The Visual Control of Grasping

人类的手是一项了不起的工程。我们可以伸出手来，以极高的准确度抓住物体--比迄今为止开发的任何机器人都要好。使这成为可能的因素之一是我们敏锐的视觉。Mel Goodale教授和他的同事们正在研究视觉信息如何用于指导手伸出手并抓住物体，以前对工具等物体的经验如何影响物体的抓握方式，我们与之互动的其他人的存在如何影响我们的抓握，以及在这些不同的情况下大脑区域的参与。为了研究手是如何移动的，古德尔教授使用特殊的红外敏感相机来跟踪附着在指尖、手和手腕上的微小红外光。然后，这些摄像机的数据可以用来重建手和手指在抓握运动展开时的轨迹。Goodale教授实验室以前的工作表明，来自两只眼睛的信息-双眼视觉-在指导这些运动中起着重要作用。但也有其他的信息来源，包括当我们四处走动时，我们眼中的世界的运动和一系列被称为“深度图像线索”的线索。后一种线索--透视、熟悉的大小、遮挡、阴影和纹理梯度--几个世纪以来一直被艺术家们用来在二维画布上描绘三维世界。古德尔博士和他的团队正在探索所有这些不同的线索在规划和控制手部抓握动作中的作用，以及这些线索如何与先前的经验和对世界的知识相互作用。他对大小恒定性特别感兴趣，即手对目标物体的张开量与其与身体的实际距离无关。他希望探索对这种“抓握恒定性”至关重要的距离线索，以及这些线索是否与感知大小恒定性共享。 他还研究了我们如何科普大小的视觉错觉--并且已经表明，欺骗我们眼睛的错觉很少能欺骗我们抓握的手！最近，古德尔博士开始使用大脑成像（功能性磁共振成像，或fMRI，和脑电图，或EEG）来探索大脑如何计算我们试图抓住的物体的大小，以及当我们拿起工具时选择合适的手姿势。最后，他的团队正在研究当我们抓住物体以将其交给他人或向他人展示如何拿起物体时，我们所做动作的细微差异。这项工作不仅提供了有关如何使用视觉控制人手的基本信息，而且还有助于设计更好的系统来控制机器人手，以及更有效和透明的人机界面。这不是生物学第一次为工程学提供设计方面的有用经验。

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.