Nonlinear Processess at Intermediate Stages

描述(申请人提供)：大脑的大部分，可能有25%-40%，致力于视觉，但我们对它知之甚少。在这里，我们集中在视觉加工的中间阶段，低于对物体和场景的有意识感知，但高于视网膜点状加工(大致是皮质区V1到V4/MT)。人们普遍认为，在这一中间水平上的一个重要过程是一组对方位、空间频率、空间位置、运动方向等选择性敏感的多通道或分析器，其生理底物可能是VIN2神经元。我们和其他人也提出了两种不同类型的非线性，作为中间水平的重要过程：(I)空间非线性可能是由复杂的二阶通道引起的，其中包含两级线性滤波和中间的校正。(Ii)这里所关注的强烈的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运行。一个这样的过程是作用于归一化网络的皮质内抑制。其他可能包括突触抑制，促进或抑制皮质区域内的远程相互作用，以及从较高区域到较低区域的反馈。这一建议继续对这两种非线性在人类视觉感知中的作用进行行为学研究。对空间非线性提出了进一步的工作，特别是关于复杂通道的输出是否在上行时是概率独立的和标记的。然而，这一建议集中在表征构成强烈非线性的对比度增益控制过程。我们提出了一条新的心理物理研究路线来研究这些过程的动力学。这项研究建立在一个实验范式--时间探测-正弦范式--已经被证明在表征视网膜光适应方面非常有用，这是一种亮度增益控制过程。Probe-Sine范式将在这里用于纹理分离和正弦波-光栅掩模的心理物理研究，这两个研究旨在观察不同可能的对比度增益控制过程。来自可能的对比度增益控制过程模型的预测将被用于指导对经验心理物理结果的解释。理解动力学可以帮助我们区分不同的过程，并理解它们的知觉功能。

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.