Grant: Doctoral Award - Frederick Banting and Charles Best Canada Graduate Scholarships

In our everyday movements, we typically interact directly with the object that we are viewing. Hence, the visual stimulus guiding the action is itself the target of the action. Such behaviour can be considered "standard", or "direct". However, the evolution of the capacity for tool-use in primates has resulted in situations where the correspondence between vision and action is not direct. Rather, the mapping between stimulus and response must be learned and calibrated. This situation has been referred to as "non-standard" sensorimotor mapping. In non-standard visually-guided reaching, the visual information used to perform a motor task does not come from the object one's hand is interacting with. A common example is a reach for a peripherally-viewed computer mouse sitting on a flat tabletop while viewing an icon on a computer monitor, and then sliding the mouse forward on a horizontal plane in order to displace a cursor vertically to touch the icon. In this situation, the direction of gaze and the manipulated object (the cursor) are in different depths or spatial planes. Our previous work has begun to characterize the contributions of different brain pathways to the processing of different levels of visuomotor compatibility. In this first study we test the hypothesis that neural pathways involving the superior parietal lobule are involved in basic visuomotor transformations and in decoupling the movements of the eyes and the hand, a skill required for some non-standard mapping tasks. We will be examining the performance of three optic ataxic patients in reaching tasks which involve different levels of dissociation (spatial plane changes, rotated visual feedback, and arbitrary associations). We will observe whether the damaged superior parietal lobule in the patients is necessary for other levels of dissociation in addition to performing reaches that involve a 180 degree rotation of the feedback compared with the motor output.