School of Psychology, Bangor University, Bangor, UK.
Department of Cognitive and Brain Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel; Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, Beer-Sheva, Israel.
Cognition. 2021 Jul;212:104664. doi: 10.1016/j.cognition.2021.104664. Epub 2021 Mar 18.
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.
阴影的 2D 图像通常会由于阴影信息和对光源位置的假设而产生深度错觉。具体来说，顶部较亮的 2D 图像通常呈现出凸面，而顶部较暗的图像通常呈现出凹面，反映了来自上方的光的假设。恢复阴影图像的 3D 形状的过程称为从阴影中恢复形状。在这里，我们检查了瞳孔是否对阴影形状的深度错觉做出反应。在三个实验中，我们表明瞳孔大小受到深度知觉的影响，因此当参与者感知到刺激是凹面时，瞳孔会比感知到凸面时扩张得更大。这种情况仅在参与者对刺激的形状做出判断或在他们被动观看但意识到不同形状时发生。如果参与者没有意识到错觉，在被动观看时，瞳孔大小没有差异，这表明从阴影中恢复形状的某些方面需要注意力。所有刺激都是等照度的，深度知觉是通过操纵阴影的方向来产生的，因此瞳孔大小的变化不能归因于图像中光的数量变化。我们假设（并在行为控制实验中证实了这一点），由于“较暗的是更深的”启发式，深度知觉会转化为对黑暗的主观知觉，并且得出结论，瞳孔的生理反应反映了对光的主观知觉。
