Wall Matthew B, Smith Andrew T
Department of Psychology, Royal Holloway, University of London, Egham, TW20 0EX, United Kingdom.
Curr Biol. 2008 Feb 12;18(3):191-4. doi: 10.1016/j.cub.2007.12.053. Epub 2008 Jan 24.
An essential function of visual processing is to establish the position of the body in space and, in concert with the other sense systems, to monitor movement of the whole body, or "egomotion." A key cue to egomotion is optic flow. For example, forward motion through the environment generates an expanding pattern of flow on the retina, and (with eyes fixed centrally) the direction of heading corresponds to the center of expansion [1]. In macaques, visual cortical area MST is sensitive to optic-flow structure [2, 3], and it has been suggested that MST has a central role in the computation of heading [4]. However, here we identify two areas of the human brain that represent visual cues to egomotion more directly than does MST. These areas respond strongly to a single optic-flow stimulus but become relatively unresponsive when the stimulus is surrounded with further flow patches and thereby made inconsistent with egomotion. One is putative area VIP in the anterior portion of the intraparietal sulcus. The other is a new visual area, which we refer to as cingulate sulcus visual area (CSv). Areas V1-V4 and MT respond about equally to both types of flow stimulus. MST has intermediate properties, responding well to multiple patches but with a modest preference for a single, egomotion-compatible patch. We suggest that MST is merely an intermediate processing stage for visual cues to egomotion and that such cues are more comprehensively encoded by VIP and CSv.
视觉处理的一个基本功能是确定身体在空间中的位置，并与其他感觉系统协同监测整个身体的运动，即“自我运动”。自我运动的一个关键线索是光流。例如，在环境中向前运动会在视网膜上产生一种扩展的流模式，并且（当眼睛固定在中央时）前进方向对应于扩展中心[1]。在猕猴中，视觉皮层区域MST对光流结构敏感[2,3]，并且有人认为MST在前进方向的计算中起核心作用[4]。然而，在这里我们确定了人类大脑中的两个区域，它们比MST更直接地代表自我运动的视觉线索。这些区域对单个光流刺激有强烈反应，但当刺激被更多的流斑块包围从而与自我运动不一致时，它们的反应就会相对减弱。一个是顶内沟前部的假定区域VIP。另一个是一个新的视觉区域，我们称之为扣带沟视觉区域（CSv）。V1-V4区域和MT区域对两种类型的流刺激的反应大致相同。MST具有中等特性，对多个斑块反应良好，但对单个与自我运动兼容的斑块有适度偏好。我们认为MST仅仅是自我运动视觉线索的一个中间处理阶段，并且这些线索由VIP和CSv更全面地编码。
