Sapir, Ayelet, Hershman, Ronen and Henik, Avishai (2021) Top-down effect on pupillary response: evidence from shape from shading. Cognition, 212:104664. ISSN 0010-0277 (Print), 1873-7838 (Online) (doi:10.1016/j.cognition.2021.104664)

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Abstract

Shaded 2D images often create an illusion of depth, due to the shading information and assumptions regarding the location of the light source. Specifically, 2D images that are lighter on top usually appear convex while images that are darker on top, usually appear concave, reflecting the assumption that light is coming from above. The process of recovering the 3D shape of a shaded image is called Shape from Shading. Here we examined whether the pupil responds to the illusion of depth in a shape from shading task. In three experiments we show that pupil size is affected by the percept of depth, so that it dilates more when participants perceive the stimulus as concave, compared to when they perceive it as convex. This only happens if participants make a judgment regarding the shape of the stimulus or when they view it passively but are aware of the different shapes. No differences in pupil size were found with passive viewing if participants were not aware of the illusion, suggesting that some aspects of shape from shading require attention. All stimuli were equiluminant, and the percept of depth was created by manipulating the orientation of the shading, so that changes in pupil size could not be accounted by changes in the amount of light in the image. We posit, and confirmed it in a behavioral control experiment, that the perception of depth is translated to a subjective perception of darkness, due to the “darker is deeper” heuristic and conclude that the pupillary physiological response reflects the subjective perception of light.

Item Type:	Article
Uncontrolled Keywords:	pupillometry, pupil light reflex, shape from shading, depth perception, illusion
Subjects:	B Philosophy. Psychology. Religion > BF Psychology Q Science > Q Science (General)
Faculty / School / Research Centre / Research Group:	Faculty of Education, Health & Human Sciences Faculty of Education, Health & Human Sciences > Institute for Lifecourse Development Faculty of Education, Health & Human Sciences > School of Human Sciences (HUM)
Last Modified:	25 Mar 2025 15:16
URI:	http://gala.gre.ac.uk/id/eprint/50102

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