The statistical computation underlying contrast gain control
The statistical computation underlying contrast gain control
复制标题
DOI：
10.1523/jneurosci.0284-06.2006
复制
发表时间：
2006-06-07
影响因子：
5.3
通讯作者：
Carandini, Matteo
中科院分区：
文献类型：
--
作者：
Bonin, Vincent;Mante, Valerio;Carandini, Matteo
在早期的视觉系统中，对比度增益控制机制基于局部流行的对比度来设置响应的增益。这种适应机制使用的对比度度量通常被假定为光强度相对于平均值(均方根对比度)的标准偏差。然而，有许多替代方案是可能的。例如，对比度的测量可能取决于相对于平均值的绝对偏差，或者取决于最暗或最亮强度的普遍程度。我们研究了猫的外侧膝状核中这种对比度测量背后的统计计算，它将信号从视网膜传递到皮质。借用心理物理学的方法，我们记录了白噪声刺激的反应，其强度分布是精确变化的。我们改变了亮度分布的标准差、偏度和峰度，同时保持平均亮度不变。我们发现，增益强烈地依赖于分布的标准差。此外，在恒定的标准差下，增益不随偏度或峰度的变化而变化。这些发现对ON和OFF细胞都适用，表明对比度的测量与细胞发出的刺激强度范围无关。这些结果证实了长期以来的假设，即对比度增益控制计算均方根对比度。它们还表明，对比度增益控制可以感知强度的全部分布，并保持不同细胞类型的相对反应不变。这种非常特殊的计算在视觉处理方面的优势并不完全为人所知。
In the early visual system, a contrast gain control mechanism sets the gain of responses based on the locally prevalent contrast. The measure of contrast used by this adaptation mechanism is commonly assumed to be the standard deviation of light intensities relative to the mean ( root-mean-square contrast). A number of alternatives, however, are possible. For example, the measure of contrast might depend on the absolute deviations relative to the mean, or on the prevalence of the darkest or lightest intensities. We investigated the statistical computation underlying this measure of contrast in the cat's lateral geniculate nucleus, which relays signals from retina to cortex. Borrowing a method from psychophysics, we recorded responses to white noise stimuli whose distribution of intensities was precisely varied. We varied the standard deviation, skewness, and kurtosis of the distribution of intensities while keeping the mean luminance constant. We found that gain strongly depends on the standard deviation of the distribution. At constant standard deviation, moreover, gain is invariant to changes in skewness or kurtosis. These findings held for both ON and OFF cells, indicating that the measure of contrast is independent of the range of stimulus intensities signaled by the cells. These results confirm the long-held assumption that contrast gain control computes root-mean-square contrast. They also show that contrast gain control senses the full distribution of intensities and leaves unvaried the relative responses of the different cell types. The advantages to visual processing of this remarkably specific computation are not entirely known.