Bordering a shadow, a line's negative contour diminishes shape-from-shadow perception.
Published: 2005
Language: eng
Number of pages: 95
Description: Experiment 2 is a stepping-stone experiment preparing the way for Experiment 3. It tested whether the dotted shadows to be used in Experiment 3 can show the Mooney face. Results of Experiment 2 also supported the border-polarity hypothesis in that positive border polarity (from an averaged-dark dotted shadowed area to a light illuminated area) revealed the face.Ewald Hering demonstrated that an especially dark line coinciding with a shadow border made the shadow look like a stain. Hering attributed the loss in shadow perception to the loss of penumbra (the gradual change at a luminance border). However, it may be the direction of luminance change, or 'polarity,' of the dark line's contour bordering the shadowed region that diminished shadow perception---a border-polarity hypothesis. Alternatively, the loss may be due to an increase in the number of contours (the line has two contours, the shadow just one), or belongingness (inappropriately, the line's contour may belong to one of the large regions in the stimulus).Experiment 3 used depth in a binocular percept to split the dotted shadowed region into two surface planes without modifying border polarity. The border-polarity hypothesis predicts that as long as the border polarity is positive, stereo depth should not affect shape-from-shadow perception. The belongingness hypothesis predicts that the inappropriate belongingness signaled by stereo depth should impair shape-from-shadow perception. Experiment 3's results discount belongingness and support border-polarity.Finally, Experiment 4 took up Hering's idea of gradual change. Its results suggest shape-from-shadow vision may be sensitive to graded border polarity in the following way: the darker the line with negative border polarity the more shape-from-shadow-perception is diminished.Experiment 1 used a 'Mooney face,' which has shadows without penumbras. It found that a light, gray line coinciding with the border of a dark shadow allowed perception of the shape-from-shadowed-face, whereas a dark line bordering a light shadow blocked face perception. Experiment 1's results counter the number-of-contours hypothesis, and support the border-polarity account. They also discount an argument that if the shadowed region is darker than the illuminated region, the face will be seen.
Notes: Thesis (Ph.D.)--University of Toronto, 2005.

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Source: Dissertation Abstracts International, Volume: 66-06, Section: B, page: 3448.