De Valois R L, Cottaris N P
Psychology Department, University of California, Berkeley, CA 94720, USA.
Proc Natl Acad Sci U S A. 1998 Nov 24;95(24):14488-93. doi: 10.1073/pnas.95.24.14488.
It is clear that the initial analysis of visual motion takes place in the striate cortex, where directionally selective cells are found that respond to local motion in one direction but not in the opposite direction. Widely accepted motion models postulate as inputs to directional units two or more cells whose spatio-temporal receptive fields (RFs) are approximately 90 degrees out of phase (quadrature) in space and in time. Simple cells in macaque striate cortex differ in their spatial phases, but evidence is lacking for the varying time delays required for two inputs to be in temporal quadrature. We examined the space-time RF structure of cells in macaque striate cortex and found two subpopulations of (nondirectional) simple cells, some that show strongly biphasic temporal responses, and others that are weakly biphasic if at all. The temporal impulse responses of these two classes of cells are very close to 90 degrees apart, with the strongly biphasic cells having a shorter latency than the weakly biphasic cells. A principal component analysis of the spatio-temporal RFs of directionally selective simple cells shows that their RFs could be produced by a linear combination of two components; these two components correspond closely in their respective latencies and biphasic characters to those of strongly biphasic and weakly biphasic nondirectional simple cells, respectively. This finding suggests that the motion system might acquire the requisite temporal quadrature by combining inputs from these two classes of nondirectional cells (or from their respective lateral geniculate inputs, which appear to be from magno and parvo lateral geniculate cells, respectively).
很明显，视觉运动的初始分析发生在纹状皮层，在那里发现了方向选择性细胞，它们对一个方向的局部运动有反应，而对相反方向的运动没有反应。被广泛接受的运动模型假定，作为方向单元输入的是两个或更多细胞，其时空感受野（RFs）在空间和时间上大约相差90度（正交）。猕猴纹状皮层中的简单细胞在空间相位上有所不同，但缺乏证据表明两个输入要达到时间正交所需的不同时间延迟。我们研究了猕猴纹状皮层中细胞的时空RF结构，发现了（非定向）简单细胞的两个亚群，一些细胞表现出强烈的双相时间反应，而另一些细胞即使有也是微弱的双相反应。这两类细胞的时间脉冲反应非常接近90度，强烈双相的细胞比微弱双相的细胞潜伏期更短。对方向选择性简单细胞的时空RFs进行主成分分析表明，它们的RFs可以由两个成分的线性组合产生；这两个成分在各自的潜伏期和双相特征上分别与强烈双相和微弱双相的非定向简单细胞的潜伏期和双相特征密切对应。这一发现表明，运动系统可能通过组合来自这两类非定向细胞（或来自它们各自的外侧膝状体输入，分别似乎来自大细胞和小细胞外侧膝状体细胞）的输入来获得所需的时间正交。
