Cues for Edge and the Origin of Illusory Contours: An Alternative Approach

Abstract

In perception objects are characterized by numerous properties, including surfaces and edges, texture and pattern, solidity and depth, and lightness and color. They can also be characterized by opacity, translucency, or transparency. These properties are signaled by what in accord with traditional usage can be called cues. Thus object depth is signaled by retinal disparity, motion parallax, vergence and accommodation, and various “pictorial” cues such as linear perspective, overlay, and elevation in the visual field. Of greatest relevance here is the contrivance of cues by various forms of artifice to convey the appearance of an object property where none exists physically. For example, retinal disparity can be contrived by means of two-dimensional stereograms viewed in a stereoscope. The outcome in perception is a compelling appearance of depth when none is present in the distal stimulus array. Similarly, linear perspective and overlay can be effectively contrived by means of drawing and photography to convey the appearance of depth in pictures and photographs.