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Tadamasa Sawada, Mary A. Peterson; The role of symmetry and volume in figure-ground organization. Journal of Vision 2010;10(7):1170. doi: https://doi.org/10.1167/10.7.1170.
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Many objects in our environment are symmetrical and volumetric. These two constraints are extremely effective in 3D shape recovery (Sawada, 2009). In contrast, the spaces between objects, representing the background, are almost never symmetrical and volumetric. Prior studies of figure-ground organization showed that symmetrical regions are perceived to be figures only slightly (albeit significantly) more often than expected by chance Salvagio, Mojica & Peterson, 2008). In this study we examine the hypothesis that the addition of volume enhances the likelihood of seeing symmetrical regions as figures. Experiment. If the observer perceives a given region in a stimulus as a figure (object), then she should be able to recognize the shape of the region; at the same time, we don't expect the observer to be able to recognize the shape of the background (Rubin, 1915). We tested human performance on a shape-matching task using signal detection analysis methods. On each trial, the observer was shown two stimuli one after the other. Each stimulus was composed of several regions horizontally aligned. The viewing duration was 500 ms for each stimulus. A mask was shown for 500 ms between the stimuli. The observer's task was to memorize the shapes of the specified regions in the first stimulus and to judge whether or not the shapes of the regions in the second stimulus were identical to the memorized shapes. The shapes of the regions were controlled to be either symmetrical or asymmetrical. The volumes of the regions were controlled by using the depth cue of surface-contour. The results suggest that it is easier to recognize the shape of regions that are both symmetrical and volumetric. We conclude that perceptual assignment of which regions are figures depends on the presence of 3D symmetry.
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