Patient P.A., who has a posterior callosotomy and right mediofrontal stroke, was assessed in his ability to recognize objects and their spatial location. When a set of pac-men was briefly displayed in the right visual field, P.A. was able to recognize both shape and location. In contrast, when stimuli were displayed in the left visual field, P.A. was unable to report object features either verbally or with his right hand. He couldn’t report whether two or four pac-men were being displayed, whether the pac-men were arranged to form an illusory square, and whether the pac-men were facing outward or inward. These data reveal an impaired callosal transfer of object information in P.A. In contrast, P.A. revealed unimpaired spatial abilities to left visual field stimuli. He was able to locate the cursor at the center of the display using his right hand, and to verbally report the pac-men’s location. We are currently exploring whether P.A.’s ability to localize objects that he cannot recognize is mediated by a covert orienting of attention to the object’s location.

This research was supported by a post-doctoral fellowship from the Rotman Research Institute and by a grant to the first author from the Heart and Stroke Foundation of Ontario.