US-German Collaboration: Circuit models of form processing in primate V4

本合作研究旨在结合电生理学、计算学、建模和心理物理学等方法，探讨视觉皮质V4区神经元新发现的特性对视觉物体识别的影响，V4区是大脑形状加工通路的重要中间阶段。V4神经元对各种形状属性有选择性地做出反应，但最近的研究表明，它们对刺激的对比度极性也有选择性，根据它们对相对于均匀背景的形状亮度对比度的偏好，可以大致分为四类。具体来说，等亮度细胞对完全由色彩对比定义的刺激反应最好，没有亮度对比，而明亮、黑暗和对比度细胞分别对正对比、负对比或两者中的任何一种反应最好。因为这些类别是基于简单的刺激，这些细胞如何对更自然的刺激做出反应仍然未知，其中边界很少由固定的亮度对比定义，以及不同的细胞类别是否在编码对象方面具有不同的功能角色。通过严格的心理物理测试开发的一套参数化的自然刺激来表征V4神经元，将为潜在的电路和功能提供新的见解，并打开对V4和腹侧流的新理解。大脑中视觉形式处理的计算模型也受到了限制：它们没有考虑到从视网膜到视觉皮层存在的现实生理细胞类型，它们主要针对处理消色差信号，并且严重依赖于前馈处理。这项研究将产生克服这些限制的模型，对于深入了解表单处理的电路和机制是非常宝贵的。这些模型将在一个开放的在线框架中提供，旨在为易用性和透明度设定一个标准，促进理论家和实验家之间的进一步合作，并促进教育。最后，在视觉科学中有一个长期存在的争论，这是由心理物理学文献引起的，它质疑颜色信号是否以及如何促进形式处理。传统观点认为，边界检测和分割仅仅是基于亮度对比。然后，颜色在确定的边界范围内绘制表面。最近的心理物理和理论研究与这一观点不一致，并认为颜色对自然场景的分割和形式处理很重要，例如，树叶中的水果，基于亮度对比的检测是非常困难的。本研究的实验将为这一争论提供急需的生理学数据，这里开发的模型将阐明皮层通路在多个阶段的功能组织，揭示我们自然视觉输入的不同方面如何有助于形成感知。该奖项由美国国家科学基金会国际科学与工程主任办公室共同资助。德国教育和研究部（BMBF）正在资助一个伙伴项目。

This collaborative study aims to advance the understanding of visual object recognition by combining electrophysiology, computational, modeling and psychophysics to probe the implications of newly discovered properties of neurons in visual cortical area V4, an important intermediate stage in the shape processing pathway of the brain.V4 neurons respond selectively to a variety of shape attributes, but recent studies demonstrate that they are also selective for the contrast polarity of stimuli and can be broadly classified into four categories based on their preference for the luminance contrast of shapes relative to a uniform background. Specifically, Equiluminance cells respond best to stimuli defined purely by a chromatic contrast with no luminance contrast while Bright, Dark and Contrast cells respond best to positive contrasts, negative contrasts or either, respectively. Because these categories are based on simple stimuli, it remains unknown how these cells respond to more naturalistic stimuli, where boundaries are seldom defined by a fixed luminance contrast, and whether the different cell classes have different functional roles for encoding objects. Characterizing V4 neurons with a parameterized set of naturalistic stimuli that are developed with rigorous psychophysical testing will provide novel insights into underlying circuitry and function and open new understanding about V4 and the ventral stream.Computational models of visual form processing in the brain have also been limited: they have not taken account of realistic physiological cell types known to exist from the retina to the visual cortex, they have been largely aimed at processing achromatic signals, and have relied heavily on feedfoward processing. This study will generate models that overcome these limitations and are invaluable for gaining insights into the circuits and mechanisms underlying form processing. These models will be available in an open, online framework designed to set a standard for ease of use and transparency, to spur further collaboration between theoreticians and experimentalists, and to facilitate education.Finally, there has been a longstanding debate in vision science, motivated from the psychophysical literature, that questions whether and how chromatic signals contribute to form processing. The traditional view has been that boundary detection and segmentation are solely based on luminance contrast. Color then paints a surface within the confines of the identified boundary. Recent psychophysical and theoretical studies are at odds with this view and argue that color is important for segmentation and form processing in natural scenes, for example, fruit amidst leaves, where detection based on luminance contrast is very difficult. The experiments in this study will inject much needed physiology data into this debate and the models developed here will shed light on the functional organization of cortical pathways at multiple stages, revealing how different aspects of our natural visual input contribute to form perception.This award is being co-funded by NSF's Office of the Director, International Science and Engineering. A companion project is being funded by the German Ministry of Education and Research (BMBF).