Preferential responses to occluded objects in the human visual cortex.

How do we see an object when it is partially obstructed from view? The neural mechanisms of this intriguing process are unclear, in part because studies of visual object perception heretofore have largely used stimuli of individual objects, such as faces or common inanimate objects, each presented alone. But in natural images, visual objects are typically occluded by other objects. Computational studies indicate that the perception of an occluded object requires processes that are substantially different from those for an unoccluded object in plain view. We studied the neural substrates of the perception of occluded objects using functional magnetic resonance imaging (fMRI) of human subjects viewing stimuli that were designed to elicit or not elicit the percept of an occluded object but were physically very similar. We hypothesized the regions that are selective for occluded objects, if they exist, will be differentially active during the two conditions. We found two regions, one in the ventral object processing pathway and another in the dorsal object processing pathway, that were significantly responsive to occluded objects. More importantly, both regions were significantly more responsive to occluded objects than to unoccluded objects, and this enhanced response was not attributable to low-level differences in the stimuli, amodal completion per se, or the behavioral task. Our results identify regions in the visual cortex that are preferentially responsive to occluded objects relative to other stimuli tested and indicate that these regions are likely to play an important role in the perception of occluded objects.