Subjective contours and apparent depth: a direct test.

however, explains such secondary effects associated with subjective contours as changes in brightness or in apparent depth. In contradistinction to the physiological explanations are a number of hypotheses that are primarily cognitive in nature. Kanizsa (1976) maintains that illusory contours are merely an unusually strong example of the Gestalt principle of closure. Other theorists suggest, rather, that subjective contours emerge as some form of unconscious inference on the partial figural cues present in the inducing array, in much the same way as meaning is abstracted from incomplete outline drawings or cartoons (Bradley & Dumais, 1975; Gregory, 1972; Kennedy, 1976; Piggins, 1975; Rock and Anson, 1979). Coren (1972) has offered an alternative cognitive theory. He suggested that subjective contours result from the organization of the percept around implicit depth cues in the two-dimensional array, and offered demonstrations of the creation of subjective contours by the manipulation of depth cues. Halpern (1981) showed a manifest depth component by having subjects reproduce the apparent depth separation between a subjective contour and its background on a two-dimensional horizontal line. In indirect tests, c c