McCollough effect
Encyclopedia
Visual perception
Visual perception is the ability to interpret information and surroundings from the effects of visible light reaching the eye. The resulting perception is also known as eyesight, sight, or vision...
in which colorless grating
Grating
A grating is any regularly spaced collection of essentially identical, parallel, elongated elements. Gratings usually consist of a single set of elongated elements, but can consist of two sets, in which case the second set is usually perpendicular to the first...
s appear colored depending on (contingent
Contingent perceptual aftereffect
Contingent aftereffects are studied in human perception and can be defined as illusory percepts that are apparent on a test stimulus after exposure to an induction stimulus for an extended period. Contingent aftereffects can be contrasted with simple aftereffects, the later requiring no test...
on) the orientation
Orientation (geometry)
In geometry the orientation, angular position, or attitude of an object such as a line, plane or rigid body is part of the description of how it is placed in the space it is in....
of the gratings. It is an aftereffect requiring a period of induction
Neural adaptation
Neural adaptation or sensory adaptation is a change over time in the responsiveness of the sensory system to a constant stimulus. It is usually experienced as a change in the stimulus. For example, if one rests one's hand on a table, one immediately feels the table's surface on one's skin. Within a...
to produce it. For example, if someone alternately looks at a red horizontal grating and a green vertical grating for a few minutes, a black-and-white horizontal grating will then look greenish and a black-and-white vertical grating will then look pinkish. The effect was discovered by Celeste McCollough
Celeste McCollough
Celeste McCollough, known since about 1996 as Celeste McCollough Howard is an American scientist who conducts research in human visual perception. She is famous for discovering, in 1965, the first contingent aftereffect, known soon after as the McCollough effect...
in 1965.
Producing the effect
To obtain the effect, first look at a test image similar to that at top right. It should contain oppositely oriented gratings of linesLine (mathematics)
The notion of line or straight line was introduced by the ancient mathematicians to represent straight objects with negligible width and depth. Lines are an idealization of such objects...
, such as horizontal and vertical as shown here. Next, stare
Staring
Staring is a prolonged gaze or fixed look. In staring, one object or person is the continual focus of visual interest, for an amount of time. Staring can be interpreted as being either hostile, or the result of intense concentration or affection. Staring behaviour can be considered a form of...
alternately at two induction images similar to the ones directly beneath the top image. One image should show one orientation of grating (here horizontal) with a coloured background (red) and the other should show the other orientation of grating (here vertical) with a different, preferably oppositely coloured
Complementary color
Complementary colors are pairs of colors that are of “opposite” hue in some color model. The exact hue “complementary” to a given hue depends on the model in question, and perceptually uniform, additive, and subtractive color models, for example, have differing complements for any given color.-...
background (green). Each image should be gazed at for several seconds at a time, and the two images should be gazed at for a total of several minute
Minute
A minute is a unit of measurement of time or of angle. The minute is a unit of time equal to 1/60th of an hour or 60 seconds. In the UTC time scale, a minute on rare occasions has 59 or 61 seconds; see leap second. The minute is not an SI unit; however, it is accepted for use with SI units...
s for the effect to become visible. Stare approximately at the centre of each image, allowing the eyes to move around a little. After several minutes, look back to the test image; the gratings should appear tinted by the opposite colour to that of the induction gratings (i.e., horizontal should appear greenish and vertical pinkish).
Properties of the effect
The McCollough effect is remarkable because it is long lasting. McCollough originally reported that these aftereffects may last for an hour or more. They can last much longer than that, however. Jones and Holding (1975) found that 15 minutes of induction can lead to an effect lasting 3 months.The effect is different from colored afterimage
Afterimage
An afterimage or ghost image or image burn-in is an optical illusion that refers to an image continuing to appear in one's vision after the exposure to the original image has ceased...
s, which appear superimposed on whatever is seen and which are quite brief. It depends on retinal orientation (tilting the head by 45 degrees makes the colors in the above example disappear; tilting the head by 90 degrees makes the colors reappear such that the gravitationally vertical grating now looks green), and because inducing the effect with one eye leads to no effect being seen with the other eye. However, there is some evidence of binocular interactions.
Any aftereffect requires a period of induction (or adaptation
Neural adaptation
Neural adaptation or sensory adaptation is a change over time in the responsiveness of the sensory system to a constant stimulus. It is usually experienced as a change in the stimulus. For example, if one rests one's hand on a table, one immediately feels the table's surface on one's skin. Within a...
) with an induction stimulus (or, in the case of the McCollough effect, induction stimuli). It then requires a test stimulus on which the aftereffect can be seen. In the McCollough effect as described above, the induction stimuli are the red horizontal grating and the green vertical grating. A typical test stimulus might show adjacent patches of black-and-white vertical and horizontal gratings (as above). The McCollough-effect colours are less saturated
Saturation (color theory)
In colorimetry and color theory, colorfulness, chroma, and saturation are related but distinct concepts referring to the perceived intensity of a specific color. Colorfulness is the degree of difference between a color and gray. Chroma is the colorfulness relative to the brightness of another color...
than the induction colours.
The induction stimuli can have any different colors. The effect is strongest, however, when the colors are complementary
Complementary color
Complementary colors are pairs of colors that are of “opposite” hue in some color model. The exact hue “complementary” to a given hue depends on the model in question, and perceptually uniform, additive, and subtractive color models, for example, have differing complements for any given color.-...
, such as red and green, and blue and orange. A related version of the McCollough effect also occurs with a single color and orientation. For example, induction with only a red horizontal grating makes a black-and-white horizontal test grating appear greenish whereas a black-and-white vertical test grating appears colourless (although there is some argument about that). Stromeyer (1978) called these non-redundant effects. According to him, the classic effect with induction from two different orientations and colours simply makes the illusory colors more noticeable via contrast
Contrast effect
A contrast effect is the enhancement or diminishment, relative to normal, of perception, cognition and related performance as a result of immediately previous or simultaneous exposure to a stimulus of lesser or greater value in the same dimension...
.
The effect is specific to the region of the retina that is exposed to the induction stimuli. This has been shown by inducing opposite effects in adjacent regions of the retina (i.e., from one region of the retina verticals appear pink and horizontals appear greenish; from an adjacent region of the retina, verticals appear greenish and horizontals appear pink). Nevertheless, if a small region of the retina is exposed to the induction stimuli, and the test contours run through this region, the effect spreads along those test contours. Of course, if the induced area is in the fovea
Fovea
The fovea centralis, also generally known as the fovea , is a part of the eye, located in the center of the macula region of the retina....
(central vision) and the eyes are allowed to move, then the effect will appear everywhere in the visual scene visited by the fovea.
The effect is also optimal when the thickness of the bars in the induction stimulus matches that of those in the test stimulus (i.e., the effect is tuned, albeit broadly, to spatial frequency
Spatial frequency
In mathematics, physics, and engineering, spatial frequency is a characteristic of any structure that is periodic across position in space. The spatial frequency is a measure of how often sinusoidal components of the structure repeat per unit of distance. The SI unit of spatial frequency is...
). This property led to non-redundant effects being reported by people who had used computer monitors with uniformly colored phosphor
Phosphor
A phosphor, most generally, is a substance that exhibits the phenomenon of luminescence. Somewhat confusingly, this includes both phosphorescent materials, which show a slow decay in brightness , and fluorescent materials, where the emission decay takes place over tens of nanoseconds...
s to do word processing
Word processing
Word processing is the creation of documents using a word processor. It can also refer to advanced shorthand techniques, sometimes used in specialized contexts with a specially modified typewriter.-External links:...
. These monitors were popular in the 1980s, and commonly showed text as green on black. People noticed later when reading text of the same spatial frequency, in a book say, that it looked pink. Also a horizontal grating of the same spatial frequency as the horizontal lines of the induction text (such as the horizontal stripes on the letters "IBM" on the envelope for early floppy disk
Floppy disk
A floppy disk is a disk storage medium composed of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic carrier lined with fabric that removes dust particles...
s) looked pink.
A variety of similar aftereffects have been discovered not only between pattern and colour contingencies, but between movement/colour, spatial frequency/colour and other relationships. All such effects may be referred to as McCollough Effects or MEs.
Explanations of the effect
McCollough's paper sparked hundreds of scientific papers on the effect.Explanations of the McCollough effect appear to fall in to three camps. McCollough indicated colour adaptation of edge sensitive neurons in lower, monocular
Monocular
A monocular is a modified refracting telescope used to magnify the images of distant objects by passing light through a series of lenses and sometimes prisms; the use of prisms results in a lightweight telescope. Volume and weight are less than half those of binoculars of similar optical...
regions of the visual cortex
Visual cortex
The visual cortex of the brain is the part of the cerebral cortex responsible for processing visual information. It is located in the occipital lobe, in the back of the brain....
.
A functional
Functional
Generally, functional refers to something able to fulfill its purpose or function.*Functionalism and Functional form, movements in architectural design*Functional group, certain atomic combinations that occur in various molecules, e.g...
explanation of MEs has been posited in the form of an error-correcting device (ECD) whose purpose is to maintain an accurate internal representation of the external world. Consistent pairings of colour and oriented lines are not found frequently in natural environments, thus consistent pairing may indicate pathology of the eye. An ECD might compensate for such pathology
Pathology
Pathology is the precise study and diagnosis of disease. The word pathology is from Ancient Greek , pathos, "feeling, suffering"; and , -logia, "the study of". Pathologization, to pathologize, refers to the process of defining a condition or behavior as pathological, e.g. pathological gambling....
by adjusting the appropriate neurons to a neutral point in adaptation to orientation contingent colour.
A third explanation points to the contribution of classical conditioning
Classical conditioning
Classical conditioning is a form of conditioning that was first demonstrated by Ivan Pavlov...
to normal homeostatic regulation. MEs are explained by the same mechanisms as pharmacological withdrawal symptoms, thus the “pharmacological CR is expressed as pharmacological adaptation (tolerance) in the presence of the drug, and withdrawal symptoms in the absence of the drug” and the “chromatic CR is expressed as chromatic adaptation in the presence of colour, and the ME in the absence of colour”. By this account MEs are of no adaptive value, but have been selected for as a domain-general ability to anticipate events. This is related to Opponent-process theory
Opponent-process theory
Opponent-process theory is a universal psychological and neurological model proposed by Ewald Hering to account for a wide range of behaviors including color vision; this model was expanded by his co-worker at the University of Pennsylvania, Richard Solomon, to explain addictive and emotional...
.
It is worth noting that these theories do not predict or explain the Anti-McCollough Effect.
Neurophysiological explanations of the effect have variously pointed to the adaptation of cells in the lateral geniculate nucleus
Lateral geniculate nucleus
The lateral geniculate nucleus is the primary relay center for visual information received from the retina of the eye. The LGN is found inside the thalamus of the brain....
designed to correct for chromatic aberration
Chromatic aberration
In optics, chromatic aberration is a type of distortion in which there is a failure of a lens to focus all colors to the same convergence point. It occurs because lenses have a different refractive index for different wavelengths of light...
of the eye, to adaptation of cells in the visual cortex
Visual cortex
The visual cortex of the brain is the part of the cerebral cortex responsible for processing visual information. It is located in the occipital lobe, in the back of the brain....
jointly responsive to color and orientation (this was McCollough's explanation) such as monocular areas of cortical hypercolumns, to processing within higher centers of the brain (including the frontal lobes), and to learning
Learning
Learning is acquiring new or modifying existing knowledge, behaviors, skills, values, or preferences and may involve synthesizing different types of information. The ability to learn is possessed by humans, animals and some machines. Progress over time tends to follow learning curves.Human learning...
and memory
Memory
In psychology, memory is an organism's ability to store, retain, and recall information and experiences. Traditional studies of memory began in the fields of philosophy, including techniques of artificially enhancing memory....
. In 2006, the explanation of the effect was still the subject of debate, although there was a consensus in favour of McCollough's original explanation.
MEs do not transfer interocularly and from this it seems reasonable to deduce that the effect occurs in an area of the visual system prior to V1-4B, where binocular cells first occur.
The Anti-McCollough Effect
Recently, a new effect in the opposite direction of the McCollough effect was discovered and has been termed the anti-McCollough effect. This effect may be induced by alternating pairings of gratings in parallel alignment, one achromatic (black and white) and the other black and a single colour (say black and red). If the colour used was red, then after the induction phase the achromatic grating appeared slightly red. This effect is distinct from the classical effect in three important regards; the perceived colour of the aftereffect is the same as the inducer's colour, the perceived colour of the aftereffect is weaker than the classical effect, and the aftereffect shows complete interocular transfer. Like the classic effect, the anti-McCollough effect (AME) is long lasting. Despite producing a less saturated illusory colour, the induction of an AME may override a previously induced ME.Given that AMEs do transfer interocularly it is reasonable to suppose that they must occur in higher, binocular regions of the brain. Despite producing a less saturated illusory colour, the induction of an AME may override a previously induced ME, providing additional weight to the argument that AMEs occur in the higher visual areas than MEs.
Explanations of the effect by adaptation of edge-detectors, functional ECDs, and classical conditioning are compelling but will have to be adjusted for the inclusion of AMEs.