Color Phi Phenomenon

The color phi phenomenon is a perceptual illusion, first documented by the psychologists Paul Kolers and Michael von Grünau, in which a more elaborate version of the ordinary phi phenomenon causes the color of an apparently moving object to change abruptly partway along its perceived path of motion. In the basic experimental demonstration, viewers are shown two images presented one after another in sequence, a blue dot appearing first near the top of the display followed by a red dot appearing near the bottom; under the right conditions of timing and spacing between the two dots, viewers perceive a single dot moving continuously from the first position to the second, but they also report that the moving dot changes from blue to red partway through its perceived trajectory, before the second, red dot has actually been presented to them. The philosopher Daniel Dennett has used the color phi phenomenon to challenge a view of consciousness he calls Cartesian materialism, arguing that because observers report experiencing the color change occurring before the red dot is physically shown, yet cannot truly be perceiving a stimulus that has not yet appeared, the phenomenon raises fundamental questions about the relationship between perception, consciousness and the neural processing that produces subjective experience.