathematics i ...
and Stuart Hameroff, is highly implausible. Apart from the general question of the "hard problem" of consciousness (which is, roughly speaking, the question of how mental experience can arise from a physical basis), a more specialized question is how to square the subjective notion that we are in control of our decisions (at least in some small measure) with the customary view of causality that subsequent events are caused by prior events. The topic of
free will Free will is generally understood as the capacity or ability of people to (a) choice, choose between different possible courses of Action (philosophy), action, (b) exercise control over their actions in a way that is necessary for moral respon ...
is the philosophical and scientific examination of this conundrum.


Problem of other minds

Many philosophers consider experience to be the essence of consciousness, and believe that experience can only fully be known from the inside, subjectively. The
problem of other minds The problem of other minds is a Philosophy, philosophical problem traditionally stated as the following Epistemology, epistemological question: "Given that I can only observe the behavior of others, how can I know that others have minds?" The pr ...
is a philosophical problem traditionally stated as the following
epistemological Epistemology is the branch of philosophy that examines the nature, origin, and limits of knowledge. Also called "the theory of knowledge", it explores different types of knowledge, such as propositional knowledge about facts, practical knowled ...
question: Given that I can only observe the behavior of others, how can I know that others have minds? The problem of other minds is particularly acute for people who believe in the possibility of
philosophical zombie A philosophical zombie (or "p-zombie") is a being in a thought experiment in the philosophy of mind that is physically identical to a normal human being but does not have conscious experience. For example, if a philosophical zombie were poked ...
s, that is, people who think it is possible in principle to have an entity that is physically indistinguishable from a human being and behaves like a human being in every way but nevertheless lacks consciousness. Related issues have also been studied extensively by Greg Littmann of the University of Illinois,''The Culture and Philosophy of Ridley Scott'', Greg Littmann, pp. 133–144, Lexington Books (2013). and by Colin Allen (a professor at the University of Pittsburgh) regarding the literature and research studying
artificial intelligence Artificial intelligence (AI) is the capability of computer, computational systems to perform tasks typically associated with human intelligence, such as learning, reasoning, problem-solving, perception, and decision-making. It is a field of re ...
in androids.''Moral Machines'', Wendell Wallach and Colin Allen, 288 pages, Oxford University Press, USA (June 3, 2010), . The most commonly given answer is that we attribute consciousness to other people because we see that they resemble us in appearance and behavior; we reason that if they look like us and act like us, they must be like us in other ways, including having experiences of the sort that we do. There are, however, a variety of problems with that explanation. For one thing, it seems to violate the
principle of parsimony In philosophy, Occam's razor (also spelled Ockham's razor or Ocham's razor; ) is the problem-solving principle that recommends searching for explanations constructed with the smallest possible set of elements. It is also known as the principle o ...
, by postulating an invisible entity that is not necessary to explain what we observe. Some philosophers, such as Daniel Dennett in a research paper titled "The Unimagined Preposterousness of Zombies", argue that people who give this explanation do not really understand what they are saying. More broadly, philosophers who do not accept the possibility of zombies generally believe that consciousness is reflected in behavior (including verbal behavior), and that we attribute consciousness on the basis of behavior. A more straightforward way of saying this is that we attribute experiences to people because of what they can ''do'', including the fact that they can tell us about their experiences.


Qualia

The term "qualia" was introduced in philosophical literature by C. I. Lewis. The word is derived from Latin and means "of what sort". It is basically a quantity or property of something as perceived or experienced by an individual, like the scent of rose, the taste of wine, or the pain of a headache. They are difficult to articulate or describe. The philosopher and scientist
Daniel Dennett Daniel Clement Dennett III (March 28, 1942 – April 19, 2024) was an American philosopher and cognitive scientist. His research centered on the philosophy of mind, the philosophy of science, and the philosophy of biology, particularly as those ...
describes them as "the way things seem to us", while philosopher and cognitive scientist
David Chalmers David John Chalmers (; born 20 April 1966) is an Australian philosopher and cognitive scientist, specializing in philosophy of mind and philosophy of language. He is a professor of philosophy and neural science at New York University, as well ...
expanded on qualia as the "
hard problem of consciousness In the philosophy of mind, the hard problem of consciousness is to explain why and how humans and other organisms have qualia, phenomenal consciousness, or subjective experience. It is contrasted with the "easy problems" of explaining why and how ...
" in the 1990s. When qualia is experienced, activity is simulated in the brain, and these processes are called
neural correlates of consciousness The neural correlates of consciousness (NCC) are the minimal set of neuronal events and mechanisms sufficient for the occurrence of the mental states to which they are related. Neuroscientists use empirical approaches to discover neural correla ...
(NCCs). Many scientific studies have been done to attempt to link particular brain regions with emotions or experiences. Species which experience qualia are said to have
sentience Sentience is the ability to experience feelings and sensations. It may not necessarily imply higher cognitive functions such as awareness, reasoning, or complex thought processes. Some writers define sentience exclusively as the capacity for ''v ...
, which is central to the
animal rights movement The animal rights movement, sometimes called the animal liberation, animal personhood, or animal advocacy movement, is a social movement that advocates an end to the rigid moral and legal distinction drawn between human and non-human animals, ...
, because it includes the ability to experience pain and suffering.


Identity

An unsolved problem in the philosophy of consciousness is how it relates to the nature of personal identity. This includes questions regarding whether someone is the "same person" from moment to moment. If that is the case, another question is what exactly the "identity carrier" is that makes a conscious being "the same" being from one moment to the next. The problem of determining personal identity also includes questions such as Benj Hellie's
vertiginous question Benj Hellie's vertiginous question asks why, of all the subjects of experience out there, ''this'' one—the one corresponding to the human being referred to as Benj Hellie—is the one whose experiences are ''lived''? (The reader is supposed to ...
, which can be summarized as "Why am I me and not someone else?". The philosophical problems regarding the nature of personal identity have been extensively discussed by Thomas Nagel in his book '' The View from Nowhere''. A common view of personal identity is that an individual has a continuous identity that persists from moment to moment, with an individual having a continuous identity consisting of a line segment stretching across time from birth to death. In the case of an afterlife as described in Abrahamic religions, one's personal identity is believed to stretch infinitely into the future, forming a ray or line. This notion of identity is similar to the form of dualism advocated by René Descartes. However, some philosophers argue that this common notion of personal identity is unfounded. Daniel Kolak has argued extensively against it in his book ''I am You''. Kolak refers to the aforementioned notion of personal identity being linear as "Closed individualism". Another view of personal identity according to Kolak is "Empty individualism", in which one's personal identity only exists for a single moment of time. However, Kolak advocates for a view of personal identity called
Open individualism Open individualism is a view within the philosophy of self, according to which there exists only one numerically identical subject, who is everyone at all times; in the past, present and future. It is a theoretical solution to the question of ...
, in which all consciousness is in reality a single being and individual personal identity in reality does not exist at all. Another philosopher who has contested the notion of personal identity is
Derek Parfit Derek Antony Parfit (; 11 December 1942 – 2 January 2017) was a British philosopher who specialised in personal identity, rationality, and ethics. He is widely considered one of the most important and influential moral philosophers of the lat ...
. In his book ''
Reasons and Persons ''Reasons and Persons'' is a 1984 book by the philosopher Derek Parfit, in which the author discusses ethics, rationality and personal identity. It is divided into four parts, dedicated to self-defeating theories, rationality and time, personal ...
'', he describes a thought experiment known as the teletransportation paradox. In Buddhist philosophy, the concept of
anattā In Buddhism, the term ''anattā'' () or ''anātman'' () is the doctrine of "no-self" – that no unchanging, permanent self or essence can be found in any phenomenon. While often interpreted as a doctrine denying the existence of a self, ''ana ...
refers to the idea that the self is an illusion. Other philosophers have argued that Hellie's vertiginous question has a number of philosophical implications relating to the
metaphysical Metaphysics is the branch of philosophy that examines the basic structure of reality. It is traditionally seen as the study of mind-independent features of the world, but some theorists view it as an inquiry into the conceptual framework of h ...
nature of consciousness.
Christian List Christian List (born 1973) is a German philosopher and political scientist who serves as professor of philosophy and decision theory at the Ludwig Maximilian University of Munich and co-director of the Munich Center for Mathematical Philosop ...
argues that the vertiginous question and the existence of first-personal facts is evidence against physicalism, and evidence against other third-personal metaphysical pictures, including standard versions of
dualism Dualism most commonly refers to: * Mind–body dualism, a philosophical view which holds that mental phenomena are, at least in certain respects, not physical phenomena, or that the mind and the body are distinct and separable from one another * P ...
. List also argues that the vertiginous question implies a "quadrilemma" for theories of consciousness. He claims that at most three of the following metaphysical claims can be true: 'first-person realism', 'non-
solipsism Solipsism ( ; ) is the philosophical idea that only one's mind is sure to exist. As an epistemological position, solipsism holds that knowledge of anything outside one's own mind is unsure; the external world and other minds cannot be known ...
', 'non-fragmentation', and 'one world' – and at at least one of these four must be false. List has proposed a model he calls the "many-worlds theory of consciousness" in order to reconcile the subjective nature of consciousness without lapsing into solipsism. Vincent Conitzer argues that the nature of identity is connected to
A series and B series In metaphysics, the A series and the B series are two different descriptions of the temporal ordering relation among events. The two series differ principally in their use of tense to describe the temporal relation between events and the resulti ...
theories of time, and that A-theory being true implies that the "I" is metaphysically distinguished from other perspectives. Other philosophical theories regarding the metaphysical nature of self are Caspar Hare's theories of
perspectival realism In Caspar Hare's theory of perspectival realism, there is a defining ''intrinsic'' property that the things that are in perceptual awareness have. Consider seeing object A but not object B. Of course, we can say that the visual experience of A i ...
, in which things within perceptual awareness have a defining intrinsic property that exists absolutely and not relative to anything, and
egocentric presentism Egocentric presentism is a form of solipsism introduced by Caspar Hare in which other persons can be conscious, but their experiences are simply not . Similarly, in related work, Hare argues for a theory of perspectival realism in which other pe ...
, in which the experiences of other individuals are not ''present'' in the way that one's current perspective is.


Scientific study

For many decades, consciousness as a research topic was avoided by the majority of mainstream scientists, because of a general feeling that a phenomenon defined in subjective terms could not properly be studied using objective experimental methods. In 1975 George Mandler published an influential psychological study which distinguished between slow, serial, and limited conscious processes and fast, parallel and extensive unconscious ones. The Science and Religion Forum 1984 annual conference, From Artificial Intelligence to Human Consciousness''' identified the nature of consciousness as a matter for investigation;
Donald Michie Donald Michie (; 11 November 1923 – 7 July 2007) was a British researcher in artificial intelligence. During World War II, Michie worked for the Government Code and Cypher School at Bletchley Park, contributing to the effort to solve " Tunny ...
was a keynote speaker. Starting in the 1980s, an expanding community of neuroscientists and psychologists have associated themselves with a field called ''Consciousness Studies'', giving rise to a stream of experimental work published in books, journals such as '' Consciousness and Cognition'', ''Frontiers in Consciousness Research'', '' Psyche'', and the '' Journal of Consciousness Studies'', along with regular conferences organized by groups such as the Association for the Scientific Study of Consciousness and the Society for Consciousness Studies. Modern medical and psychological investigations into consciousness are based on psychological experiments (including, for example, the investigation of priming effects using
subliminal stimuli Subliminal stimuli (; ' literally "below" or "less than") are any sensory stimulus (physiology), stimuli below an individual's sensory threshold, threshold or limit for conscious perception, in contrast to stimuli (above threshold). Visual stimul ...
), and on
case studies A case study is an in-depth, detailed examination of a particular case (or cases) within a real-world context. For example, case studies in medicine may focus on an individual patient or ailment; case studies in business might cover a particular fi ...
of alterations in consciousness produced by trauma, illness, or drugs. Broadly viewed, scientific approaches are based on two core concepts. The first identifies the content of consciousness with the experiences that are reported by human subjects; the second makes use of the concept of consciousness that has been developed by neurologists and other medical professionals who deal with patients whose behavior is impaired. In either case, the ultimate goals are to develop techniques for assessing consciousness objectively in humans as well as other animals, and to understand the neural and psychological mechanisms that underlie it.


Measurement via verbal report

Experimental research on consciousness presents special difficulties, due to the lack of a universally accepted
operational definition An operational definition specifies concrete, replicable procedures designed to represent a construct. In the words of American psychologist S.S. Stevens (1935), "An operation is the performance which we execute in order to make known a concept." F ...
. In the majority of experiments that are specifically about consciousness, the subjects are human, and the criterion used is verbal report: in other words, subjects are asked to describe their experiences, and their descriptions are treated as observations of the contents of consciousness. For example, subjects who stare continuously at a
Necker cube The Necker cube is an optical illusion that was first published as a rhomboid in 1832 by Swiss crystallographer Louis Albert Necker. It is a simple wire-frame, two dimensional drawing of a cube with no visual cues as to its orientation, so i ...
usually report that they experience it "flipping" between two 3D configurations, even though the stimulus itself remains the same. The objective is to understand the relationship between the conscious awareness of stimuli (as indicated by verbal report) and the effects the stimuli have on brain activity and behavior. In several paradigms, such as the technique of response priming, the behavior of subjects is clearly influenced by stimuli for which they report no awareness, and suitable experimental manipulations can lead to increasing priming effects despite decreasing prime identification (double dissociation). Verbal report is widely considered to be the most reliable indicator of consciousness, but it raises a number of issues. For one thing, if verbal reports are treated as observations, akin to observations in other branches of science, then the possibility arises that they may contain errors—but it is difficult to make sense of the idea that subjects could be wrong about their own experiences, and even more difficult to see how such an error could be detected. Daniel Dennett has argued for an approach he calls heterophenomenology, which means treating verbal reports as stories that may or may not be true, but his ideas about how to do this have not been widely adopted. Another issue with verbal report as a criterion is that it restricts the field of study to humans who have language: this approach cannot be used to study consciousness in other species, pre-linguistic children, or people with types of brain damage that impair language. As a third issue, philosophers who dispute the validity of the
Turing test The Turing test, originally called the imitation game by Alan Turing in 1949,. Turing wrote about the ‘imitation game’ centrally and extensively throughout his 1950 text, but apparently retired the term thereafter. He referred to ‘ iste ...
may feel that it is possible, at least in principle, for verbal report to be dissociated from consciousness entirely: a philosophical zombie may give detailed verbal reports of awareness in the absence of any genuine awareness. Although verbal report is in practice the "gold standard" for ascribing consciousness, it is not the only possible criterion. In medicine, consciousness is assessed as a combination of verbal behavior, arousal, brain activity, and purposeful movement. The last three of these can be used as indicators of consciousness when verbal behavior is absent. The
scientific literature Scientific literature encompasses a vast body of academic papers that spans various disciplines within the natural and social sciences. It primarily consists of academic papers that present original empirical research and theoretical ...
regarding the neural bases of arousal and purposeful movement is very extensive. Their reliability as indicators of consciousness is disputed, however, due to numerous studies showing that alert human subjects can be induced to behave purposefully in a variety of ways in spite of reporting a complete lack of awareness. Studies related to the
neuroscience of free will The neuroscience of free will, a part of neurophilosophy, is the study of topics related to free will (including Volition (psychology), volition and the sense of agency), using neuroscience and the analysis of how findings from such studies may ...
have also shown that the influence consciousness has on decision-making is not always straightforward.


Mirror test and contingency awareness

Another approach applies specifically to the study of
self-awareness In philosophy of self, philosophy, self-awareness is the awareness and reflection of one's own personality or individuality, including traits, feelings, and behaviors. It is not to be confused with consciousness in the sense of qualia. While ...
, that is, the ability to distinguish oneself from others. In the 1970s Gordon Gallup developed an operational test for self-awareness, known as the
mirror test The mirror test—sometimes called the mark test, mirror self-recognition (MSR) test, red spot technique, or rouge test—is a behavioral technique developed in 1970 by American psychologist Gordon Gallup Jr. to determine whether an animal posse ...
. The test examines whether animals are able to differentiate between seeing themselves in a mirror versus seeing other animals. The classic example involves placing a spot of coloring on the skin or fur near the individual's forehead and seeing if they attempt to remove it or at least touch the spot, thus indicating that they recognize that the individual they are seeing in the mirror is themselves. Humans (older than 18 months) and other
great apes The Hominidae (), whose members are known as the great apes or hominids (), are a taxonomic family of primates that includes eight extant species in four genera: '' Pongo'' (the Bornean, Sumatran and Tapanuli orangutan); '' Gorilla'' (the ...
,
bottlenose dolphin The bottlenose dolphin is a toothed whale in the genus ''Tursiops''. They are common, cosmopolitan members of the family Delphinidae, the family of oceanic dolphins. Molecular studies show the genus contains three species: the common bot ...
s,
orca The orca (''Orcinus orca''), or killer whale, is a toothed whale and the largest member of the oceanic dolphin family. The only extant species in the genus '' Orcinus'', it is recognizable by its black-and-white-patterned body. A cosmopol ...
s, pigeons, European magpies and
elephants Elephants are the Largest and heaviest animals, largest living land animals. Three living species are currently recognised: the African bush elephant (''Loxodonta africana''), the African forest elephant (''L. cyclotis''), and the Asian ele ...
have all been observed to pass this test. While some other animals like
pig The pig (''Sus domesticus''), also called swine (: swine) or hog, is an omnivorous, domesticated, even-toed, hoofed mammal. It is named the domestic pig when distinguishing it from other members of the genus '' Sus''. Some authorities cons ...
s have been shown to find food by looking into the mirror. Contingency awareness is another such approach, which is basically the conscious understanding of one's actions and its effects on one's environment. It is recognized as a factor in self-recognition. The brain processes during contingency awareness and learning is believed to rely on an intact
medial temporal lobe The temporal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain. The temporal lobe is involved in pr ...
and age. A study done in 2020 involving transcranial direct current stimulation,
Magnetic resonance imaging Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to generate pictures of the anatomy and the physiological processes inside the body. MRI scanners use strong magnetic fields, magnetic field gradients, and ...
(MRI) and eyeblink classical conditioning supported the idea that the
parietal cortex The parietal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The parietal lobe is positioned above the temporal lobe and behind the frontal lobe and central sulcus. The parietal lobe integrates sensory informa ...
serves as a substrate for contingency awareness and that age-related disruption of this region is sufficient to impair awareness.


Neural correlates

A major part of the scientific literature on consciousness consists of studies that examine the relationship between the experiences reported by subjects and the activity that simultaneously takes place in their brains—that is, studies of the
neural correlates of consciousness The neural correlates of consciousness (NCC) are the minimal set of neuronal events and mechanisms sufficient for the occurrence of the mental states to which they are related. Neuroscientists use empirical approaches to discover neural correla ...
. The hope is to find that activity in a particular part of the brain, or a particular pattern of global brain activity, which will be strongly predictive of conscious awareness. Several brain imaging techniques, such as EEG and
fMRI Functional magnetic resonance imaging or functional MRI (fMRI) measures brain activity by detecting changes associated with blood flow. This technique relies on the fact that cerebral blood flow and neuronal activation are coupled. When an area o ...
, have been used for physical measures of brain activity in these studies. Another idea that has drawn attention for several decades is that consciousness is associated with high-frequency (gamma band) oscillations in brain activity. This idea arose from proposals in the 1980s, by Christof von der Malsburg and Wolf Singer, that gamma oscillations could solve the so-called
binding problem The unity of consciousness and (cognitive) binding problem is the problem of how objects, background, and abstract or emotional features are combined into a single experience. The binding problem refers to the overall encoding of our brain circuit ...
, by linking information represented in different parts of the brain into a unified experience. Rodolfo Llinás, for example, proposed that consciousness results from recurrent thalamo-cortical resonance where the specific thalamocortical systems (content) and the non-specific (centromedial thalamus) thalamocortical systems (context) interact in the
gamma Gamma (; uppercase , lowercase ; ) is the third letter of the Greek alphabet. In the system of Greek numerals it has a value of 3. In Ancient Greek, the letter gamma represented a voiced velar stop . In Modern Greek, this letter normally repr ...
band frequency via synchronous oscillations. A number of studies have shown that activity in primary sensory areas of the brain is not sufficient to produce consciousness: it is possible for subjects to report a lack of awareness even when areas such as the primary visual cortex (V1) show clear electrical responses to a stimulus. Higher brain areas are seen as more promising, especially the
prefrontal cortex In mammalian brain anatomy, the prefrontal cortex (PFC) covers the front part of the frontal lobe of the cerebral cortex. It is the association cortex in the frontal lobe. The PFC contains the Brodmann areas BA8, BA9, BA10, BA11, BA12, ...
, which is involved in a range of higher cognitive functions collectively known as
executive functions In cognitive science and neuropsychology, executive functions (collectively referred to as executive function and cognitive control) are a set of cognitive processes that support goal-directed behavior, by regulating thoughts and actions thro ...
. There is substantial evidence that a "top-down" flow of neural activity (i.e., activity propagating from the frontal cortex to sensory areas) is more predictive of conscious awareness than a "bottom-up" flow of activity. The prefrontal cortex is not the only candidate area, however: studies by Nikos Logothetis and his colleagues have shown, for example, that visually responsive neurons in parts of the
temporal lobe The temporal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain. The temporal lobe is involved in pr ...
reflect the visual perception in the situation when conflicting visual images are presented to different eyes (i.e., bistable percepts during binocular rivalry). Furthermore, top-down feedback from higher to lower visual brain areas may be weaker or absent in the peripheral visual field, as suggested by some experimental data and theoretical arguments; nevertheless humans can perceive visual inputs in the peripheral visual field arising from bottom-up V1 neural activities. Meanwhile, bottom-up V1 activities for the central visual fields can be vetoed, and thus made invisible to perception, by the top-down feedback, when these bottom-up signals are inconsistent with the brain's internal model of the visual world. Modulation of neural responses may correlate with phenomenal experiences. In contrast to the raw electrical responses that do not correlate with consciousness, the modulation of these responses by other stimuli correlates surprisingly well with an important aspect of consciousness: namely with the phenomenal experience of stimulus intensity (brightness, contrast). In the research group of Danko Nikolić it has been shown that some of the changes in the subjectively perceived brightness correlated with the modulation of firing rates while others correlated with the modulation of neural synchrony. An fMRI investigation suggested that these findings were strictly limited to the primary visual areas. This indicates that, in the primary visual areas, changes in firing rates and synchrony can be considered as neural correlates of qualia—at least for some type of qualia. In 2013, the perturbational complexity index (PCI) was proposed, a measure of the algorithmic complexity of the electrophysiological response of the cortex to
transcranial magnetic stimulation Transcranial magnetic stimulation (TMS) is a noninvasive neurostimulation technique in which a changing magnetic field is used to induce an electric current in a targeted area of the brain through electromagnetic induction. A device called a st ...
. This measure was shown to be higher in individuals that are awake, in REM sleep or in a locked-in state than in those who are in deep sleep or in a vegetative state, making it potentially useful as a quantitative assessment of consciousness states. Assuming that not only humans but even some non-mammalian species are conscious, a number of evolutionary approaches to the problem of neural correlates of consciousness open up. For example, assuming that birds are conscious—a common assumption among neuroscientists and ethologists due to the extensive cognitive repertoire of birds—there are comparative neuroanatomical ways to validate some of the principal, currently competing, mammalian consciousness–brain theories. The rationale for such a comparative study is that the avian brain deviates structurally from the mammalian brain. So how similar are they? What homologs can be identified? The general conclusion from the study by Butler, et al. is that some of the major theories for the mammalian brain also appear to be valid for the avian brain. The structures assumed to be critical for consciousness in mammalian brains have homologous counterparts in avian brains. Thus the main portions of the theories of Crick and Koch, Edelman and Tononi, and Cotterill seem to be compatible with the assumption that birds are conscious. Edelman also differentiates between what he calls primary consciousness (which is a trait shared by humans and non-human animals) and higher-order consciousness as it appears in humans alone along with human language capacity. Certain aspects of the three theories, however, seem less easy to apply to the hypothesis of avian consciousness. For instance, the suggestion by Crick and Koch that layer 5 neurons of the mammalian brain have a special role, seems difficult to apply to the avian brain, since the avian homologs have a different morphology. Likewise, the theory of Eccles seems incompatible, since a structural homolog/analogue to the dendron has not been found in avian brains. The assumption of an avian consciousness also brings the reptilian brain into focus. The reason is the structural continuity between avian and reptilian brains, meaning that the phylogenetic origin of consciousness may be earlier than suggested by many leading neuroscientists. Joaquin Fuster of UCLA has advocated the position of the importance of the prefrontal cortex in humans, along with the areas of Wernicke and Broca, as being of particular importance to the development of human language capacities neuro-anatomically necessary for the emergence of higher-order consciousness in humans. A study in 2016 looked at lesions in specific areas of the brainstem that were associated with
coma A coma is a deep state of prolonged unconsciousness in which a person cannot be awakened, fails to Nociception, respond normally to Pain, painful stimuli, light, or sound, lacks a normal Circadian rhythm, sleep-wake cycle and does not initiate ...
and vegetative states. A small region of the rostral dorsolateral
pontine tegmentum The pontine tegmentum, or dorsal pons, is the dorsal part of the pons located within the brainstem. The ventral part or ventral pons is known as the basilar part of the pons, or basilar pons. Along with the dorsal surface of the medulla oblonga ...
in the brainstem was suggested to drive consciousness through functional connectivity with two cortical regions, the left ventral anterior insular cortex, and the pregenual
anterior cingulate cortex In human brains, the anterior cingulate cortex (ACC) is the frontal part of the cingulate cortex that resembles a "collar" surrounding the frontal part of the corpus callosum. It consists of Brodmann areas 24, 32, and 33. It is involved ...
. These three regions may work together as a triad to maintain consciousness.
Krista and Tatiana Hogan Krista and Tatiana Hogan (born October 25, 2006) are two Canadian conjoined craniopagus twins. They are joined at the head and have separate brains that are interconnected by a thalamic bridge within a shared skull. They were born in Vancouver, ...
have a unique thalamic connection may provide insight into the philosophical and neurological foundations of consciousness. It has been argued that there's no empirical test that can conclusively establish that for some sensations, the twins share one token experience rather than two exactly matching token experiences. Yet background considerations about the way the brain has specific locations for conscious contents, combined with the evident overlapping pathways in the twins' brains, arguably implies that the twins share some conscious experiences. If this is true, then the twins may offer a proof of concept for how experiences in general could be shared between brains.


Models

A wide range of empirical theories of consciousness have been proposed. Adrian Doerig and colleagues list 13 notable theories, while Anil Seth and Tim Bayne list 22 notable theories.


Global workspace theory

Global workspace theory Global workspace theory (GWT) is a framework for thinking about consciousness introduced in 1988, by cognitive scientist Bernard Baars. It was developed to qualitatively explain a large set of matched pairs of conscious and unconscious processes. ...
(GWT) is a
cognitive architecture A cognitive architecture is both a theory about the structure of the human mind and to a computational instantiation of such a theory used in the fields of artificial intelligence (AI) and computational cognitive science. These formalized models ...
and theory of consciousness proposed by the cognitive psychologist
Bernard Baars Bernard J. Baars (born 1946 in Amsterdam, the Netherlands) is a former Senior Fellow in Theoretical Neurobiology at the Neurosciences Institute in San Diego, US. He is currently an Affiliated Fellow there. He is best known as the originator of ...
in 1988. Baars explains the theory with the metaphor of a theater, with conscious processes represented by an illuminated stage. This theater integrates inputs from a variety of unconscious and otherwise autonomous networks in the brain and then broadcasts them to unconscious networks (represented in the metaphor by a broad, unlit "audience"). The theory has since been expanded upon by other scientists including cognitive neuroscientist Stanislas Dehaene and Lionel Naccache.


Integrated information theory

Integrated information theory (IIT), pioneered by neuroscientist Giulio Tononi in 2004, postulates that consciousness resides in the information being processed and arises once the information reaches a certain level of complexity. Additionally, IIT is one of the only leading theories of consciousness that attempts to create a 1:1 mapping between conscious states and precise, formal mathematical descriptions of those mental states. Proponents of this model suggest that it may provide a physical grounding for consciousness in neurons, as they provide the mechanism by which information is integrated. This also relates to the "
hard problem of consciousness In the philosophy of mind, the hard problem of consciousness is to explain why and how humans and other organisms have qualia, phenomenal consciousness, or subjective experience. It is contrasted with the "easy problems" of explaining why and how ...
" proposed by
David Chalmers David John Chalmers (; born 20 April 1966) is an Australian philosopher and cognitive scientist, specializing in philosophy of mind and philosophy of language. He is a professor of philosophy and neural science at New York University, as well ...
. The theory remains controversial, because of its lack of credibility.


Orchestrated objective reduction

Orchestrated objective reduction (Orch-OR), or the quantum theory of mind, was proposed by scientists
Roger Penrose Sir Roger Penrose (born 8 August 1931) is an English mathematician, mathematical physicist, Philosophy of science, philosopher of science and Nobel Prize in Physics, Nobel Laureate in Physics. He is Emeritus Rouse Ball Professor of Mathematics i ...
and Stuart Hameroff, and states that consciousness originates at the quantum level inside neurons. The mechanism is held to be a quantum process called objective reduction that is orchestrated by cellular structures called
microtubule Microtubules are polymers of tubulin that form part of the cytoskeleton and provide structure and shape to eukaryotic cells. Microtubules can be as long as 50 micrometres, as wide as 23 to 27 nanometer, nm and have an inner diameter bet ...
s, which form the cytoskeleton around which the brain is built. The duo proposed that these quantum processes accounted for creativity, innovation, and problem-solving abilities. Penrose published his views in the book ''
The Emperor's New Mind ''The Emperor's New Mind: Concerning Computers, Minds and The Laws of Physics'' is a 1989 book by the mathematical physicist Roger Penrose. Penrose argues that human consciousness is non-algorithmic, and thus is not capable of being modeled by ...
''. In 2014, the discovery of quantum vibrations inside microtubules gave new life to the argument.


Attention schema theory

In 2011,
Michael Graziano Michael Steven Anthony Graziano (born May 22, 1967) is an American scientist A scientist is a person who Scientific method, researches to advance knowledge in an Branches of science, area of the natural sciences. In classical antiquity, there ...
and Kastner proposed the "attention schema" theory of awareness. In that theory, specific cortical areas, notably in the superior temporal sulcus and the temporo-parietal junction, are used to build the construct of awareness and attribute it to other people. The same cortical machinery is also used to attribute awareness to oneself. Damage to these cortical regions can lead to deficits in consciousness such as
hemispatial neglect Hemispatial neglect is a neuropsychological condition in which, after damage to one hemisphere of the brain (e.g. after a stroke), a deficit in attention and awareness towards the side of space opposite brain damage (contralesional space) is obs ...
. In the
attention Attention or focus, is the concentration of awareness on some phenomenon to the exclusion of other stimuli. It is the selective concentration on discrete information, either subjectively or objectively. William James (1890) wrote that "Atte ...
schema theory, the value of explaining the feature of awareness and attributing it to a person is to gain a useful predictive model of that person's attentional processing.
Attention Attention or focus, is the concentration of awareness on some phenomenon to the exclusion of other stimuli. It is the selective concentration on discrete information, either subjectively or objectively. William James (1890) wrote that "Atte ...
is a style of
information processing In cognitive psychology, information processing is an approach to the goal of understanding human thinking that treats cognition as essentially Computing, computational in nature, with the mind being the ''software'' and the brain being the ''hard ...
in which a brain focuses its resources on a limited set of interrelated signals. Awareness, in this theory, is a useful, simplified schema that represents attentional states. To be aware of X is explained by constructing a model of one's attentional focus on X.


Entropic brain theory

The entropic brain is a theory of conscious states informed by neuroimaging research with
psychedelic drugs Psychedelics are a subclass of Hallucinogen, hallucinogenic drugs whose primary effect is to trigger psychoactive drug, non-ordinary mental states (known as psychedelic experiences or "trips") and a perceived "expansion of consciousness". Also ...
. The theory suggests that the brain in primary states such as rapid eye movement (REM) sleep, early
psychosis In psychopathology, psychosis is a condition in which a person is unable to distinguish, in their experience of life, between what is and is not real. Examples of psychotic symptoms are delusions, hallucinations, and disorganized or inco ...
and under the influence of psychedelic drugs, is in a disordered state; normal waking consciousness constrains some of this freedom and makes possible metacognitive functions such as internal self-administered
reality testing Reality testing is the psychotherapeutic function by which the objective or real world and one's relationship to it are reflected on and evaluated by the observer. This process of distinguishing the internal world of thoughts and feelings from the ...
and
self-awareness In philosophy of self, philosophy, self-awareness is the awareness and reflection of one's own personality or individuality, including traits, feelings, and behaviors. It is not to be confused with consciousness in the sense of qualia. While ...
. Criticism has included questioning whether the theory has been adequately tested.


Projective consciousness model

In 2017, work by David Rudrauf and colleagues, including Karl Friston, applied the active inference paradigm to consciousness, leading to the projective consciousness model (PCM), a model of how sensory data is integrated with priors in a process of projective transformation. The authors argue that, while their model identifies a key relationship between computation and phenomenology, it does not completely solve the hard problem of consciousness or completely close the
explanatory gap In the philosophy of mind, the explanatory gap is the difficulty that physicalist philosophies have in explaining how physical properties give rise to the way things feel subjectively when they are experienced. It is a term introduced by philoso ...
.


Claustrum being the conductor for consciousness

In 2004, a proposal was made by molecular biologist
Francis Crick Francis Harry Compton Crick (8 June 1916 – 28 July 2004) was an English molecular biologist, biophysicist, and neuroscientist. He, James Watson, Rosalind Franklin, and Maurice Wilkins played crucial roles in deciphering the Nucleic acid doub ...
(co-discoverer of the double helix), which stated that to bind together an individual's experience, a conductor of an orchestra is required. Together with neuroscientist
Christof Koch Christof Koch ( ; born November 13, 1956) is an American cognitive scientist, neurophysiologist and computational neuroscientist best known for his work on the neural basis of consciousness. He was the president and chief scientist of the All ...
, he proposed that this conductor would have to collate information rapidly from various regions of the brain. The duo reckoned that the
claustrum The claustrum (Latin, meaning "to close" or "to shut") is a thin sheet of neurons and supporting glial cells in the brain, that connects to the cerebral cortex and subcortical regions including the amygdala, hippocampus and thalamus. It is locate ...
was well suited for the task. However, Crick died while working on the idea. The proposal is backed by a study done in 2014, where a team at the
George Washington University The George Washington University (GW or GWU) is a Private university, private University charter#Federal, federally-chartered research university in Washington, D.C., United States. Originally named Columbian College, it was chartered in 1821 by ...
induced unconsciousness in a 54-year-old woman suffering from intractable epilepsy by stimulating her claustrum. The woman underwent depth electrode implantation and electrical stimulation mapping. The electrode between the left claustrum and anterior-dorsal insula was the one which induced unconsciousness. Correlation for interactions affecting medial parietal and posterior frontal channels during stimulation increased significantly as well. Their findings suggested that the left claustrum or anterior insula is an important part of a network that subserves consciousness, and that disruption of consciousness is related to increased EEG signal synchrony within frontal-parietal networks. However, this remains an isolated, hence inconclusive study.


Biological function and evolution

The emergence of consciousness during
biological evolution Evolution is the change in the heritable characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, resulting in certai ...
remains a topic of ongoing scientific inquiry. The survival value of consciousness is still a matter of exploration and understanding. While consciousness appears to play a crucial role in human cognition, decision-making, and self-awareness, its adaptive significance across different species remains a subject of debate. Some people question whether consciousness has any survival value. Some argue that consciousness is a by-product of evolution.
Thomas Henry Huxley Thomas Henry Huxley (4 May 1825 – 29 June 1895) was an English biologist and anthropologist who specialized in comparative anatomy. He has become known as "Darwin's Bulldog" for his advocacy of Charles Darwin's theory of evolution. The stor ...
for example defends in an essay titled "On the Hypothesis that Animals are
Automata An automaton (; : automata or automatons) is a relatively self-operating machine, or control mechanism designed to automatically follow a sequence of operations, or respond to predetermined instructions. Some automata, such as bellstrikers i ...
, and its History" an epiphenomenalist theory of consciousness, according to which consciousness is a causally inert effect of neural activity—"as the steam-whistle which accompanies the work of a locomotive engine is without influence upon its machinery". To this
William James William James (January 11, 1842 – August 26, 1910) was an American philosopher and psychologist. The first educator to offer a psychology course in the United States, he is considered to be one of the leading thinkers of the late 19th c ...
objects in his essay ''Are We Automata?'' by stating an evolutionary argument for mind-brain interaction implying that if the preservation and development of consciousness in the biological evolution is a result of
natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the Heredity, heritable traits characteristic of a population over generation ...
, it is plausible that consciousness has not only been influenced by neural processes, but has had a survival value itself; and it could only have had this if it had been efficacious.
Karl Popper Sir Karl Raimund Popper (28 July 1902 – 17 September 1994) was an Austrian–British philosopher, academic and social commentator. One of the 20th century's most influential philosophers of science, Popper is known for his rejection of the ...
develops a similar evolutionary argument in the book ''The Self and Its Brain''. Opinions are divided on when and how consciousness first arose. It has been argued that consciousness emerged (i) exclusively with the first humans, (ii) exclusively with the first mammals, (iii) independently in mammals and birds, or (iv) with the first reptiles. Other authors date the origins of consciousness to the first animals with nervous systems or early vertebrates in the Cambrian over 500 million years ago.
Donald Griffin Donald Redfield Griffin (August 3, 1915 – November 7, 2003) was an American professor of zoology at various universities who conducted seminal research in animal behavior, animal navigation, acoustic orientation and sensory biophysics. In 1938 ...
suggests in his book ''Animal Minds'' a gradual evolution of consciousness. Further exploration of the origins of consciousness, particularly in molluscs, has been done by Peter Godfrey Smith in his book ''Metazoa''. Regarding the primary function of conscious processing, a recurring idea in recent theories is that phenomenal states somehow integrate neural activities and information-processing that would otherwise be independent. This has been called the ''integration consensus''. Another example has been proposed by Gerald Edelman called dynamic core hypothesis which puts emphasis on reentrant connections that reciprocally link areas of the brain in a massively parallel manner. Edelman also stresses the importance of the evolutionary emergence of higher-order consciousness in humans from the historically older trait of primary consciousness which humans share with non-human animals (see '' Neural correlates'' section above). These theories of integrative function present solutions to two classic problems associated with consciousness: differentiation and unity. They show how our conscious experience can discriminate between a virtually unlimited number of different possible scenes and details (differentiation) because it integrates those details from our sensory systems, while the integrative nature of consciousness in this view easily explains how our experience can seem unified as one whole despite all of these individual parts. However, it remains unspecified which kinds of information are integrated in a conscious manner and which kinds can be integrated without consciousness. Nor is it explained what specific causal role conscious integration plays, nor why the same functionality cannot be achieved without consciousness. Not all kinds of information are capable of being disseminated consciously (e.g., neural activity related to vegetative functions, reflexes, unconscious motor programs, low-level perceptual analyzes, etc.), and many kinds of information can be disseminated and combined with other kinds without consciousness, as in intersensory interactions such as the ventriloquism effect. Hence it remains unclear why any of it is conscious. For a review of the differences between conscious and unconscious integrations, see the article of Ezequiel Morsella. As noted earlier, even among writers who consider consciousness to be well-defined, there is widespread dispute about which animals other than humans can be said to possess it. Edelman has described this distinction as that of humans possessing higher-order consciousness while sharing the trait of primary consciousness with non-human animals (see previous paragraph). Thus, any examination of the evolution of consciousness is faced with great difficulties. Nevertheless, some writers have argued that consciousness can be viewed from the standpoint of
evolutionary biology Evolutionary biology is the subfield of biology that studies the evolutionary processes such as natural selection, common descent, and speciation that produced the diversity of life on Earth. In the 1930s, the discipline of evolutionary biolo ...
as an
adaptation In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the p ...
in the sense of a trait that increases fitness. In his article "Evolution of consciousness", John Eccles argued that special anatomical and physical properties of the mammalian
cerebral cortex The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. It is the largest site of Neuron, neural integration in the central nervous system, and plays ...
gave rise to consciousness (" psychon ... linked to dendron through quantum physics"). Bernard Baars proposed that once in place, this "recursive" circuitry may have provided a basis for the subsequent development of many of the functions that consciousness facilitates in higher organisms. Peter Carruthers has put forth one such potential adaptive advantage gained by conscious creatures by suggesting that consciousness allows an individual to make distinctions between appearance and reality. This ability would enable a creature to recognize the likelihood that their perceptions are deceiving them (e.g. that water in the distance may be a mirage) and behave accordingly, and it could also facilitate the manipulation of others by recognizing how things appear to them for both cooperative and devious ends. Other philosophers, however, have suggested that consciousness would not be necessary for any functional advantage in evolutionary processes. No one has given a causal explanation, they argue, of why it would not be possible for a functionally equivalent non-conscious organism (i.e., a philosophical zombie) to achieve the very same survival advantages as a conscious organism. If evolutionary processes are blind to the difference between function ''F'' being performed by conscious organism ''O'' and non-conscious organism ''O*'', it is unclear what adaptive advantage consciousness could provide. As a result, an exaptive explanation of consciousness has gained favor with some theorists that posit consciousness did not evolve as an adaptation but was an
exaptation Exaptation or co-option is a shift in the function of a trait during evolution. For example, a trait can evolve because it served one particular function, but subsequently it may come to serve another. Exaptations are common in both anatomy and be ...
arising as a consequence of other developments such as increases in brain size or cortical rearrangement. Consciousness in this sense has been compared to the blind spot in the retina where it is not an adaption of the retina, but instead just a by-product of the way the retinal axons were wired. Several scholars including
Pinker Pinker may refer to: People * George Pinker (1924–2007), British obstetrician and gynecologist * Rachel Pinker, American meteorologist * Robert Pinker (1931–2021), British sociologist *Steven Pinker Steven Arthur Pinker (born September 1 ...
,
Chomsky Avram Noam Chomsky (born December 7, 1928) is an American professor and public intellectual known for his work in linguistics, political activism, and social criticism. Sometimes called "the father of modern linguistics", Chomsky is also a ...
, Edelman, and Luria have indicated the importance of the emergence of human language as an important regulative mechanism of learning and memory in the context of the development of higher-order consciousness (see '' Neural correlates'' section above).


Altered states

There are some brain states in which consciousness seems to be absent, including dreamless sleep or coma. There are also a variety of circumstances that can change the relationship between the mind and the world in less drastic ways, producing what are known as altered states of consciousness. Some altered states occur naturally; others can be produced by drugs or brain damage. Altered states can be accompanied by changes in thinking, disturbances in the sense of time, feelings of loss of control, changes in emotional expression, alternations in body image and changes in meaning or significance. The two most widely accepted altered states are
sleep Sleep is a state of reduced mental and physical activity in which consciousness is altered and certain Sensory nervous system, sensory activity is inhibited. During sleep, there is a marked decrease in muscle activity and interactions with th ...
and
dream A dream is a succession of images, ideas, emotions, and sensation (psychology), sensations that usually occur involuntarily in the mind during certain stages of sleep. Humans spend about two hours dreaming per night, and each dream lasts around ...
ing. Although dream sleep and non-dream sleep appear very similar to an outside observer, each is associated with a distinct pattern of brain activity, metabolic activity, and eye movement; each is also associated with a distinct pattern of experience and cognition. During ordinary non-dream sleep, people who are awakened report only vague and sketchy thoughts, and their experiences do not cohere into a continuous narrative. During dream sleep, in contrast, people who are awakened report rich and detailed experiences in which events form a continuous progression, which may however be interrupted by bizarre or fantastic intrusions. Thought processes during the dream state frequently show a high level of irrationality. Both dream and non-dream states are associated with severe disruption of memory: it usually disappears in seconds during the non-dream state, and in minutes after awakening from a dream unless actively refreshed. Research conducted on the effects of partial epileptic seizures on consciousness found that patients who have partial epileptic seizures experience altered states of consciousness. In partial epileptic seizures, consciousness is impaired or lost while some aspects of consciousness, often automated behaviors, remain intact. Studies found that when measuring the qualitative features during partial epileptic seizures, patients exhibited an increase in arousal and became absorbed in the experience of the seizure, followed by difficulty in focusing and shifting attention. A variety of
psychoactive drug A psychoactive drug, psychopharmaceutical, mind-altering drug, consciousness-altering drug, psychoactive substance, or psychotropic substance is a chemical substance that alters psychological functioning by modulating central nervous system acti ...
s, including
alcohol Alcohol may refer to: Common uses * Alcohol (chemistry), a class of compounds * Ethanol, one of several alcohols, commonly known as alcohol in everyday life ** Alcohol (drug), intoxicant found in alcoholic beverages ** Alcoholic beverage, an alco ...
, have notable effects on consciousness. These range from a simple dulling of awareness produced by
sedative A sedative or tranquilliser is a substance that induces sedation by reducing irritability or Psychomotor agitation, excitement. They are central nervous system (CNS) Depressant, depressants and interact with brain activity, causing its decelera ...
s, to increases in the intensity of sensory qualities produced by
stimulant Stimulants (also known as central nervous system stimulants, or psychostimulants, or colloquially as uppers) are a class of drugs that increase alertness. They are used for various purposes, such as enhancing attention, motivation, cognition, ...
s,
cannabis ''Cannabis'' () is a genus of flowering plants in the family Cannabaceae that is widely accepted as being indigenous to and originating from the continent of Asia. However, the number of species is disputed, with as many as three species be ...
, empathogens–entactogens such as
MDMA 3,4-Methylenedioxymethamphetamine (MDMA), commonly known as ecstasy (tablet form), and molly (crystal form), is an empathogen–entactogenic drug with stimulant and minor Psychedelic drug, psychedelic properties. In studies, it has been used ...
("Ecstasy"), or most notably by the class of drugs known as
psychedelics Psychedelics are a subclass of hallucinogenic drugs whose primary effect is to trigger non-ordinary mental states (known as psychedelic experiences or "trips") and a perceived "expansion of consciousness". Also referred to as classic halluci ...
.
LSD Lysergic acid diethylamide, commonly known as LSD (from German ; often referred to as acid or lucy), is a semisynthetic, hallucinogenic compound derived from ergot, known for its powerful psychological effects and serotonergic activity. I ...
,
mescaline Mescaline, also known as mescalin or mezcalin, and in chemical terms 3,4,5-trimethoxyphenethylamine, is a natural product, naturally occurring psychedelic drug, psychedelic alkaloid, protoalkaloid of the substituted phenethylamine class, found ...
,
psilocybin Psilocybin, also known as 4-phosphoryloxy-''N'',''N''-dimethyltryptamine (4-PO-DMT), is a natural product, naturally occurring tryptamine alkaloid and Investigational New Drug, investigational drug found in more than List of psilocybin mushroom ...
,
dimethyltryptamine Dimethyltryptamine (DMT), also known as ''N'',''N''-dimethyltryptamine (''N'',''N''-DMT), is a Psychedelic drug, serotonergic hallucinogen and Investigational New Drug, investigational drug of the substituted tryptamine, tryptamine family tha ...
, and others in this group can produce major distortions of perception, including hallucinations; some users even describe their drug-induced experiences as mystical or spiritual in quality. The brain mechanisms underlying these effects are not as well understood as those induced by use of alcohol, but there is substantial evidence that alterations in the brain system that uses the chemical neurotransmitter
serotonin Serotonin (), also known as 5-hydroxytryptamine (5-HT), is a monoamine neurotransmitter with a wide range of functions in both the central nervous system (CNS) and also peripheral tissues. It is involved in mood, cognition, reward, learning, ...
play an essential role. There has been some research into physiological changes in yogis and people who practise various techniques of
meditation Meditation is a practice in which an individual uses a technique to train attention and awareness and detach from reflexive, "discursive thinking", achieving a mentally clear and emotionally calm and stable state, while not judging the meditat ...
. Some research with brain waves during meditation has reported differences between those corresponding to ordinary relaxation and those corresponding to meditation. It has been disputed, however, whether there is enough evidence to count these as physiologically distinct states of consciousness. The most extensive study of the characteristics of altered states of consciousness was made by psychologist Charles Tart in the 1960s and 1970s. Tart analyzed a state of consciousness as made up of a number of component processes, including exteroception (sensing the external world);
interoception Interoception is the collection of Sense#Other internal sensations and perceptions, senses providing information to the organism about the internal state of the body. This can be both conscious and subconscious. It encompasses the brain's process ...
(sensing the body); input-processing (seeing meaning); emotions; memory; time sense; sense of identity; evaluation and cognitive processing; motor output; and interaction with the environment. Each of these, in his view, could be altered in multiple ways by drugs or other manipulations. The components that Tart identified have not, however, been validated by empirical studies. Research in this area has not yet reached firm conclusions, but a recent questionnaire-based study identified eleven significant factors contributing to drug-induced states of consciousness: experience of unity; spiritual experience; blissful state; insightfulness; disembodiment; impaired control and cognition; anxiety; complex imagery; elementary imagery; audio-visual
synesthesia Synesthesia (American English) or synaesthesia (British English) is a perceptual phenomenon in which stimulation of one sensory or cognitive pathway leads to involuntary experiences in a second sensory or cognitive pathway. People with sy ...
; and changed meaning of percepts.


Medical aspects

The medical approach to consciousness is scientifically oriented. It derives from a need to treat people whose brain function has been impaired as a result of disease, brain damage, toxins, or drugs. In medicine, conceptual distinctions are considered useful to the degree that they can help to guide treatments. The medical approach focuses mostly on the amount of consciousness a person has: in medicine, consciousness is assessed as a "level" ranging from coma and brain death at the low end, to full alertness and purposeful responsiveness at the high end. Consciousness is of concern to patients and physicians, especially
neurologists Neurology (from , "string, nerve" and the suffix -logia, "study of") is the branch of medicine dealing with the diagnosis and treatment of all categories of conditions and disease involving the nervous system, which comprises the brain, the s ...
and anesthesiologists. Patients may have disorders of consciousness or may need to be anesthetized for a surgical procedure. Physicians may perform consciousness-related interventions such as instructing the patient to sleep, administering
general anesthesia General anaesthesia (UK) or general anesthesia (US) is medically induced loss of consciousness that renders a patient unarousable even by painful stimuli. It is achieved through medications, which can be injected or inhaled, often with an analgesi ...
, or inducing medical coma. Also,
bioethicists Bioethics is both a field of study and professional practice, interested in ethical issues related to health (primarily focused on the human, but also increasingly includes animal ethics), including those emerging from advances in biology, medi ...
may be concerned with the ethical implications of consciousness in medical cases of patients such as the
Karen Ann Quinlan case ''In re Quinlan'' (70 N.J. 10, 355 A.2d 647 (NJ 1976)) was a landmark 1975 court case in the United States in which the parents of a woman who was kept alive by artificial means were allowed to order her removal from artificial ventilation. Kar ...
, while neuroscientists may study patients with impaired consciousness in hopes of gaining information about how the brain works.


Assessment

In medicine, consciousness is examined using a set of procedures known as
neuropsychological assessment Over the past three millennia, scholars have attempted to establish connections between localized brain damage and corresponding behavioral changes. A significant advancement in this area occurred between 1942 and 1948, when Soviet neuropsycholog ...
. There are two commonly used methods for assessing the level of consciousness of a patient: a simple procedure that requires minimal training, and a more complex procedure that requires substantial expertise. The simple procedure begins by asking whether the patient is able to move and react to physical stimuli. If so, the next question is whether the patient can respond in a meaningful way to questions and commands. If so, the patient is asked for name, current location, and current day and time. A patient who can answer all of these questions is said to be "alert and oriented times four" (sometimes denoted "A&Ox4" on a medical chart), and is usually considered fully conscious. The more complex procedure is known as a
neurological examination A neurological examination is the assessment of sensory neuron and motor responses, especially reflexes, to determine whether the nervous system is impaired. This typically includes a physical examination and a review of the patient's medical his ...
, and is usually carried out by a
neurologist Neurology (from , "string, nerve" and the suffix -logia, "study of") is the branch of medicine dealing with the diagnosis and treatment of all categories of conditions and disease involving the nervous system, which comprises the brain, the ...
in a hospital setting. A formal neurological examination runs through a precisely delineated series of tests, beginning with tests for basic sensorimotor reflexes, and culminating with tests for sophisticated use of language. The outcome may be summarized using the Glasgow Coma Scale, which yields a number in the range 3–15, with a score of 3 to 8 indicating coma, and 15 indicating full consciousness. The Glasgow Coma Scale has three subscales, measuring the best motor response (ranging from "no motor response" to "obeys commands"), the best eye response (ranging from "no eye opening" to "eyes opening spontaneously") and the best verbal response (ranging from "no verbal response" to "fully oriented"). There is also a simpler
pediatric Pediatrics (American English) also spelled paediatrics (British English), is the branch of medicine that involves the medical care of infants, children, adolescents, and young adults. In the United Kingdom, pediatrics covers many of their youth ...
version of the scale, for children too young to be able to use language. In 2013, an experimental procedure was developed to measure degrees of consciousness, the procedure involving stimulating the brain with a magnetic pulse, measuring resulting waves of electrical activity, and developing a consciousness score based on the complexity of the brain activity.


Disorders

Medical conditions that inhibit consciousness are considered
disorders of consciousness Disorders of consciousness are medical conditions that inhibit consciousness. Some define disorders of consciousness as any change from complete self-awareness to inhibited or absent self-awareness and arousal. This category generally includes m ...
. This category generally includes minimally conscious state and
persistent vegetative state A vegetative state (VS) or post-coma unresponsiveness (PCU) is a disorder of consciousness in which patients with severe brain damage are in a state of partial arousal rather than true awareness. After four weeks in a vegetative state, the patie ...
, but sometimes also includes the less severe
locked-in syndrome Locked-in syndrome (LIS), also known as pseudocoma, is a condition in which a patient is aware but cannot move or communicate verbally due to complete paralysis of nearly all voluntary muscles in their body except for vertical eye movements and ...
and more severe chronic coma.
Differential diagnosis In healthcare, a differential diagnosis (DDx) is a method of analysis that distinguishes a particular disease or condition from others that present with similar clinical features. Differential diagnostic procedures are used by clinicians to di ...
of these disorders is an active area of
biomedical research Medical research (or biomedical research), also known as health research, refers to the process of using scientific methods with the aim to produce knowledge about human diseases, the prevention and treatment of illness, and the promotion of ...
. Finally,
brain death Brain death is the permanent, irreversible, and complete loss of Electroencephalography, brain function, which may include cessation of involuntary activity (e.g., Control of ventilation#Control of respiratory rhythm, breathing) necessary to su ...
results in possible irreversible disruption of consciousness. While other conditions may cause a moderate deterioration (e.g.,
dementia Dementia is a syndrome associated with many neurodegenerative diseases, characterized by a general decline in cognitive abilities that affects a person's ability to perform activities of daily living, everyday activities. This typically invo ...
and
delirium Delirium (formerly acute confusional state, an ambiguous term that is now discouraged) is a specific state of acute confusion attributable to the direct physiological consequence of a medical condition, effects of a psychoactive substance, or ...
) or transient interruption (e.g., grand mal and petit mal seizures) of consciousness, they are not included in this category. Medical experts increasingly view anosognosia as a disorder of consciousness. ''Anosognosia'' is a Greek-derived term meaning "unawareness of disease". This is a condition in which patients are disabled in some way, most commonly as a result of a
stroke Stroke is a medical condition in which poor cerebral circulation, blood flow to a part of the brain causes cell death. There are two main types of stroke: brain ischemia, ischemic, due to lack of blood flow, and intracranial hemorrhage, hemor ...
, but either misunderstand the nature of the problem or deny that there is anything wrong with them. The most frequently occurring form is seen in people who have experienced a stroke damaging the
parietal lobe The parietal lobe is one of the four Lobes of the brain, major lobes of the cerebral cortex in the brain of mammals. The parietal lobe is positioned above the temporal lobe and behind the frontal lobe and central sulcus. The parietal lobe integra ...
in the right hemisphere of the brain, giving rise to a syndrome known as
hemispatial neglect Hemispatial neglect is a neuropsychological condition in which, after damage to one hemisphere of the brain (e.g. after a stroke), a deficit in attention and awareness towards the side of space opposite brain damage (contralesional space) is obs ...
, characterized by an inability to direct action or attention toward objects located to the left with respect to their bodies. Patients with hemispatial neglect are often paralyzed on the left side of the body, but sometimes deny being unable to move. When questioned about the obvious problem, the patient may avoid giving a direct answer, or may give an explanation that does not make sense. Patients with hemispatial neglect may also fail to recognize paralyzed parts of their bodies: one frequently mentioned case is of a man who repeatedly tried to throw his own paralyzed right leg out of the bed he was lying in, and when asked what he was doing, complained that somebody had put a dead leg into the bed with him. An even more striking type of anosognosia is Anton–Babinski syndrome, a rarely occurring condition in which patients become blind but claim to be able to see normally, and persist in this claim in spite of all evidence to the contrary.


Outside human adults


In children

Of the eight types of consciousness in the Lycan classification, some are detectable in utero and others develop years after birth. Psychologist and educator William Foulkes studied children's dreams and concluded that prior to the shift in cognitive maturation that humans experience during ages five to seven, children lack the Lockean consciousness that Lycan had labeled "introspective consciousness" and that Foulkes labels "self-reflection". In a 2020 paper, Katherine Nelson and Robyn Fivush use "autobiographical consciousness" to label essentially the same faculty, and agree with Foulkes on the timing of this faculty's acquisition. Nelson and Fivush contend that "language is the tool by which humans create a new, uniquely human form of consciousness, namely, autobiographical consciousness".
Julian Jaynes Julian Jaynes (February 27, 1920 – November 21, 1997) was an American psychologist who worked at the universities of Yale and Princeton for nearly 25 years and became best known for his 1976 book '' The Origin of Consciousness in the Break ...
had staked out these positions decades earlier. Citing the developmental steps that lead the infant to autobiographical consciousness, Nelson and Fivush point to the acquisition of "
theory of mind In psychology and philosophy, theory of mind (often abbreviated to ToM) refers to the capacity to understand other individuals by ascribing mental states to them. A theory of mind includes the understanding that others' beliefs, desires, intent ...
", calling theory of mind "necessary for autobiographical consciousness" and defining it as "understanding differences between one's own mind and others' minds in terms of beliefs, desires, emotions and thoughts". They write, "The hallmark of theory of mind, the understanding of false belief, occurs ... at five to six years of age".


In animals

The topic of animal consciousness is beset by a number of difficulties. It poses the problem of other minds in an especially severe form, because non-human animals, lacking the ability to express human language, cannot tell humans about their experiences. Also, it is difficult to reason objectively about the question, because a denial that an animal is conscious is often taken to imply that it does not feel, its life has no value, and that harming it is not morally wrong. Descartes, for example, has sometimes been blamed for mistreatment of animals due to the fact that he believed only humans have a non-physical mind. Most people have a strong intuition that some animals, such as cats and dogs, are conscious, while others, such as insects, are not; but the sources of this intuition are not obvious, and are often based on personal interactions with pets and other animals they have observed. Philosophers who consider subjective experience the essence of consciousness also generally believe, as a correlate, that the existence and nature of animal consciousness can never rigorously be known. Thomas Nagel spelled out this point of view in an influential essay titled " What Is it Like to Be a Bat?". He said that an organism is conscious "if and only if there is something that it is like to be that organism—something it is like ''for'' the organism"; and he argued that no matter how much we know about an animal's brain and behavior, we can never really put ourselves into the mind of the animal and experience its world in the way it does itself. Other thinkers, such as
Douglas Hofstadter Douglas Richard Hofstadter (born 15 February 1945) is an American cognitive and computer scientist whose research includes concepts such as the sense of self in relation to the external world, consciousness, analogy-making, Strange loop, strange ...
, dismiss this argument as incoherent. Several psychologists and ethologists have argued for the existence of animal consciousness by describing a range of behaviors that appear to show animals holding beliefs about things they cannot directly perceive—
Donald Griffin Donald Redfield Griffin (August 3, 1915 – November 7, 2003) was an American professor of zoology at various universities who conducted seminal research in animal behavior, animal navigation, acoustic orientation and sensory biophysics. In 1938 ...
's 2001 book ''Animal Minds'' reviews a substantial portion of the evidence. On July 7, 2012, eminent scientists from different branches of neuroscience gathered at the
University of Cambridge The University of Cambridge is a Public university, public collegiate university, collegiate research university in Cambridge, England. Founded in 1209, the University of Cambridge is the List of oldest universities in continuous operation, wo ...
to celebrate the Francis Crick Memorial Conference, which deals with consciousness in humans and pre-linguistic consciousness in nonhuman animals. After the conference, they signed in the presence of
Stephen Hawking Stephen William Hawking (8January 194214March 2018) was an English theoretical physics, theoretical physicist, cosmologist, and author who was director of research at the Centre for Theoretical Cosmology at the University of Cambridge. Between ...
, the 'Cambridge Declaration on Consciousness', which summarizes the most important findings of the survey: "We decided to reach a consensus and make a statement directed to the public that is not scientific. It's obvious to everyone in this room that animals have consciousness, but it is not obvious to the rest of the world. It is not obvious to the rest of the Western world or the Far East. It is not obvious to the society." "Convergent evidence indicates that non-human animals ..., including all mammals and birds, and other creatures, ... have the necessary neural substrates of consciousness and the capacity to exhibit intentional behaviors."


In artificial intelligence

The idea of an artifact made conscious is an ancient theme of mythology, appearing for example in the Greek myth of Pygmalion, who carved a statue that was magically brought to life, and in medieval Jewish stories of the
Golem A golem ( ; ) is an animated Anthropomorphism, anthropomorphic being in Jewish folklore, which is created entirely from inanimate matter, usually clay or mud. The most famous golem narrative involves Judah Loew ben Bezalel, the late 16th-century ...
, a magically animated
homunculus A homunculus ( , , ; "little person", : homunculi , , ) is a small human being. Popularized in 16th-century alchemy and 19th-century fiction, it has historically referred to the creation of a miniature, fully formed human. The concept has root ...
built of clay. However, the possibility of actually constructing a conscious machine was probably first discussed by
Ada Lovelace Augusta Ada King, Countess of Lovelace (''née'' Byron; 10 December 1815 – 27 November 1852), also known as Ada Lovelace, was an English mathematician and writer chiefly known for her work on Charles Babbage's proposed mechanical general-pur ...
, in a set of notes written in 1842 about the Analytical Engine invented by
Charles Babbage Charles Babbage (; 26 December 1791 – 18 October 1871) was an English polymath. A mathematician, philosopher, inventor and mechanical engineer, Babbage originated the concept of a digital programmable computer. Babbage is considered ...
, a precursor (never built) to modern electronic computers. Lovelace was essentially dismissive of the idea that a machine such as the Analytical Engine could think in a humanlike way. She wrote: One of the most influential contributions to this question was an essay written in 1950 by pioneering computer scientist
Alan Turing Alan Mathison Turing (; 23 June 1912 – 7 June 1954) was an English mathematician, computer scientist, logician, cryptanalyst, philosopher and theoretical biologist. He was highly influential in the development of theoretical computer ...
, titled ''
Computing Machinery and Intelligence "Computing Machinery and Intelligence" is a seminal paper written by Alan Turing on the topic of artificial intelligence. The paper, published in 1950 in ''Mind (journal), Mind'', was the first to introduce his concept of what is now known as th ...
''. Turing disavowed any interest in terminology, saying that even "Can machines think?" is too loaded with spurious connotations to be meaningful; but he proposed to replace all such questions with a specific operational test, which has become known as the
Turing test The Turing test, originally called the imitation game by Alan Turing in 1949,. Turing wrote about the ‘imitation game’ centrally and extensively throughout his 1950 text, but apparently retired the term thereafter. He referred to ‘ iste ...
. To pass the test, a computer must be able to imitate a human well enough to fool interrogators. In his essay Turing discussed a variety of possible objections, and presented a counterargument to each of them. The Turing test is commonly cited in discussions of
artificial intelligence Artificial intelligence (AI) is the capability of computer, computational systems to perform tasks typically associated with human intelligence, such as learning, reasoning, problem-solving, perception, and decision-making. It is a field of re ...
as a proposed criterion for machine consciousness; it has provoked a great deal of philosophical debate. For example, Daniel Dennett and
Douglas Hofstadter Douglas Richard Hofstadter (born 15 February 1945) is an American cognitive and computer scientist whose research includes concepts such as the sense of self in relation to the external world, consciousness, analogy-making, Strange loop, strange ...
argue that anything capable of passing the Turing test is necessarily conscious, while
David Chalmers David John Chalmers (; born 20 April 1966) is an Australian philosopher and cognitive scientist, specializing in philosophy of mind and philosophy of language. He is a professor of philosophy and neural science at New York University, as well ...
argues that a
philosophical zombie A philosophical zombie (or "p-zombie") is a being in a thought experiment in the philosophy of mind that is physically identical to a normal human being but does not have conscious experience. For example, if a philosophical zombie were poked ...
could pass the test, yet fail to be conscious. A third group of scholars have argued that with technological growth once machines begin to display any substantial signs of human-like behavior then the dichotomy (of human consciousness compared to human-like consciousness) becomes passé and issues of machine autonomy begin to prevail even as observed in its nascent form within contemporary industry and
technology Technology is the application of Conceptual model, conceptual knowledge to achieve practical goals, especially in a reproducible way. The word ''technology'' can also mean the products resulting from such efforts, including both tangible too ...
. Jürgen Schmidhuber argues that consciousness is the result of compression. As an agent sees representation of itself recurring in the environment, the compression of this representation can be called consciousness. In a lively exchange over what has come to be referred to as "the
Chinese room The Chinese room argument holds that a computer executing a program cannot have a mind, understanding, or consciousness, regardless of how intelligently or human-like the program may make the computer behave. The argument was presented in a 19 ...
argument",
John Searle John Rogers Searle (; born July 31, 1932) is an American philosopher widely noted for contributions to the philosophy of language, philosophy of mind, and social philosophy. He began teaching at UC Berkeley in 1959 and was Willis S. and Mario ...
sought to refute the claim of proponents of what he calls "strong artificial intelligence (AI)" that a computer program can be conscious, though he does agree with advocates of "weak AI" that computer programs can be formatted to "simulate" conscious states. His own view is that consciousness has subjective, first-person causal powers by being essentially intentional due to the way human brains function biologically; conscious persons can perform computations, but consciousness is not inherently computational the way computer programs are. To make a Turing machine that speaks Chinese, Searle imagines a room with one monolingual English speaker (Searle himself, in fact), a book that designates a combination of Chinese symbols to be output paired with Chinese symbol input, and boxes filled with Chinese symbols. In this case, the English speaker is acting as a computer and the rulebook as a program. Searle argues that with such a machine, he would be able to process the inputs to outputs perfectly without having any understanding of Chinese, nor having any idea what the questions and answers could possibly mean. If the experiment were done in English, since Searle knows English, he would be able to take questions and give answers without any algorithms for English questions, and he would be effectively aware of what was being said and the purposes it might serve. Searle would pass the Turing test of answering the questions in both languages, but he is only conscious of what he is doing when he speaks English. Another way of putting the argument is to say that computer programs can pass the Turing test for processing the syntax of a language, but that the syntax cannot lead to semantic meaning in the way strong AI advocates hoped. In the literature concerning artificial intelligence, Searle's essay has been second only to Turing's in the volume of debate it has generated. Searle himself was vague about what extra ingredients it would take to make a machine conscious: all he proposed was that what was needed was "causal powers" of the sort that the brain has and that computers lack. But other thinkers sympathetic to his basic argument have suggested that the necessary (though perhaps still not sufficient) extra conditions may include the ability to pass not just the verbal version of the Turing test, but the
robotic Robotics is the interdisciplinary study and practice of the design, construction, operation, and use of robots. Within mechanical engineering, robotics is the design and construction of the physical structures of robots, while in computer s ...
version, which requires grounding the robot's words in the robot's sensorimotor capacity to categorize and interact with the things in the world that its words are about, Turing-indistinguishably from a real person. Turing-scale robotics is an empirical branch of research on
embodied cognition Embodied cognition represents a diverse group of theories which investigate how cognition is shaped by the bodily state and capacities of the organism. These embodied factors include the motor system, the perceptual system, bodily interactions wi ...
and
situated cognition Situated cognition is a theory that posits that knowing is inseparable from doing by arguing that all knowledge is situated in activity bound to social, cultural and physical contexts. Situativity theorists suggest a model of knowledge and learnin ...
. In 2014, Victor Argonov has suggested a non-Turing test for machine consciousness based on a machine's ability to produce philosophical judgments. He argues that a deterministic machine must be regarded as conscious if it is able to produce judgments on all problematic properties of consciousness (such as qualia or binding) having no innate (preloaded) philosophical knowledge on these issues, no philosophical discussions while learning, and no informational models of other creatures in its memory (such models may implicitly or explicitly contain knowledge about these creatures' consciousness). However, this test can be used only to detect, but not refute the existence of consciousness. A positive result proves that a machine is conscious but a negative result proves nothing. For example, absence of philosophical judgments may be caused by lack of the machine's intellect, not by absence of consciousness.


Stream of consciousness

William James William James (January 11, 1842 – August 26, 1910) was an American philosopher and psychologist. The first educator to offer a psychology course in the United States, he is considered to be one of the leading thinkers of the late 19th c ...
is usually credited with popularizing the idea that human consciousness flows like a stream, in his ''Principles of Psychology'' of 1890. According to James, the "stream of thought" is governed by five characteristics: # ''Every thought tends to be part of a personal consciousness.'' # ''Within each personal consciousness thought is always changing.'' # ''Within each personal consciousness thought is sensibly continuous.'' # ''It always appears to deal with objects independent of itself.'' # ''It is interested in some parts of these objects to the exclusion of others.'' A similar concept appears in Buddhist philosophy, expressed by the Sanskrit term ''Citta-saṃtāna'', which is usually translated as
mindstream Mindstream (Pali: ''citta-santāna'', Sanskrit: ''citta-saṃtāna;'' Ch: ''xin xiangxu'' 心相續) in Buddhist philosophy is the moment-to-moment continuum of sense impressions and mental phenomena ( citta), which is also described as continui ...
or "mental continuum". Buddhist teachings describe that consciousness manifests moment to moment as sense impressions and mental phenomena that are continuously changing. The teachings list six triggers that can result in the generation of different mental events. These triggers are input from the five senses (seeing, hearing, smelling, tasting or touch sensations), or a thought (relating to the past, present or the future) that happen to arise in the mind. The mental events generated as a result of these triggers are: feelings, perceptions and intentions/behaviour. The moment-by-moment manifestation of the mind-stream is said to happen in every person all the time. It even happens in a scientist who analyzes various phenomena in the world, or analyzes the material body including the organ brain. The manifestation of the mindstream is also described as being influenced by physical laws, biological laws, psychological laws, volitional laws, and universal laws. The purpose of the Buddhist practice of
mindfulness Mindfulness is the cognitive skill, usually developed through exercises, of sustaining metacognitive awareness towards the contents of one's own mind and bodily sensations in the present moment. The term ''mindfulness'' derives from the Pali ...
is to understand the inherent nature of the consciousness and its characteristics.


Narrative form

In the West, the primary impact of the idea has been on literature rather than science: " stream of consciousness as a narrative mode" means writing in a way that attempts to portray the moment-to-moment thoughts and experiences of a character. This technique perhaps had its beginnings in the monologues of Shakespeare's plays and reached its fullest development in the novels of
James Joyce James Augustine Aloysius Joyce (born James Augusta Joyce; 2 February 1882 – 13 January 1941) was an Irish novelist, poet, and literary critic. He contributed to the modernist avant-garde movement and is regarded as one of the most influentia ...
and
Virginia Woolf Adeline Virginia Woolf (; ; 25 January 1882 28 March 1941) was an English writer and one of the most influential 20th-century modernist authors. She helped to pioneer the use of stream of consciousness narration as a literary device. Vir ...
, although it has also been used by many other noted writers. Here, for example, is a passage from Joyce's '' Ulysses'' about the thoughts of Molly Bloom:


Spiritual approaches

The
Upanishads The Upanishads (; , , ) are late Vedic and post-Vedic Sanskrit texts that "document the transition from the archaic ritualism of the Veda into new religious ideas and institutions" and the emergence of the central religious concepts of Hind ...
hold the oldest recorded map of consciousness, as explored by sages through meditation. The Canadian psychiatrist
Richard Maurice Bucke Richard Maurice Bucke (18 March 1837 – 19 February 1902) was a Canadian psychiatrist in the late 19th century. An adventurer during his youth, Bucke later studied medicine. Eventually, as a psychiatrist, he headed the provincial Asylum for the ...
, author of the 1901 book '' Cosmic Consciousness: A Study in the Evolution of the Human Mind'', distinguished between three types of consciousness: 'Simple Consciousness', awareness of the body, possessed by many animals; 'Self Consciousness', awareness of being aware, possessed only by humans; and 'Cosmic Consciousness', awareness of the life and order of the universe, possessed only by humans who have attained "intellectual enlightenment or illumination". Another thorough account of the spiritual approach is
Ken Wilber Kenneth Earl Wilber II (born January 31, 1949) is an American theorist and writer on transpersonal psychology and his own integral theory, a four-quadrant grid which purports to encompass all human knowledge and experience. Starting publishing ...
's 1977 book ''The Spectrum of Consciousness'', a comparison of western and eastern ways of thinking about the mind. Wilber described consciousness as a spectrum with ordinary awareness at one end, and more profound types of awareness at higher levels. Other examples include the various levels of spiritual consciousness presented by Prem Saran Satsangi and Stuart Hameroff.


See also

* * * * * * * * *


Notes


References


Further reading

* * * * * * * * * * *


Articles

* Lewis, Ralph.
An Overview of the Leading Theories of Consciousness
Organizing and comparing the major candidate theories in the field.'' Psychology Today, November 25, 2023.


External links

* * * * * {{Authority control Cognitive neuroscience Cognitive psychology Concepts in epistemology Concepts in the philosophy of mind Concepts in the philosophy of science Emergence Mental processes Metaphysical properties Metaphysics of mind Neuropsychological assessment Ontology Phenomenology Theory of mind