Abstract
Gestalt factors such as convexity, closure, and size promote the perception of the direction of figure. Although recent studies have investigated the effects of the individual factors, it has not been clarified how these factors interact with each other, when the features coexist in a local contour. In the present study, we examined psychophysically the interaction of convexity and closure that coexist in a local contour of natural image. First, we established the quantification of convexity and closure (indices to represent the factors) for contours of natural images. By using these quantities, we selected a set of local contours that includes a uniform and wide variation of convexity and closure. Second, we performed a psychophysical experiment to measure the apparent direction of figure for the set of local contours. The result showed that the perceived direction of figure tends to agree with the direction of closure when both convexity and closure coexist in a local contour. The result also showed that while the direction of closure dominates the perception of the direction of figure, the index of closure does not correlate linearly with the perceptual judgment. These results suggest that the perceptual judgment of the direction of figure depends mostly on closure when it coexists with convexity, and that the dependence is dichotomic; two contours with different degrees of closure do not evoke distinct perception. Closure appears to be a dominant and strong cue for the direction of figure.