Identifying objects seen from different viewpoints. A PET investigation.

Positron emission tomography scans were acquired when subjects performed three tasks, each in a separate block of trials. They decided whether words named pictures of objects viewed from a canonical perspective, decided whether words named pictures of objects viewed from a non-canonical (unusual) perspective or saw random patterns of lines and pressed a pedal when they heard the word (this was a baseline condition). The dorsolateral prefrontal region was activated when subjects identified objects seen from non-canonical perspectives, as expected if the frontal lobes are involved in top-down perceptual processing. In addition, several areas in the occipital, temporal and parietal lobes were selectively activated when subjects identified objects seen from non-canonical perspectives, as specifically predicted by a recent theory. Overall, the pattern of results supported the view that the human brain identifies objects by using a system of areas similar to that suggested by studies of other primates.