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Benjamin Libet (; April 12, 1916 – July 23, 2007) was an American
neuroscientist A neuroscientist (or neurobiologist) is a scientist who has specialised knowledge in neuroscience, a branch of biology that deals with the physiology, biochemistry, psychology, anatomy and molecular biology of neurons, neural circuits, and glial ...
who was a pioneer in the field of human
consciousness Consciousness, at its simplest, is sentience and awareness of internal and external existence. However, the lack of definitions has led to millennia of analyses, explanations and debates by philosophers, theologians, linguisticians, and scien ...
. Libet was a researcher in the
physiology Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemic ...
department of the
University of California, San Francisco The University of California, San Francisco (UCSF) is a public land-grant research university in San Francisco, California. It is part of the University of California system and is dedicated entirely to health science and life science. It ...
. In 2003, he was the first recipient of the ''Virtual Nobel Prize in Psychology'' from the University of Klagenfurt, "for his pioneering achievements in the experimental investigation of consciousness, initiation of action, and free will".


Life

He was the son of Ukrainian Jewish immigrants. Gamer Libitsky, his paternal grandfather, came to America in 1865 from a town called Brusilov in
Ukraine Ukraine ( uk, Україна, Ukraïna, ) is a country in Eastern Europe. It is the second-largest European country after Russia, which it borders to the east and northeast. Ukraine covers approximately . Prior to the ongoing Russian inva ...
. His mother, Anna Charovsky, emigrated from
Kiev Kyiv, also spelled Kiev, is the capital and most populous city of Ukraine. It is in north-central Ukraine along the Dnieper River. As of 1 January 2021, its population was 2,962,180, making Kyiv the seventh-most populous city in Europe. Ky ...
in 1913. His parents first met in
Chicago (''City in a Garden''); I Will , image_map = , map_caption = Interactive Map of Chicago , coordinates = , coordinates_footnotes = , subdivision_type = List of sovereign states, Count ...
. They were married in 1915, and somewhat over nine months later Benjamin was born. He had a brother Meyer, and a sister Dorothy. Libet attended a public
elementary school A primary school (in Ireland, the United Kingdom, Australia, Trinidad and Tobago, Jamaica, and South Africa), junior school (in Australia), elementary school or grade school (in North America and the Philippines) is a school for primary ed ...
and John Marshall High School. In 1939, Libet graduated from the
University of Chicago The University of Chicago (UChicago, Chicago, U of C, or UChi) is a private research university in Chicago, Illinois. Its main campus is located in Chicago's Hyde Park neighborhood. The University of Chicago is consistently ranked among the b ...
, where he studied with
Ralph W. Gerard Ralph Waldo Gerard (7 October 1900 – 17 February 1974) was an American neurophysiologist and behavioral scientist known for his wide-ranging work on the nervous system, nerve metabolism, psychopharmacology, and biological basis of schizophrenia. ...
. In the 1970s, Libet was involved in research into
neural In biology, the nervous system is the highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes ...
activity and sensation thresholds. His initial investigations involved determining how much activation at specific sites in the brain was required to trigger artificial somatic sensations, relying on routine psychophysical procedures. This work soon crossed into an investigation into human consciousness; his most famous experiment was meant to demonstrate that the unconscious electrical processes in the brain called
Bereitschaftspotential In neurology, the Bereitschaftspotential or BP (German for "readiness potential"), also called the pre-motor potential or readiness potential (RP), is a measure of activity in the motor cortex and supplementary motor area of the brain leading up t ...
(or readiness potential) discovered by
Lüder Deecke Lüder Deecke (; born 22 June 1938) in Lohe-Rickelshof, Germany is a German Austrian neurologist, neuroscientist, teacher and physician whose scientific discoveries have influenced brain research and the treatment and rehabilitation of neurolog ...
and
Hans Helmut Kornhuber Hans Helmut Kornhuber (24 February 1928 – 30 October 2009) was a German neurologist and neurophysiologist. Biography Hans Helmut Kornhuber was born as the second of three children of Dr. med. Gertrud and Dr. Arnold Kornhuber. He grew up a ...
in 1965 precede conscious decisions to perform volitional, spontaneous acts, implying that unconscious neuronal processes precede and potentially cause volitional acts which are retrospectively felt to be consciously motivated by the subject. The experiment has caused controversy not only because it challenges the belief in free will, but also due to a criticism of its implicit assumptions.


Volitional acts and readiness potential


Equipment

To gauge the relation between unconscious readiness potential and subjective feelings of volition and action, Libet required an
objective Objective may refer to: * Objective (optics), an element in a camera or microscope * ''The Objective'', a 2008 science fiction horror film * Objective pronoun, a personal pronoun that is used as a grammatical object * Objective Productions, a Brit ...
method of marking the subject's conscious experience of the will to perform an action in time, and afterward comparing this information with data recording the brain's electrical activity during the same interval. For this, Libet required specialized pieces of equipment. The first of these was the
cathode ray Cathode rays or electron beam (e-beam) are streams of electrons observed in discharge tubes. If an evacuated glass tube is equipped with two electrodes and a voltage is applied, glass behind the positive electrode is observed to glow, due to el ...
oscilloscope An oscilloscope (informally a scope) is a type of electronic test instrument that graphically displays varying electrical voltages as a two-dimensional plot of one or more signals as a function of time. The main purposes are to display repetiti ...
, an instrument typically used to graph the
amplitude The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of am ...
and
frequency Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...
of electrical signals. With a few adjustments, however, the oscilloscope could be made to act as a timer: instead of displaying a series of waves, the output was a single dot that could be made to travel in a circular motion, similar to the movements of a second hand around a clock face. This timer was set so that the time it took for the dot to travel between intervals marked on the oscilloscope was approximately forty-three
milliseconds A millisecond (from ''milli-'' and second; symbol: ms) is a unit of time in the International System of Units (SI) equal to one thousandth (0.001 or 10−3 or 1/1000) of a second and to 1000 microseconds. A unit of 10 milliseconds may be called ...
. As the
angular velocity In physics, angular velocity or rotational velocity ( or ), also known as angular frequency vector,(UP1) is a pseudovector representation of how fast the angular position or orientation of an object changes with time (i.e. how quickly an object ...
of the dot remained constant, any change in distance could easily be converted into the time it took to travel that distance. To monitor brain activity during the same period, Libet used an
electroencephalogram Electroencephalography (EEG) is a method to record an electrogram of the spontaneous electrical activity of the brain. The biosignals detected by EEG have been shown to represent the postsynaptic potentials of pyramidal neurons in the neocortex ...
(EEG). The EEG uses small
electrodes An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials dep ...
placed at various points on the scalp that measure neuronal activity in the
cortex Cortex or cortical may refer to: Biology * Cortex (anatomy), the outermost layer of an organ ** Cerebral cortex, the outer layer of the vertebrate cerebrum, part of which is the ''forebrain'' *** Motor cortex, the regions of the cerebral cortex i ...
, the outermost portion of the
brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as Visual perception, vision. I ...
, which is associated with higher
cognition Cognition refers to "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, though ...
. The transmission of electrical signals across regions of the cortex causes differences in measured voltage across EEG electrodes. These differences in voltage reflect changes in neuronal activity in specific areas of the cortex. To measure the actual time of the voluntary motor act, an
electromyograph Electromyography (EMG) is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph to produce a record called an electromyogram. An electromyo ...
(EMG) recorded the muscle movement using electrodes on the skin over the activated muscle of the forearm. The EMG time was taken as the zero time relative to which all other times were calculated.


Methods

Researchers carrying out Libet's procedure would ask each participant to sit at a desk in front of the oscilloscope timer. They would affix the EEG electrodes to the participant's scalp, and would then instruct the subject to carry out some small, simple motor activity, such as pressing a button, or flexing a finger or wrist, within a certain time frame. No limits were placed on the number of times the subject could perform the action within this period. During the experiment, the subject would be asked to note the position of the dot on the oscilloscope timer when "he/she was first aware of the wish or urge to act" (control tests with Libet's equipment demonstrated a comfortable
margin of error The margin of error is a statistic expressing the amount of random sampling error in the results of a survey. The larger the margin of error, the less confidence one should have that a poll result would reflect the result of a census of the e ...
of only −50 milliseconds). Pressing the button also recorded the position of the dot on the oscillator, this time electronically. By comparing the marked time of the button's pushing and the subject's conscious decision to act, researchers were able to calculate the total time of the trial from the subject's initial volition through to the resultant action. On average, approximately two hundred milliseconds elapsed between the first appearance of conscious will to press the button and the act of pressing it. Researchers also analyzed EEG recordings for each trial with respect to the timing of the action. It was noted that brain activity involved in the initiation of the action, primarily centered in the secondary
motor cortex The motor cortex is the region of the cerebral cortex believed to be involved in the planning, control, and execution of voluntary movements. The motor cortex is an area of the frontal lobe located in the posterior precentral gyrus immediately ...
, occurred, on average, approximately five hundred milliseconds ''before'' the trial ended with the pushing of the button. That is to say, researchers recorded mounting brain activity related to the resultant action as many as three hundred milliseconds ''before'' subjects reported the first awareness of conscious will to act. In other words, apparently conscious decisions to act were ''preceded'' by an unconscious buildup of electrical activity within the brain – the change in EEG signals reflecting this buildup came to be called
Bereitschaftspotential In neurology, the Bereitschaftspotential or BP (German for "readiness potential"), also called the pre-motor potential or readiness potential (RP), is a measure of activity in the motor cortex and supplementary motor area of the brain leading up t ...
or
readiness potential In neurology, the Bereitschaftspotential or BP ( German for "readiness potential"), also called the pre-motor potential or readiness potential (RP), is a measure of activity in the motor cortex and supplementary motor area of the brain leading up t ...
. As of 2008, the upcoming outcome of a decision could be found in study of the brain activity in the prefrontal and parietal cortex up to 7 seconds before the subject was aware of their decision. Since then, even the readiness potential argument has been refuted.


Implications of Libet's experiments

There is no majority agreement about the interpretation or the significance of Libet's experiments. However, Libet's experiments suggest to some that unconscious processes in the brain are the true initiator of volitional acts, and
free will Free will is the capacity of agents to choose between different possible courses of action unimpeded. Free will is closely linked to the concepts of moral responsibility, praise, culpability, sin, and other judgements which apply only to ac ...
therefore plays no part in their initiation. If unconscious brain processes have already taken steps to initiate an action before consciousness is aware of any desire to perform it, the causal role of consciousness in volition is all but eliminated, according to this interpretation. For instance,
Susan Blackmore Susan Jane Blackmore (born 29 July 1951) is a British writer, lecturer, sceptic, broadcaster, and a Visiting Professor at the University of Plymouth. Her fields of research include memetics, parapsychology, consciousness, and she is best known ...
's interpretation is "that conscious experience takes some time to build up and is much too slow to be responsible for making things happen." Such a conclusion would be overdrawn as in a subsequent run of experiments, Libet found that even after the awareness of the decision to push the button had happened, people still had the capability to veto the decision and not to push the button. So they still had the capability to refrain from the decision that had earlier been made. Some therefore take this brain impulse to push the button to suggest just a readiness potential which the subject may either then go along with or may veto. So the person still has power over his or her decision. For this reason, Libet himself regards his experimental results to be entirely compatible with the notion of free will. He finds that conscious volition is exercised in the form of 'the power of veto' (sometimes called "free won't"); the idea that conscious acquiescence is required to allow the unconscious buildup of the
readiness potential In neurology, the Bereitschaftspotential or BP ( German for "readiness potential"), also called the pre-motor potential or readiness potential (RP), is a measure of activity in the motor cortex and supplementary motor area of the brain leading up t ...
to be actualized as a movement. While consciousness plays no part in the ''instigation'' of volitional acts, Libet suggested that it may still have a part to play in suppressing or withholding certain acts instigated by the unconscious. Libet noted that everyone has experienced the withholding from performing an unconscious urge. Since the subjective experience of the conscious will to act preceded the action by only 200 milliseconds, this leaves consciousness only 100–150 milliseconds to veto an action (this is because the final 20 milliseconds prior to an act are occupied by the activation of the spinal motor neurones by the primary motor cortex, and the margin of error indicated by tests utilizing the oscillator must also be considered). However,
Max Velmans Max Velmans (born 27 May 1942 in Amsterdam) is a British psychologist and Emeritus Professor of Psychology at Goldsmiths, University of London, principally known for the theory of consciousness called " reflexive monism". Reflexive monism bridges ...
has argued: "Libet has shown that the experienced intention to perform an act is preceded by cerebral initiation. Why should the experienced decision to veto that intention, or to actively or passively promote its completion, be any different?" In a study published in 2012, Aaron Schurger, Jacobo D. Sitt, and
Stanislas Dehaene Stanislas Dehaene (born May 12, 1965) is a French author and cognitive neuroscientist whose research centers on a number of topics, including numerical cognition, the neural basis of reading and the neural correlates of consciousness. As of 20 ...
proposed that the occurrence of the readiness potentials observed in Libet-type experiments is stochastically occasioned by ongoing spontaneous subthreshold fluctuations in neural activity, rather than an unconscious goal-directed operation. Libet's experiments have received support from other research related to the neuroscience of free will.


Reactions by dualist philosophers

The German philosopher Uwe Meixner commented, "For making an informed decision, the self needs to be conscious of the facts relevant to the decision prior to making the decision; but...the self certainly does not need to be conscious of making the decision at the very same time it makes it...the consciousness of a state of affairs P being (presently) the case is always somewhat later than the actual fact of P's being the case..." When one is speaking to another individual, as a result of the limited velocity of light signals and the limited velocity of sound waves and the limited velocity of nerve signals, what one is experiencing as now is always slightly in the past. No person ever has a definite present awareness of what is occurring around them. There is a small time delay due to the limited velocity of these many different signals that is indiscernible to people because it is extremely short. Meixner also says, "it is hardly surprising that the consciousness of making a decision is no exception to this general rule, which is due to the dependence of consciousness on neurophysiology." Just as nothing that is actually presently there can be observed because of the limited velocity of light but events as they are just a little in the past can be observed, in the same way people do not have a consciousness of their own decisions simultaneously with their making them but they have it undetectedly afterwards. If the mind has the power to think without being causally determined, then all it requires to do in order to make accountable, knowledgeable, free decisions is consciousness of the pertinent facts before its decision making. However, the mind does not require to be aware or conscious of the decision itself at the same it makes that decision. It has been suggested that consciousness is merely a side-effect of neuronal functions, an epiphenomenon of brain states. Libet's experiments are proffered in support of this theory; our reports of conscious instigation of our own acts are, in this view, a mistake of retrospection. However, some dualist philosophers have disputed this conclusion: A more general criticism from a dualist-interactionist perspective has been raised by Alexander Batthyany who points out that Libet asked his subjects to merely "let the urge o moveappear on its own at any time without any pre-planning or concentration on when to act". According to Batthyany, neither reductionist nor non-reductionist agency theories claim that urges which appear on their own are suitable examples of (allegedly) consciously caused events because one cannot passively wait for an urge to occur while at the same time being the one who is consciously bringing it about. Libet's results thus cannot be interpreted to provide empirical evidence in favour of agency reductionism, since non-reductionist theories, even including dualist interactionism, would predict the very same experimental results.


Timing issues

Daniel Dennett Daniel Clement Dennett III (born March 28, 1942) is an American philosopher, writer, and cognitive scientist whose research centers on the philosophy of mind, philosophy of science, and philosophy of biology, particularly as those fields relat ...
argues that no clear conclusion about volition can be derived from Libet's experiment because of ambiguities in the timings of the different events involved. Libet tells when the readiness potential occurs objectively, using electrodes, but relies on the subject reporting the position of the hand of a clock to determine when the conscious decision was made. As Dennett points out, this is only a report of where it ''seems'' to the subject that various things come together, not of the objective time at which they actually occur:


Subjective backward referral or "antedating" of sensory experience

Libet's early theory, resting on study of stimuli and sensation, was found bizarre by some commentators, including
Patricia Churchland Patricia Smith Churchland (born 16 July 1943) is a Canadian-American analytic philosopher noted for her contributions to neurophilosophy and the philosophy of mind. She is UC President's Professor of Philosophy Emerita at the University of Cali ...
, due to the apparent idea of backward causation. Libet argued that data suggested that we retrospectively "antedate" the beginning of a sensation to the moment of the primary neuronal response. People interpreted Libet's work on stimulus and sensation in a number of different ways. John Eccles presented Libet's work as suggesting a backward step in time made by a non-physical mind. Edoardo Bisiach (1988) described Eccles as tendentious, but commented: Libet later concluded that there appeared to be "no ''neural mechanism'' that could be viewed as directly mediating or accounting for" the subjective sensory referrals backward in time (emphasis Libet's). Libet postulated that the primary
evoked potential An evoked potential or evoked response is an electrical potential in a specific pattern recorded from a specific part of the nervous system, especially the brain, of a human or other animals following presentation of a stimulus such as a light f ...
(EP) serves as a "time marker". The EP is a sharp positive potential appearing in the appropriate sensory region of the brain about 25 milliseconds after a skin stimulus. Libet's experiments demonstrated that there is an automatic subjective referral of the conscious experience backwards in time to this time marker. The skin sensation does not enter our conscious awareness until about 500 milliseconds after the skin stimulus, but we subjectively feel that the sensation occurred at the time of the stimulus. For Libet, these subjective referrals would appear to be purely a mental function with no corresponding neural basis in the brain. Indeed, this suggestion can be more broadly generalized:


Conscious mental field theory

In the later part of his career, Libet proposed a theory of the ''conscious mental field'' (CMF) to explain how the mental arises from the physical brain. The two main motivations prompting this proposal were: (1) the phenomenon of the unity of subjective conscious experience and (2) the phenomenon that conscious mental function appears to influence nerve cell activity. Regarding the unity of conscious experience, it was increasingly evident to Libet that many functions of the cortex are localized, even to a microscopic level in a region of the brain, and yet the conscious experiences related to these areas are integrated and unified. We do not experience an infinite array of individual events but rather a unitary integrated consciousness, for example, with no gaps in spatial and colored images. For Libet, some unifying process or phenomenon likely mediates the transformation of localized, particularized neuronal representations into our unified conscious experience. This process seemed to be best accountable in a ''mental sphere'' that appears to emerge from the neural events, namely, the ''conscious mental field''. The CMF is the mediator between the physical activities of nerve cells and the emergence of subjective experience. Thus the CMF is the entity in which unified subjective experience is present and provides the causal ability to affect or alter some neuronal functions. Libet proposed the CMF as a "property" of an emergent phenomenon of the brain; it does not exist without the brain but emerges from the appropriate system of neural activity. This proposal is related to
electromagnetic theories of consciousness The electromagnetic theories of consciousness propose that consciousness can be understood as an electromagnetic phenomenon. Overview Theorists differ in how they relate consciousness to electromagnetism. Electromagnetic ''field'' theories (or " ...
. To test the proposed causal ability of the CMF to affect or alter neuronal functions, Libet proposed an experimental design, which would surgically isolate a slab of cerebral cortex (in a patient for whom such a procedure was therapeutically required). If electrical stimulation of the isolated cortex can elicit an introspective report by the subject, the CMF must be able to activate appropriate cerebral areas in order to produce the verbal report. This result would demonstrate directly that a conscious mental field could affect neuronal functions in a way that would account for the activity of the conscious will. Detailed description of the proposed experimental test is as follows: Libet further elaborated on CMF:


Tributes

Robert W. Doty, professor of Neurobiology and Anatomy at the
University of Rochester The University of Rochester (U of R, UR, or U of Rochester) is a private research university in Rochester, New York. The university grants undergraduate and graduate degrees, including doctoral and professional degrees. The University of ...
: Susan J. Blackmore, visiting lecturer at the
University of the West of England The University of the West of England (also known as UWE Bristol) is a public research university, located in and around Bristol, England. The institution was know as the Bristol Polytechnic in 1970; it received university status in 1992 and ...
,
Bristol Bristol () is a City status in the United Kingdom, city, Ceremonial counties of England, ceremonial county and unitary authority in England. Situated on the River Avon, Bristol, River Avon, it is bordered by the ceremonial counties of Glouces ...
:


In popular culture

Libet and his research into the delay is referenced several times in song titles by musical artist
the Caretaker ''The Caretaker'' is a play in three acts by Harold Pinter. Although it was the sixth of his major works for stage and television, this psychological study of the confluence of power, allegiance, innocence, and corruption among two brothers a ...
, who was influenced by some of his work. The 2011 album ''
An Empty Bliss Beyond This World ''An Empty Bliss Beyond This World'' is the ninth studio album by the Caretaker, an ambient music project of English musician Leyland Kirby, released on 1 June 2011 through History Always Favours the Winners. The record is based on a study rega ...
'' contains a song called "Libet's Delay", which went on to be one of the more popular tracks from it. The Caretaker's final release, ''
Everywhere at the End of Time ''Everywhere at the End of Time'' is the eleventh and final recording by the Caretaker, an alias of English electronic musician Leyland Kirby. Released between 2016 and 2019, its six studio albums use degrading loops of sampled ballroom music ...
'', contains the songs "Back There Benjamin," (Referring to his first name) "Libet's All Joyful Camaraderie" and "Libet Delay", with the latter being a far more twisted, distorted version of the original "Libet's Delay". Also, the 2019 extra album ''
Everywhere, an Empty Bliss ''Everywhere, an Empty Bliss'' is the twelfth and final release by the Caretaker, an alias of English musician Leyland Kirby. Released on February 26, 2019, the record is compiled from archived tracks that were meant to be used on the Caretaker's ...
'' includes a track named "Benjamin Beyond Bliss".


References


Further reading

*Benjamin Libet, Anthony Freeman, and J. K. B. Sutherland, Editors, ''The volitional brain: Towards a neuroscience of free will''. Imprint Academic, 1999. . *Benjamin Libet, ''Mind time: The temporal factor in consciousness'', Perspectives in Cognitive Neuroscience.
Harvard University Press Harvard University Press (HUP) is a publishing house established on January 13, 1913, as a division of Harvard University, and focused on academic publishing. It is a member of the Association of American University Presses. After the retir ...
, 2004. . * Daniel C. Dennett, '' Freedom Evolves''.
Allen Lane Sir Allen Lane (born Allen Lane Williams; 21 September 1902 – 7 July 1970) was a British publisher who together with his brothers Richard and John Lane founded Penguin Books in 1935, bringing high-quality paperback fiction and non-fict ...
, 2003. . * *In his Virtual Nobe
acceptance speech
Libet summarized his life's research and highlighted his work on conscious volitional acts and the antedating of sensory awareness.


External links


Obituary
from ''The Los Angeles Times'', August 27, 2007.
Obituary
from ''The San Francisco Chronicle'', August 18, 2007.

Including video of Libet's acceptance speech. * ttp://www.consciousentities.com/libet.htm Short account of Libet's experiments and theory
Short BBC/Open University animation explaining Liber's experiment
{{DEFAULTSORT:Libet, Benjamin 1916 births 2007 deaths University of California, San Francisco faculty American consciousness researchers and theorists American cognitive neuroscientists People from Chicago University of Chicago alumni People of Ukrainian-Jewish descent Free will