Illusions Gallery
There are a number of reasons to present a Gallery of Illusions.
My first objective for these pages will be to present some illusory stimuli which are fun to view. As time permits, I will add hypertext and graphical material relevant to my research and to students who are studying sensation, perception or research methods.
Some Terms and Definitions
Illusions in visual perception occur when experiences, which people report, do not correspond to physical measurements of stimuli. People are often surprised when they become aware of the lack of correspondence.
Correspondence between people's reports and the physical characteristics of stimuli is assessed through the methods of psychophysics. In psychophysics, stimuli are classified as either proximal or distal. Proximal refers to the patterns of energy impinging on receptors. Distal refers to the patterns of energy that emanate from objects.
Our computational brains abstract from neural signals generated in response to proximal stimuli, but products resulting from the abstractions must correspond with the distal stimulus for us to have veridical experiences. If you are sitting in a room with an open door, it is likely that door is swung inward toward you. The pattern of stimulation on each of your curved retinas is a trapezoid curved in the x, y, & z-dimensions, but the door shape is rectangular. You see the door as rectangular even when the proximal stimulus has a distorted trapezoidal pattern. This is an example of what psychophysicists call shape constancy.
Humans would not have successfully adapted to survive and thrive in the environment of earth if there were not psychophysical correspondence between distal stimuli and most experiences. Illusions are instances which lack correspondence and these instances can be very informative in helping us to understand how we are structured, how we function, and how we can best represent the world around us.
Illusions Links