Top-down effect on pupillary response: Evidence from shape from shading

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