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Séamas Weech, Daniel Gale, Nikolaus Troje; Interactions between viewing from above and global convexity priors in the interpretation of depth-ambiguous shape-from-contour drawings. Journal of Vision 2015;15(12):736. doi: 10.1167/15.12.736.
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The ‘Viewing from Above’ prior (VFA) guides visual perception of ambiguous stimuli in shape-from-shading and shape-from-contour tasks (Reichel & Todd, 1990). Accordingly, the typical Necker cube tends to be reliably perceived from above, particularly for short presentations, although viewing-from-below is equally valid (e.g., Troje, 2010). Initial observations indicated that shape influences the reliability of the VFA: a ‘diamond’ stimulus (i.e., two attached square-base pyramids) is less likely to be perceived in one consistent orientation. We compared perception of diamond and Necker cube ambiguous line-drawings with four shapes that shared related features: point-up or point-down square-based pyramids and point-up or point-down pyramids attached to a Necker cube. The Necker cube was viewed from above (97%) significantly more often than the diamond (86%). The point-up pyramid was also viewed from above (97%) more often than the point-down pyramid (84%). We also found the point-up pyramid attached to the Necker cube was viewed from above (98%) more often than the same stimulus when inverted (87%). We suggest that a strong VFA prior mediated by a weaker prior for global convexity are generally consistent with the results. The finding contrasts with research that found equal strength for the two priors in shape-from-shading (Langer & Bulthoff, 2001), but supports research on the unequal strength of the two priors in line drawings (Mamassian & Landy, 1998). Specifically, all stimuli tended to be viewed from above; and the point-up and point-down pyramids adhere to a convexity towards the viewer if they are perceived from above and from below, respectively. The same is true for the pyramids attached to Necker cubes. However, the finding that the diamond stimulus is seen less often from above than other stimuli cannot be explained.
Meeting abstract presented at VSS 2015
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