The Visual Control of Grasping

人类的手是一项非凡的工程。我们可以伸出手，精确地抓住物体——比目前开发的任何机器人都要好得多。使这一切成为可能的原因之一是我们敏锐的视觉。韦斯特大学大脑与心理研究所的梅尔·古德尔教授和他的同事们正在研究视觉信息是如何被用来指导手伸出并抓住一个物体的，以前接触物体（如工具）的经验是如何影响手抓住一个物体的，与我们互动的其他人的存在是如何影响我们的抓住的，以及在这些不同的情况下，大脑的哪些区域参与其中。为了研究手是如何运动的，古德尔教授使用特殊的红外敏感摄像机来跟踪附着在指尖、手和手腕上的微小红外光。然后，这些相机的数据可以用来重建手和手指在抓取运动展开时的轨迹。

The human hand is a remarkable piece of engineering. We can reach out and grasp objects with exquisite accuracy - far better than any robot yet developed. One of the things that makes this possible is our keen sense of sight. Prof. Mel Goodale and his colleagues at Western's Brain and Mind Institute are studying how visual information is used in guiding the hand as it reaches out and grasps an object, how previous experience with objects such as tools affects how an object is grasped, how the presence of others with whom we are interacting affects our grasping, and what brain areas are engaged in these different situations. To study how the hand is moving, Prof. 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 Prof. Goodale's lab has shown that information from the two eyes - binocular vision - plays 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 particularly interested in size constancy, the fact that the hand opens the same amount for a goal object independent of its actual distance from the body. He hopes to explore the distance cues that are critical for this 'grip constancy' and whether or not these cues are shared with perceptual size constancy'. He is also looking at how we cope with visual illusions of size - 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, and electroencephalography, or EEG) to explore how the brain computes the size of objects that we are trying to grasp and selects the appropriate hand posture when we pick up a tool. Finally, his team is study the subtle differences in the movements we make when we grasp objects in order to hand them to others or to show others how to pick up an object. 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 and for more efficient and transparent human-machine interfaces. This would not be the first time that biology has provided engineering with some useful lessons in design.