Afterimages Reveal Interocular Transfer of Shape Adaptation

An afterimage's shape changes systematically depending on the adapted shape. Adapting to circles produces polygonal afterimages, whereas adapting to hexagons sometimes produce circular afterimages. In this study, a right-eye afterimage produced by adapting to circles was tested while the left eye adapted to a plain background, static circles, rotating circles, rotating stars, or rotating hexagons. Subjects rated the subjective roundness of the right-eye afterimage. Although the right eye adapted to circles, the ratings varied with the left-eye adaptation. After the left eye adapted to rotating hexagons, the right-eye afterimages were rated highest (most circular). In contrast, after the left eye adapted to rotating circles, the right-eye afterimages were rated lowest (most angular). This interocular transfer of shape adaptation demonstrates that afterimage shape is determined in a cortical area that collects information from both eyes