In the first part of the lecture several meanings of the term “perceptual grouping” as it applies to contour and texture will be distinguished, especially grouping as segregation and grouping as cohesion. This will be expanded to a discussion of the segregation of surfaces in depth and the occlusion cues on which this is based, which also underlie the perception of “subjective contours”. Special attention will be given to the way pictorial cues interact with binocular stereopsis to influence perceived surface occlusion. Finally, the depiction of occlusion will be discussed as a major feature of art, with support for Kanizsa’s view that this is a perceptual not a conceptual achievement. As such I show that surface segregation can fail perceptually even when the conceptual intention is clear.
