Baumann R, van der Zwan R, Peterhans E
Department of Neurology, University Hospital Zurich, Switzerland.
Eur J Neurosci. 1997 Jun;9(6):1290-303. doi: 10.1111/j.1460-9568.1997.tb01484.x.
An important task of vision is the segregation of figure and ground in situations of spatial occlusion. Psychophysical evidence suggests that the depth order at contours is defined early in visual processing. We have analysed this process in the visual cortex of the alert monkey. The animals were trained on a visual fixation task which reinforced foveal viewing. During periods of active visual fixation, we recorded the responses of single neurons in striate and prestriate cortex (areas V1, V2, and V3/V3A). The stimuli mimicked situations of spatial occlusion, usually a uniform light (or dark) rectangle overlaying a grating texture of opposite contrast. The direction of figure and ground at the borders of these rectangles was defined by the direction of the terminating grating lines (occlusion cues). Neuronal responses were analysed with respect to figure-ground direction and contrast polarity at such contours. Striate neurons often failed to respond to such stimuli, or were selective for contrast polarity; others were non-selective. Some neurons preferred a certain combination of figure-ground direction and contrast polarity. These neurons were rare both in striate and prestriate cortex. The majority of neurons signalled figure-ground direction independent of contrast polarity. These neurons were only found in prestriate cortex. We explain these responses in terms of a model which also explains neuronal signals of illusory contours. These results suggest that occlusion cues are used at an early level of processing to segregate figure and ground at contours.
视觉的一项重要任务是在空间遮挡的情况下分离图形和背景。心理物理学证据表明，轮廓处的深度顺序在视觉处理的早期就已确定。我们在警觉猴子的视觉皮层中分析了这一过程。对动物进行视觉注视任务训练，强化中央凹注视。在主动视觉注视期间，我们记录了纹状皮层和纹前皮层（V1、V2和V3/V3A区）单个神经元的反应。刺激模拟空间遮挡情况，通常是一个均匀的亮（或暗）矩形覆盖在具有相反对比度的光栅纹理上。这些矩形边界处图形和背景的方向由终止光栅线的方向（遮挡线索）确定。针对此类轮廓处的图形-背景方向和对比度极性分析神经元反应。纹状皮层神经元通常对此类刺激无反应，或对对比度极性具有选择性；其他神经元则无选择性。一些神经元偏好图形-背景方向和对比度极性的特定组合。这些神经元在纹状皮层和纹前皮层中都很罕见。大多数神经元发出的图形-背景方向信号与对比度极性无关。这些神经元仅在纹前皮层中发现。我们用一个模型来解释这些反应，该模型也解释了虚幻轮廓的神经元信号。这些结果表明，遮挡线索在处理的早期阶段被用于在轮廓处分离图形和背景。
