The Nature of, Perceptual Illusions

Abstract

Perceptual illusions are defined as consistent and persistent discrepancies between a physial state of affairs and its representation in consciousness. It is argued that for the most part these discrepancies occur mainly as a consequence of the activation of perceptual processes by contrived, artificial stimuli. When activated by their normal or natural stimuli the processes result in veridical perception. When activated by artificial or unnatural stimuli the same processes result frequently in nonveridical, illusory, perception. Thus illusions provide a means for isolating and investigating the sensory and cognitive processes associated with normal perception. A number of independent classes of perceptual illusion – induced depth by stereopsis, intersecting-line effects, object-field and component-object illusions, induced contrast effects and illusory contours – are here described and analysed.