Carandini M, Ringach D L
Department of Neurobiology and Physicology, Northwestern University, Evanston, IL 60208, USA.
Vision Res. 1997 Nov;37(21):3061-71. doi: 10.1016/s0042-6989(97)00100-4.
Recurrent models of orientation selectivity in the visual cortex postulate that an initially broad tuning given by the pattern of geniculate afferents is substantially sharpened by intracortical feedback. We show that these models can be tested on the basis of their predicted responses to certain visual stimuli, without the need for pharmacological or physiological manipulations. First, we consider a detailed recurrent model proposed by Somers, Nelson and Sur [(1995) Journal of Neuroscience, 15, 5448-5465] and show that it can be simplified to a single equation: a center-surround feedback filter in the orientation domain. Then, we explore the responses of the simplified model to stimuli containing two or more orientations. We find that the model exhibits peculiar responses to stimuli containing two orientations, such as plaids or crosses: if the component orientations differ by less than 45 deg the model cannot distinguish between them; if the orientations differ by more than 45 deg the model overestimates their angle by as much as 30 deg. Moreover, the model cannot signal the presence of three orientations separated by 60 deg (it responds as if there were only two orientations), and the addition of two-dimensional visual noise to an oriented stimulus results in strong spurious responses at the orthogonal orientation. We argue that the effects of attraction and repulsion between orientations and the emergence of responses at off-optimal orientations are common to a wide class of feedback models of orientation selectivity. These models could thus be tested by measuring the visual responses of cortical neurons to stimuli containing multiple orientations.
视觉皮层中方向选择性的循环模型假定，由膝状传入神经模式给出的初始宽泛调谐通过皮层内反馈得到显著锐化。我们表明，这些模型可以根据其对某些视觉刺激的预测反应进行测试，而无需进行药理学或生理学操作。首先，我们考虑由萨默斯、尼尔森和苏尔提出的详细循环模型[（1995年）《神经科学杂志》，15，5448 - 5465]，并表明它可以简化为一个单一方程：方向域中的中心 - 外周反馈滤波器。然后，我们探索简化模型对包含两个或更多方向的刺激的反应。我们发现该模型对包含两个方向的刺激，如格子图案或十字图案，表现出奇特的反应：如果组成方向相差小于45度，模型无法区分它们；如果方向相差大于45度，模型会将它们的角度高估多达30度。此外，该模型无法识别由60度分隔的三个方向的存在（它的反应就好像只有两个方向），并且向定向刺激添加二维视觉噪声会在正交方向上产生强烈的虚假反应。我们认为方向之间的吸引和排斥效应以及非最佳方向上反应的出现是一大类方向选择性反馈模型所共有的。因此，可以通过测量皮层神经元对包含多个方向的刺激的视觉反应来测试这些模型。
