The Visual Control of Grasping

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The human hand is a remarkable piece of engineering. As humans, we can reach out and grasp objects with exquisite accuracy - far better than any robot. One of the things that makes this possible is our keen sense of sight. Dr. Mel Goodale and his colleagues at the Centre for Brain and Mind at the University of Western Ontario are studying the different kinds of information that our visual system uses to guide the hand as it reaches out and grasps an object - and how previous experience with the object interacts with current visual information. To study how the hand is moving, Dr. Goodale uses special infra-red sensitive cameras to track tiny infra-red lights that have been attached to the fingertips, hand, and wrist. The data from these cameras can then be used to reconstruct the trajectory of the hand and fingers as the grasping movement unfolds. Previous work in Dr. Goodale's lab has shown that information from the two eyes - binocular vision - play an important role in the guidance of these movements. But there are other sources of information as well, including the motion of the world on our eyes as we move around and a whole host of cues called 'pictorial cues to depth'. These latter cues - perspective, familiar size, occlusion, shadows, and texture gradients - have been exploited by artists for centuries to depict a three-dimensional world on a two-dimensional canvas. Dr. Goodale and his team are exploring the role of all these different cues in the planning and control of grasping movements of the hand - and how these cues interact with previous experience and knowledge about the world. He is also looking at how we cope with visual illusions - and has already shown that illusions that deceive our eyes rarely fool our grasping hand! Recently, Dr. Goodale has begun to use brain imaging (functional magnetic resonance imaging, or fMRI) to explore how the brain computes the size of objects that we are trying to grasp. This work is not only providing basic information about how vision is used to control the human hand but is also helping in the design of better systems for controlling robot hands. This is not the first time that biology has provided engineering with some useful lessons in design.