von der Heydt R, Peterhans E
Department of Neurology, University Hospital Zurich, Switzerland.
J Neurosci. 1989 May;9(5):1731-48. doi: 10.1523/JNEUROSCI.09-05-01731.1989.
We have studied the mechanism of contour perception by recording from neurons in the visual cortex of alert rhesus monkeys. In order to assess the relationship between neural signals and perception, we compared the responses to edges and lines with the responses to patterns in which human observers perceive a contour where no line or edge is given (anomalous contour), such as the border between gratings of thin lines offset by half a cycle. With only one exception out of 60, orientation-selective neurons in area V1 did not signal the anomalous contour. Many neurons failed to respond to this stimulus at all, others responded according to the orientation of the grating lines. In area V2, 45 of 103 neurons (44%) signaled the orientation of the anomalous contour. Sixteen did so without signaling the orientation of the inducing lines. Some responded better to anomalous contours than to the optimum bars or edges. Preferred orientations and widths of tuning for anomalous contour and bar or edge were found to be highly correlated, but not identical, in each neuron. Similar to perception, the neuronal responses depended on a minimum number of lines inducing the contour, but not so much on line spacing, and tended to be weaker when the lines were oblique rather than orthogonal to the border. With oblique lines, the orientations signaled were biased towards the orientation orthogonal to the lines, as in the Zöllner illusion. We conclude that contours may be defined first at the level of V2. While the unresponsiveness of neurons in V1 to this type of anomalous contour is in agreement with linear filter predictions, the responses of V2 neurons need to be explained. We assume that they sum the signals of 2 parallel paths, one that defines edges and lines and another that defines anomalous contours by pooling signals from end-stopped receptive fields oriented mainly orthogonal to the contour.
我们通过记录警觉的恒河猴视觉皮层中的神经元，研究了轮廓感知的机制。为了评估神经信号与感知之间的关系，我们将对边缘和线条的反应与对那些人类观察者能感知到轮廓但实际上没有线条或边缘的图案（异常轮廓）的反应进行了比较，比如由细线光栅错开半个周期形成的边界。在V1区域，60个方向选择性神经元中只有一个例外，它们没有对异常轮廓发出信号。许多神经元对这种刺激根本没有反应，其他神经元则根据光栅线的方向做出反应。在V2区域，103个神经元中有45个（44%）对异常轮廓的方向发出了信号。其中16个在没有对诱导线条的方向发出信号的情况下做到了这一点。一些神经元对异常轮廓的反应比对最佳条形或边缘的反应更好。在每个神经元中，发现异常轮廓以及条形或边缘的偏好方向和调谐宽度高度相关，但并不完全相同。与感知类似，神经元的反应取决于诱导轮廓的线条的最小数量，但对线间距的依赖程度较小，并且当线条是倾斜的而非与边界正交时，反应往往较弱。对于倾斜的线条，发出信号的方向偏向于与线条正交的方向，就像在佐尔纳错觉中那样。我们得出结论，轮廓可能首先在V2水平被定义。虽然V1区域的神经元对这种类型的异常轮廓无反应与线性滤波器的预测一致，但V2神经元的反应需要得到解释。我们假设它们对两条平行路径的信号进行求和，一条路径定义边缘和线条，另一条路径通过汇集主要与轮廓正交的终端停止感受野的信号来定义异常轮廓。
