Pack C C, Born R T
Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115, USA.
Nature. 2001 Feb 22;409(6823):1040-2. doi: 10.1038/35059085.
A critical step in the interpretation of the visual world is the integration of the various local motion signals generated by moving objects. This process is complicated by the fact that local velocity measurements can differ depending on contour orientation and spatial position. Specifically, any local motion detector can measure only the component of motion perpendicular to a contour that extends beyond its field of view. This "aperture problem" is particularly relevant to direction-selective neurons early in the visual pathways, where small receptive fields permit only a limited view of a moving object. Here we show that neurons in the middle temporal visual area (known as MT or V5) of the macaque brain reveal a dynamic solution to the aperture problem. MT neurons initially respond primarily to the component of motion perpendicular to a contour's orientation, but over a period of approximately 60 ms the responses gradually shift to encode the true stimulus direction, regardless of orientation. We also report a behavioural correlate of these neural responses: the initial velocity of pursuit eye movements deviates in a direction perpendicular to local contour orientation, suggesting that the earliest neural responses influence the oculomotor response.
解读视觉世界的关键一步是整合移动物体产生的各种局部运动信号。这一过程因局部速度测量会因轮廓方向和空间位置的不同而变得复杂。具体而言，任何局部运动探测器只能测量垂直于延伸至其视野之外的轮廓的运动分量。这种“孔径问题”与视觉通路早期的方向选择性神经元尤为相关，在这些区域，小的感受野仅允许对移动物体有有限的视野。在这里，我们表明猕猴大脑颞中区（称为MT或V5）的神经元揭示了一种解决孔径问题的动态方法。MT神经元最初主要对垂直于轮廓方向的运动分量做出反应，但在大约60毫秒的时间内，反应逐渐转变为编码真实的刺激方向，而与方向无关。我们还报告了这些神经反应的行为关联：追踪眼球运动的初始速度在垂直于局部轮廓方向的方向上发生偏差，这表明最早的神经反应会影响动眼反应。
