Abstract
One of the earliest reported visual aftereffects is the shape aftereffect, in which looking at a particular shape can make subsequent shapes seem distorted in the "opposite" direction. After viewing a narrow ellipse, for example, a perfect circle can look like a broad ellipse. It is generally thought that shape aftereffects are determined by the retinal dimensions of successive shapes. However, perceived shape is invariant for the large changes in retinal image resulting from different viewing angles, raising the previously untested question of whether shape aftereffects are determined by the dimensions of retinal shapes or perceived shapes. By viewing adaptors from an angle, with subsequent fronto-parallel tests, we establish that shape aftereffects are not solely determined by the dimensions of successive retinal images. Moreover, by comparing adaptation to the same retinal shape with and without stereo surface-slant cues, we show that shape aftereffects reflect a weighted function of retinal image shape and surface slant information, a hallmark of shape constancy operations. Our data establish that shape aftereffects are influenced perceived shape, as determined by constancy operations, and therefore likely involve higher-level neural substrates than previously thought.
Meeting abstract presented at VSS 2014