Retinotopic activity in V1 reflects the perceived and not the retinal size of an afterimage

An afterimage looks larger when one fixates on a distant than on a closer surface. We show that the retinotopic activity in the primary visual cortex (V1) associated with viewing an afterimage is modulated by perceived size, even when the size of the retinal image remains constant. This suggests that V1 has an important role in size constancy when the viewing distance of the stimulus changes.