Nonlinear Processess at Intermediate Stages

描述（申请人提供）：大脑的大部分，可能是25-40%，专门用于视觉，但我们对它的了解很少。这里我们集中在视觉处理的中间阶段，低于对物体和场景的有意识感知，但高于视网膜逐点处理（大致是皮层区域V1到V4/MT）。人们普遍认为，在这个中间水平的一个重要过程是一组多通道或分析仪选择性敏感的方向，空间频率，空间位置，运动方向等，其生理基板可能是VIN 2的神经元。我们和其他人也提出了两种不同类型的非线性，作为中间级的重要过程：（i）空间非线性可能来自复杂的二阶通道，其中包含两级线性滤波，中间有整流。(ii)这里关注的强烈非线性依赖于视觉图案的对比度，并且在一般意义上作为对比度增益控制过程来操作。一个这样的过程是在正常化网络中起作用的皮质内抑制。其他可能性包括突触抑制、皮层区域内的易化或抑制性长距离相互作用以及从较高区域到较低区域的反馈。这一建议继续行为调查的两种非线性，因为它们在人类视觉感知的功能。一些进一步的工作提出了空间非线性，特别是复杂的通道的输出是否是概率独立的，并标记为他们去上游。然而，该建议集中于表征构成密集非线性的对比度增益控制过程。我们提出了一个新的线的心理物理调查这些过程的动态。这项调查建立在一个实验范式-时间探针正弦范式-已经证明了很大的用途，在表征视网膜光适应，亮度增益控制过程。探头正弦范式将在这里使用的心理物理研究纹理隔离和正弦波光栅掩蔽，研究旨在寻找不同的可能的对比度增益控制过程。可能的对比度增益控制过程的模型预测将用于指导解释的经验心理物理学的结果。了解这些动态可以帮助我们区分不同的过程，并了解它们的感知功能。

DESCRIPTION (provided by applicant): Much of the brain, perhaps 25-40% of it, is devoted to vision, and yet we understand little of it. Here we concentrate on the intermediate stages of visual processing that are lower than the conscious perception of objects and scenes but higher than retinal pointwise processing (roughly cortical areas V1 through V4/MT). There is widespread agreement that one important process at this intermediate level is a set of multiple channels or analyzers selectively sensitive to orientation, spatial frequency, spatial position, direction of motion, etc, the physiological substrate for which is probably the neurons of VIN2. Two different kinds of nonlinearity have also been proposed, by us and by others, as important processes at the intermediate level: (i) A spatial nonlinearity may result from complex second-order channels, which contain two stages of linear filtering with a rectification in between. (ii) The intensive nonlinearities of concern here depend on the visual pattern's contrast and operate in a general sense as contrast-gain-controlling processes. One such process is intracortical inhibition acting in a normalization network. Other possibilities include synaptic depression, facilitatory or inhibitory long-range interactions within a cortical area, and feedback from higher areas to lower areas. This proposal continues behavioral investigation of the two kinds of nonlinearity as they function in human visual perception. Some further work is proposed on the spatial nonlinearity, in particular on whether the complex channels' outputs are probabilistically independent and labeled as they go upstream. This proposal concentrates, however, on characterizing the contrast-gain-controlling processes that constitute the intensive nonlinearity. We propose a new line of psychophysical investigation into the dynamics of these processes. This investigation builds on an experimental paradigm -- the temporal Probe-Sine paradigm -- that has already proved of great use in characterizing retinal light adaptation, a luminance-gain-controlling process. The Probe-Sine paradigm will be used here in psychophysical studies of texture segregation and of sinewave-grating masking, studies designed to look at different possible contrast-gain-controlling processes. Predictions from models of possible contrast-gain-controlling processes will be used to guide interpretation of the empirical psychophysical results. Understanding the dynamics can help us both to distinguish among different processes and to understand their perceptual functions.