CRCNS Research Proposal: Computations for spatial-chromatic interactions and their physiological implementation in primary visual cortex

颜色和形式通常被视为图像的可分离特征。人们可以在非彩色照片中识别形状，并从形状中抽象出物体的颜色。然而，从视觉通路的第一阶段开始，特定颜色的处理嵌入整个视觉通路，在那里，对视觉光谱不同部分敏感的三种不同类型的光传感器(锥体)最初将光转换为电脉冲。原则上，给定点的颜色可以通过比较三种不同锥体类型的激活来确定，但单独的颜色通道一直保持到初级视觉皮质(V1)，在那里它们最终组合在同时对不同空间模式敏感的神经元中。事实上，虽然最初认为颜色和形状在V1内是通过不同的路径处理的，但最近的实验强调，令人惊讶的是，V1神经元以不同的方式将它们混合在一起。这种混合究竟是如何发生的，以及为了什么目的，是理解人类视觉的关键开放问题，而且一直很难回答，因为这种混合太复杂了，无法用传统方法来描述。该项目将V1神经活动的大规模记录与新的计算方法相结合，提供了对V1内颜色处理的史无前例的高分辨率描述，同时允许确定空间-颜色混合在支持自然颜色视觉方面的潜在功能。该项目还为本科生和研究生提供了神经生理学和基于机器学习的统计建模的跨学科培训机会。该项目是视觉神经生理学、数据驱动的计算建模和模拟的紧密结合。研究人员在皮质板层上进行大规模多电极记录，以确定从皮质输入(其中颜色通道是分开的)到皮质输出(其中它们是混合的)的空间-色度表示的转换。这些记录使用非线性数据驱动模型进行解释，该模型可以提供驱动每个V1神经元的刺激的高分辨率空间色度图，并区分每个阶段执行的基本计算。通过利用新的基于模型的眼球跟踪来推动这种特征以实现锥体分辨率，该眼球跟踪可以解释微小的眼球运动，具有比标准方法更精细的数量级的灵敏度。第一个目标决定了在V1中如何组合空间和色度信息的一套原则，这为整个视觉通路的处理奠定了基础。第二个目的是确定这些规则在处理凝视中心(中心凹)的皮质区域是否相同，该区域负责高敏锐度的颜色视觉。最后，最后一个目标建立了一个群体解码框架，用于将单个V1细胞的空间-色度敏感度与处理自然颜色视觉的更大系统范围的视觉皮质目标联系起来。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Color and form are often treated as separable features of an image. One can recognize shapes in achromatic photographs and conceptualize the color of an object abstracted from shape. Yet color-specific processing is embedded throughout the visual pathway from the first stage of the visual pathway, where three different types of light sensors (“cones”) with sensitivity to different parts of the visual spectrum initially convert light into electrical impulses. The color of a given point can in principle be determined by comparing the activation of the three different cone types, but the separate color channels are maintained until the primary visual cortex (V1), where they are finally combined in neurons that concurrently have sensitivity to different spatial patterns. Indeed, while it was initially thought that color and form were processed through separate pathways within V1, recent experiments have highlighted that a surprising fraction of V1 neurons mix them together in a diversity of ways. Exactly how the mixing occurs, and for what purpose, are critical open questions in understanding human vision, and have been difficult to answer because such mixing is too complicated to characterize using traditional approaches. This project combines large-scale recording of V1 neural activity during tailored “spatio-chromatic” visual stimulation with new computational approaches that offer an unprecedented high-resolution description of color processing within V1 while allowing determination of the underlying function of spatio-chromatic mixing in supporting natural color vision. The project also provides opportunity for cross-disciplinary training in neurophysiological and machine-learning based statistical modeling of undergraduate and graduate students.This project is a tight combination of visual neurophysiology, data-driven computational modeling, and simulation. The investigators perform large-scale multi-electrode recordings across cortical lamina to determine the transformations of spatio-chromatic representations from cortical inputs (where color channels are separate) to cortical outputs (where they are mixed). These recordings are interpreted using nonlinear data-driven models that can provide high-resolution spatio-chromatic maps of the stimuli driving each V1 neuron, and distinguish the underlying computations being performed at each stage. Such characterizations are pushed to achieve cone-resolution by leveraging novel model-based eye-tracking that can account for small eye movements with an order-of-magnitude finer sensitivity than standard approaches. The first Aim determines the set of principles governing how spatial and chromatic information is combined in V1, which sets the foundation for processing throughout the visual pathway. The second Aim determines whether these rules are the same in the area of cortex processing the center-of-gaze (fovea), which is responsible for high-acuity color vision. Finally, the last Aim establishes a population decoding framework for linking spatio-chromatic sensitivity of individual V1 cells to the larger systems-wide goals of the visual cortex in processing natural color vision.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.