Topographic representation of an occluded object and the effects of spatiotemporal context in human early visual areas.

Abstract

Occlusion is a primary challenge facing the visual system in perceiving object shapes in intricate natural scenes. Although behavior, neurophysiological, and modeling studies have shown that occluded portions of objects may be completed at the early stage of visual processing, we have little knowledge on how and where in the human brain the completion is realized. Here, we provide functional magnetic resonance imaging (fMRI) evidence that the occluded portion of an object is indeed represented topographically in human V1 and V2. Specifically, we find the topographic cortical responses corresponding to the invisible object rotation in V1 and V2. Furthermore, by investigating neural responses for the occluded target rotation within precisely defined cortical subregions, we could dissociate the topographic neural representation of the occluded portion from other types of neural processing such as object edge processing. We further demonstrate that the early topographic representation in V1 can be modulated by prior knowledge of a whole appearance of an object obtained before partial occlusion. These findings suggest that primary "visual" area V1 has the ability to process not only visible or virtually (illusorily) perceived objects but also "invisible" portions of objects without concurrent visual sensation such as luminance enhancement to these portions. The results also suggest that low-level image features and higher preceding cognitive context are integrated into a unified topographic representation of occluded portion in early areas.