Human beings are capable of reaching toward and grasping objects in space with great precision, and vision plays an indispensable role in the control of this skilled behaviour. Not only does our arm extend toward the object, but our hand adjusts its shape in anticipation of the grasp itself. The long-term goal of research in my laboratory is to find out how the brain controls this complex behaviour and other visually guided movements of the limbs and body. With the use of a special recording system, we can reconstruct the movements of an individual's fingers, hand, arm, and eyes as he or she reaches out to pick up objects placed at different distances from the body. We then use a computer to analyze the form and timing of the movements. By comparing the performance of normal individuals and patients with damage to particular regions of the brain, we are gaining important insights into how information from the visual system and other sensory systems is used to control this important human behaviour. It is hoped that this research will help to answer one of the central questions in behavioural neuroscience -- how sensory inputs are transformed into useful motor acts.
My former postdoc, James Danckert, who now holds a Canada Research Chair at the University of Waterloo, worked with me on a project in which we showed that reaching movements made to targets in the lower visual field are more efficient than those made to targets in the upper visual field. This result is consistent with electrophysiological and anatomical studies showing a lower visual field bias in the central visual pathways - particularly in those pathways implicated in the control of skilled movements of the arm and hand.
More recently, David Westwood, another former postdoc in my lab (now a faculty member at Dalhouse University), showed that dedicated, real-time visuomotor mechanisms are engaged for the control of action only after a grasping movement is cued, and only if the target is visible. If the target object is not visible when the movement is cued, then grasping is driven, not by the dedicated visuomotor systems in the dorsal stream, but by information provided by the ventral perception stream.
Danckert, J., & Goodale, M.A. (2001). Superior performance for visually guided pointing in the lower visual field. Experimental Brain Research, 137, 303-308. Download pdf
Westwood, D.A., & Goodale, M.A. (2003). Perceptual illusion and the real-time control of action. Spatial Vision, 16, 243-254.
