The McCollough effect is a phenomenon of human visual perception in which colorless gratings appear colored contingent on the orientation of the gratings. It is an aftereffect requiring a period of induction 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 is remarkable for often lasting an hour or more, and in some cases after prolonged exposure to the grids, the effect can last up to 3.5 months. The effect was discovered by American psychologist Celeste McCollough in 1965. (Wikipedia)
A test image for the McCollough effect:
On first looking at this image, the vertical and horizontal lines should look black and white, colorless. After induction (see the red and green images), the space between vertical lines should look reddish and the space between horizontal lines should look greenish.
An induction image for the McCollough effect.
Stare at the center of red image for a few seconds, then at the center of the green image for a few seconds. Then return to red image. Keep looking between the two colored images for at least 3 minutes.
When steadily fixating the central dot for many seconds, the peripheral annulus will fade and will be replaced by the colour or texture of the background.
If you concentrate your eyes on the black dot, you’ll experience the disappearance of the blue surfaces.
Troxler's fading, or the Troxler Effect, is an optical illusion affecting visual perception. When one fixates on a particular point for even a short period of time, an unchanging stimulus away from the fixation point will fade away and disappear. Recent research suggests that at least some portion of the perceptual phenomenon associated with Troxler's fading occurred in the brain. .
Troxler's fading was first identified by Ignaz Paul Vital Troxler in 1804.(Wikipedia)
The figure is a demonstration of Troxler's effect. To experience it, fixate precisely on the red spot, while paying attention to the bluish annulus. After a few seconds of careful fixation, the annulus will disappear, and the red spot will appear to be surrounded by a completely white field. Movements of the eyes will immediately bring the blue annulus back to perception. (www.nature.com)
In this example, the spots in the "lilac chaser" illusion fade away after several seconds when the black cross is stared at long enough. This leaves a grey background and the cross. Some viewers may notice that the moving space has faded into a moving blue-green spot, possibly with a short trail following it. Furthermore, moving one's eyes away from the image after a period of time may result in a brief, strong afterimage of a circle of green spots.. (Wikipedia)