Ziemba Corey M, Freeman Jeremy, Simoncelli Eero P, Movshon J Anthony
Center for Neural Science, New York University , New York, New York.
Howard Hughes Medical Institute, New York University , New York, New York.
J Neurophysiol. 2018 Aug 1;120(2):409-420. doi: 10.1152/jn.00900.2017. Epub 2018 Apr 11.
The stimulus selectivity of neurons in V1 is well known, as is the finding that their responses can be affected by visual input to areas outside of the classical receptive field. Less well understood are the ways selectivity is modified as signals propagate to visual areas beyond V1, such as V2. We recently proposed a role for V2 neurons in representing the higher order statistical dependencies found in images of naturally occurring visual texture. V2 neurons, but not V1 neurons, respond more vigorously to "naturalistic" images that contain these dependencies than to "noise" images that lack them. In this work, we examine the dependency of these effects on stimulus size. For most V2 neurons, the preference for naturalistic over noise stimuli was modest when presented in small patches and gradually strengthened with increasing size, suggesting that the mechanisms responsible for this enhanced sensitivity operate over regions of the visual field that are larger than the classical receptive field. Indeed, we found that surround suppression was stronger for noise than for naturalistic stimuli and that the preference for large naturalistic stimuli developed over a delayed time course consistent with lateral or feedback connections. These findings are compatible with a spatially broad facilitatory mechanism that is absent in V1 and suggest that a distinct role for the receptive field surround emerges in V2 along with sensitivity for more complex image structure. NEW & NOTEWORTHY The responses of neurons in visual cortex are often affected by visual input delivered to regions of the visual field outside of the conventionally defined receptive field, but the significance of such contextual modulations are not well understood outside of area V1. We studied the importance of regions beyond the receptive field in establishing a novel form of selectivity for the statistical dependencies contained in natural visual textures that first emerges in area V2.
V1区神经元的刺激选择性是众所周知的，同样已知的是，它们的反应会受到经典感受野之外区域的视觉输入的影响。而对于信号传播到V1区之外的视觉区域（如V2区）时选择性如何被改变，人们了解得较少。我们最近提出，V2区神经元在表征自然视觉纹理图像中发现的高阶统计依赖性方面发挥作用。V2区神经元，而非V1区神经元，对包含这些依赖性的“自然主义”图像的反应比对缺乏这些依赖性的“噪声”图像的反应更强烈。在这项研究中，我们研究了这些效应对刺激大小的依赖性。对于大多数V2区神经元来说，当以小斑块形式呈现时，对自然主义刺激而非噪声刺激的偏好较为适度，且随着大小增加而逐渐增强，这表明负责这种增强敏感性的机制在比经典感受野更大的视野区域上起作用。事实上，我们发现噪声的周围抑制比自然主义刺激更强，并且对大的自然主义刺激的偏好是在与侧向或反馈连接一致的延迟时间过程中形成的。这些发现与V1区不存在的空间广泛促进机制相一致，并表明V2区感受野周围出现了独特作用，同时伴随着对更复杂图像结构的敏感性。新发现与值得关注之处视觉皮层神经元的反应通常会受到传递到传统定义感受野之外视野区域的视觉输入的影响，但除V1区外，这种背景调制的意义尚未得到很好的理解。我们研究了感受野之外区域在建立对自然视觉纹理中包含的统计依赖性的新型选择性方面的重要性，这种选择性首先出现在V2区。
