PHENOMENA OF ILLUSORY FORM - CAN WE BRIDGE THE GAP BETWEEN LEVELS OF EXPLANATION

The study of illusory brightness and contour phenomena has become an i mportant tool in modern brain research. Gestalt, cognitive, neural, an d computational approaches are reviewed and their explanatory powers a re discussed in the light of empirical data. Two well-known phenomena of illusory form are dealt with, the Ehrenstein illusion and the Kaniz sa triangle. It is argued that the gap between the different levels of explanation, bottom-up versus top-down, creates scientific barriers w hich have all too often engendered unnecessary debate about who is rig ht and who is wrong. In this review of the literature we favour an int egrative approach to the question of how illusory form is derived from stimulus configurations which provide the visual system with seemingl y incomplete information. The processes that can explain the emergence of these phenomena range from local feature detection to global strat egies of perceptual organisation. These processes may be similar to th ose that help us restore partially occluded objects in everyday vision . To understand better the Ehrenstein and Kanizsa illusions, it is pro posed that different levels of analysis and explanation are not mutual ly exclusive, but complementary. Theories of illusory contour and form perception must, therefore, take into account the underlying neurophy siological mechanisms and their possible interactions with cognitive a nd attentional processes.