Lee Gerick M, Majaj Najib J, Deliz C L Rodríguez, Kiorpes Lynne, Movshon J Anthony
Center for Neural Science, New York University, New York, NY, USA.
bioRxiv. 2025 Jan 4:2025.01.03.631258. doi: 10.1101/2025.01.03.631258.
Sensory stimuli vary across a variety of dimensions, like contrast, orientation, or texture. The brain must rely on population representations to disentangle changes in one dimension from changes in another. To understand how the visual system might extract separable stimulus representations, we recorded multiunit neuronal responses to texture images varying along two dimensions: contrast, a property represented as early as the retina, and naturalistic statistical structure, a property that modulates neuronal responses in V2 and V4, but not in V1. We measured how sites in these 3 cortical areas responded to variation in both dimensions. Contrast modulated responses in all areas. In V2 and V4, the presence of naturalistic structure both modulated responses and increased contrast sensitivity. Tuning for naturalistic structure was strongest in V4; tuning in both dimensions was most heterogeneous in V4. We measured how well populations in each area could support the linear readout of both dimensions. Populations in V2 and V4 could support the linear readout of naturalistic structure, but only in V4 did we find evidence for a robust representation that was contrast-invariant.
Single neurons in visual cortex respond selectively to multiple stimulus dimensions, so signals from single neurons cannot distinguish changes in one dimension from changes in another. We measured responses from simultaneously recorded neural populations in three hierarchically linked visual areas - V1, V2, and V4 - using texture stimuli that varied in two dimensions, contrast and naturalistic image structure. We used linear decoding methods to extract information about each dimension. In all three areas, contrast could be decoded independently of image structure. Only in V4, however, could image structure be decoded independently of contrast. The reason is that selectivity for texture and contrast in V4 was much more diverse than in V1 or V2. This heterogeneity allows V4 to faithfully represent naturalistic image structure independent of contrast.
感觉刺激在各种维度上有所不同，如对比度、方向或纹理。大脑必须依靠群体表征来区分一个维度的变化与另一个维度的变化。为了理解视觉系统如何提取可分离的刺激表征，我们记录了多单元神经元对沿两个维度变化的纹理图像的反应：对比度，一种早在视网膜就有表征的属性；以及自然统计结构，一种调节V2和V4区神经元反应，但不调节V1区神经元反应的属性。我们测量了这三个皮层区域的位点对两个维度变化的反应。对比度在所有区域都调节反应。在V2和V4区，自然结构的存在既调节反应又提高了对比度敏感性。对自然结构的调谐在V4区最强；两个维度的调谐在V4区最不均匀。我们测量了每个区域的群体能够在多大程度上支持两个维度的线性读出。V2和V4区的群体能够支持自然结构的线性读出，但只有在V4区我们才发现了对比度不变的稳健表征的证据。
视觉皮层中的单个神经元对多个刺激维度有选择性反应，因此单个神经元的信号无法区分一个维度的变化与另一个维度的变化。我们使用在对比度和自然图像结构两个维度上变化的纹理刺激，测量了三个层次相连的视觉区域——V1、V2和V4——中同时记录的神经群体的反应。我们使用线性解码方法来提取关于每个维度的信息。在所有三个区域，对比度都可以独立于图像结构进行解码。然而，只有在V4区，图像结构才能独立于对比度进行解码。原因是V4区对纹理和对比度的选择性比V1或V2区要多样化得多。这种异质性使得V4区能够独立于对比度忠实地表征自然图像结构。
