The Visual Control of Grasping

人类的手是一件了不起的工程学作品。我们可以精准地伸手抓住物体--远远好于目前研发出的任何机器人。使这成为可能的一件事是我们敏锐的视觉。梅尔·古代尔教授和他在韦斯特大脑与心灵研究所的同事们正在研究视觉信息如何在手伸出手并抓住物体时用于引导它，以前使用工具等物体的经验如何影响抓住物体的方式，与我们互动的其他人的存在如何影响我们的抓住，以及大脑的哪些区域参与了这些不同的情况。为了研究手是如何移动的，古代尔教授使用特殊的红外线敏感相机来跟踪安装在指尖、手和手腕上的微小红外光。然后，这些摄像头的数据可以用来重建抓取运动展开时手和手指的轨迹。 古代尔教授实验室之前的工作表明，来自两只眼睛的信息--双目视觉--在引导这些动作方面发挥着重要作用。但也有其他信息来源，包括我们四处走动时眼睛上世界的运动，以及一大堆被称为“深度的图片线索”的线索。这些后一种线索--透视、熟悉的大小、遮挡、阴影和纹理渐变--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。古代尔博士和他的团队正在探索所有这些不同的线索在计划和控制手的抓握动作中所起的作用，以及这些线索如何与之前对世界的经验和知识相互作用。他特别感兴趣的是尺寸的恒定性，即手对目标对象的张开量是相同的，而不是它与身体的实际距离。他希望探索对“握力恒定”至关重要的距离线索，以及这些线索是否与感知的大小恒定有关。他还研究了我们如何处理大小的视觉错觉--并且已经证明，欺骗我们眼睛的错觉很少能愚弄我们的抓手！最近，古代尔博士开始使用脑成像技术(功能磁共振成像和脑电成像)来探索大脑如何计算出我们试图抓住的物体的大小，并在我们拿起工具时选择合适的手势。最后，他的团队正在研究当我们抓住物体以便将其递给他人或向他人展示如何拿起物体时，我们动作中的细微差别。这项工作不仅提供了关于如何使用视觉来控制人类手的基本信息，而且还有助于设计更好的控制机器人手的系统，以及更有效和更透明的人机界面。这将不是生物学第一次为工程学提供一些设计方面的有用课程。

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.