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An afterimage is an image that continues to appear in the eyes after a period of exposure to the original image. An afterimage may be a normal phenomenon (physiological afterimage) or may be pathological (
palinopsia Palinopsia (Greek: ''palin'' for "again" and ''opsia'' for "seeing") is the persistent recurrence of a visual image after the stimulus (psychology), stimulus has been removed. Palinopsia is not a diagnosis, it is a diverse group of pathology, pathol ...
). Illusory palinopsia may be a pathological exaggeration of physiological afterimages. Afterimages occur because photochemical activity in the retina continues even when the eyes are no longer experiencing the original stimulus. The remainder of this article refers to physiological afterimages. A common physiological afterimage is the dim area that seems to float before one's
eye Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light L ...

eye
s after briefly looking into a light source, such as a camera flash. Palinopsia is a common symptom of
visual snow Visual snow, also known as visual static, is an uncommon neurological Neurology (from el, νεῦρον (neûron), "string, nerve" and the suffix -logia, "study of") is a branch of medicine Medicine is the Art (skill), art, science, ...

visual snow
.


Negative afterimages

Negative afterimages are caused when the eye's
photoreceptor
photoreceptor
s, primarily known as rods and
cones A cone is a three-dimensional space, three-dimensional geometric shape that tapers smoothly from a flat base (frequently, though not necessarily, circular) to a point called the Apex (geometry), apex or vertex (geometry), vertex. A cone is fo ...

cones
, adapt to overstimulation and lose sensitivity. Newer evidence suggests there is
cortical Cortex or cortical may refer to: Science Anatomy * Cortex (anatomy), the outermost or superficial layer of an organ * Cortex (hair), the middle layer of a strand of hair * Adrenal cortex, the portion of the adrenal gland that produces cortisol and ...
contribution as well. Normally, the overstimulating image is moved to a fresh area of the retina with small eye movements known as
microsaccade Microsaccades are a kind of fixational eye movement. They are small, jerk-like, involuntary Eye movement (sensory), eye movements, similar to miniature versions of voluntary saccades. They typically occur during prolonged visual fixation (visual) ...
s. However, if the image is large or the eye remains too steady, these small movements are not enough to keep the image constantly moving to fresh parts of the
retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well ...

retina
. The photoreceptors that are constantly exposed to the same stimulus will eventually exhaust their supply of
photopigment Photopigments are unstable pigments that undergo a chemical change when they absorb light. The term is generally applied to the non-protein chromophore A chromophore is the part of a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunnel ...
, resulting in a decrease in signal to the brain. This phenomenon can be seen when moving from a bright environment to a dim one, like walking indoors on a bright snowy day. These effects are accompanied by neural adaptations in the occipital lobe of the brain that function similar to
color balance Color (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. Currently, American English ...
adjustments in photography. These adaptations attempt to keep vision consistent in dynamic lighting. Viewing a uniform background while these adaptations are still occurring will allow an individual to see the afterimage because localized areas of vision are still being processed by the brain using adaptations that are no longer needed. The Young-Helmholtz trichromatic theory of color vision postulated that there were three types of photoreceptors in the eye, each sensitive to a particular range of visible light: short-wavelength cones, medium-wavelength cones, and long-wavelength cones. Trichromatic theory, however, can not explain all afterimage phenomena. Specifically, afterimages are the complementary hue of the adapting stimulus, and trichromatic theory fails to account for this fact. Originally published as: The failure of trichromatic theory to account for afterimages indicates the need for an opponent-process theory such as that articulated by
Ewald Hering Karl Ewald Konstantin Hering (5 August 1834 – 26 January 1918) was a German physiologist Physiology (; ) is the scientific study of Function (biology), functions and mechanism (biology), mechanisms in a life, living system. As a Branches ...

Ewald Hering
(1878) and further developed by Hurvich and Jameson (1957). The
opponent process 360px, Diagram of the opponent process The opponent process is a color theory that states that the human visual system interprets information about color by processing signals from cone cells and rod cells in an antagonistic manner. There is so ...
theory states that the human
visual system The visual system comprises the sensory organ A sense is a biological system A biological system is a complex network which connects several biologically relevant entities. Biological organization spans several scales and are determined b ...
interprets color information by processing signals from cones and rods in an antagonistic manner. The opponent color theory suggests that there are three opponent channels: red versus green, blue versus yellow, and black versus white. Responses to one color of an opponent channel are antagonistic to those of the other color. Therefore, a
green Green is the between and on the . It is evoked by light which has a of roughly 495570 . In systems, used in painting and color printing, it is created by a combination of yellow and ; in the , used on television and computer screens, ...

green
image will produce a
magenta Magenta () is a color that is variously defined as purplish-red, reddish-purple Purple refers to any of a variety of colors with hue between red and blue. Purple is closely associated with Violet (color), violet. In optics, purple and vi ...

magenta
afterimage. The green color fatigues the green photoreceptors, so they produce a weaker signal. Anything resulting in less green, is interpreted as its paired primary color, which is magenta, i.e. an equal mixture of red and blue. Example movie which produces distortion illusion after one watches it and looks away. See
Motion aftereffect The motion aftereffect (MAE) is a visual illusion experienced after viewing a moving visual stimulation, stimulus for a time (tens of milliseconds to minutes) with stationary eyes, and then fixating a stationary stimulus. The stationary stimulus a ...
.


Positive afterimages

Positive afterimages, by contrast, appear the same color as the original image. They are often very brief, lasting less than half a second. The cause of positive afterimages is not well known, but possibly reflects persisting activity in the
brain A brain is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tiss ...

brain
when the
retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well ...

retina
l
photoreceptor cell A photoreceptor cell is a specialized type of neuroepithelial cellNeuroepithelial cells, or neuroectodermal cells, form the wall of the closed neural tube in early embryonic development ''Embryonic'' is the twelfth studio album by experimenta ...

photoreceptor cell
s continue to send neural impulses to the
occipital lobe The occipital lobe is one of the four major lobes of the 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. The cerebral cortex m ...

occipital lobe
. A stimulus which elicits a positive image will usually trigger a negative afterimage quickly via the adaptation process. To experience this phenomenon, one can look at a bright source of light and then look away to a dark area, such as by closing the eyes. At first one should see a fading positive afterimage, likely followed by a negative afterimage that may last for much longer. It is also possible to see afterimages of random objects that are not bright, only these last for a split second and go unnoticed by most people.


On empty shape

An afterimage in general is an optical illusion that refers to an image continuing to appear after exposure to the original image has ceased. Prolonged viewing of the colored patch induces an afterimage of the
complementary color Complementary colors are pairs of color Color (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to ...
(for example, yellow color induces a bluish afterimage). The "afterimage on empty shape" effect is related to a class of effects referred to as
contrast effectA contrast effect is the enhancement or diminishment, relative to normal, of perception, cognition or related performance as a result of successive (immediately previous) or simultaneous exposure to a stimulus (physiology), stimulus of lesser or grea ...
s. In this effect, an empty (white) shape is presented on a colored background for several seconds. When the background color disappears (becomes white), an illusionary color similar to the original background is
perceived Perception (from the Latin ''perceptio'', meaning gathering or receiving) is the organization, identification, and interpretation of Sense, sensory information in order to represent and understand the presented information or environment. ...
within the shape. The mechanism of the effect is still unclear, and may be produced by one or two of the following mechanisms: *During the presentation of the empty shape on a colored background, the colored background induces an illusory complementary color ("induced color") inside the empty shape. After the disappearance of the colored background an afterimage of the "induced color" might appear inside the "empty shape". Thus, the expected color of the shape will be complementary to the "induced color", and therefore similar to the color of the original background. *After the disappearance of the colored background, an afterimage of the background is induced. This induced color has a complementary color to that of the original background. It is possible that this background afterimage induces simultaneous contrast on the "empty shape". Simultaneous contrast is a psychophysical phenomenon of the change in the appearance of a color (or an achromatic stimulus) caused by the presence of a surrounding average color (or luminance).


Gallery

File:US flag(inverted).svg, The
US flag The flag of the United States of America, often referred to as the American flag or the U.S. flag, is the national flag of the United States. It consists of thirteen equal horizontal stripes of red (top and bottom) alternating with white, with ...

US flag
inverted File:ItalianFlagInverted.gif, The
Italian flag The flag of Italy ( it, Bandiera d'Italia, ), often referred to in Italian as ''il Tricolore'' ( en, the Tricolour, ), is the national flag of Italy Italy ( it, Italia ), officially the Italian Republic ( it, Repubblica Italiana, links=no ...

Italian flag
inverted


See also

*''
Book of Optics The ''Book of Optics'' ( ar, كتاب المناظر, Kitāb al-Manāẓir; la, De Aspectibus or ''Perspectiva''; it, Deli Aspecti) is a seven-volume treatise on optics Optics is the branch of physics Physics (from grc, φυσι ...
'' *
Emmert's lawEmmert's law states that objects that generate retina, retinal images of the same size will look different in physical size (linear size) if they appear to be located at different distances. Specifically, the ''perceived linear size'' of an object in ...
*
Lilac chaser The lilac chaser is a visual illusion, also known as the Pac-Man illusion. It consists of 12 lilac (color), lilac (or pink, rose (color), rose, or magenta), blurred discs arranged in a circle (like the numbers on a clock), around a small black, c ...
* McCollough effect *
Motion aftereffect The motion aftereffect (MAE) is a visual illusion experienced after viewing a moving visual stimulation, stimulus for a time (tens of milliseconds to minutes) with stationary eyes, and then fixating a stationary stimulus. The stationary stimulus a ...
*
Neural adaptationNeural adaptation or sensory adaptation is a gradual decrease over time in the responsiveness of the sensory system The sensory nervous system is a part of the nervous system responsible for processing sensory information. A sensory system con ...
*
Palinopsia Palinopsia (Greek: ''palin'' for "again" and ''opsia'' for "seeing") is the persistent recurrence of a visual image after the stimulus (psychology), stimulus has been removed. Palinopsia is not a diagnosis, it is a diverse group of pathology, pathol ...
*
Persistence of vision Persistence of vision traditionally refers to the optical illusion that occurs when visual perception of an object does not cease for some time after the rays of light proceeding from it have ceased to enter the eye. The illusion has also been des ...
*
Screen burn-in Screen or Screens may refer to: Arts * Screen printing Screen printing is a printing technique where a mesh is used to transfer ink onto a Substrate (printing), substrate, except in areas made impermeable to the ink by a blocking stencil. A ...
*'' Spectropia'' *
Visual perception Visual perception is the ability to interpret the surrounding environment (biophysical), environment through photopic vision (daytime vision), color vision, scotopic vision (night vision), and mesopic vision (twilight vision), using light in ...


Notes


External links


The Palinopsia Foundation is dedicated to increasing awareness of palinopsia, to funding research into the causes, prevention and treatments for palinopsia, and to advocating for the needs of individuals with palinopsia and their families.Eye On Vision Foundation raises money and awareness for persistent visual conditions
a small demonstration.

{{Visual phenomena
Optical illusions An optical illusion is any illusion An illusion is a distortion of the senses, which can reveal how the human brain The human brain is the central organ (anatomy), organ of the human nervous system, and with the spinal cord makes up the ...
Vision Articles containing video clips