Tranchina D, Gordon J, Shapley R M
Nature. 1984;310(5975):314-6. doi: 10.1038/310314a0.
Light adaptation is the adjustment of retinal response properties to variations in ambient illumination. It enables the encoding of visual information over a millionfold intensity range, from moonlight to broad daylight, despite the relatively small dynamic range of response of visual neurones. We have studied the effects of light adaptation on the dynamics and sensitivity of visual responses of neurones in the turtle retina, by measuring the responses of horizontal cells in the retina to light which was modulated with a sinusoidal time course around various mean levels. As a quantitative measure of the transduction from light to neural signals, we calculated the gain of response at each frequency. Gain is defined as the amplitude of the modulated response component divided by the amplitude of light modulation. We report here that the gain (mV photon-1) at low temporal frequencies decreased as the mean light level increased. Over a 2 log-unit range of mean light levels, low-frequency gain was inversely proportional to the mean light level, as in Weber's law. However, at high temporal frequencies, the gain was almost independent of mean light level. Our results are reminiscent of Kelly's results on human temporal-frequency sensitivity in various states of light adaptation. We found that a family of horizontal-cell temporal frequency responses, measured at various mean light levels, could be accounted for by a negative feedback model in which the feedback strength is proportional to mean light level.
光适应是视网膜响应特性对环境光照变化的调整。它能够在从月光到强光的百万倍强度范围内对视觉信息进行编码，尽管视觉神经元的响应动态范围相对较小。我们通过测量海龟视网膜中水平细胞对围绕各种平均水平以正弦时间进程调制的光的响应，研究了光适应对海龟视网膜神经元视觉响应的动力学和敏感性的影响。作为从光到神经信号转导的定量测量，我们计算了每个频率下的响应增益。增益定义为调制响应分量的幅度除以光调制的幅度。我们在此报告，在低时间频率下，增益（mV光子-1）随着平均光水平的增加而降低。在平均光水平的2个对数单位范围内，低频增益与平均光水平成反比，如同韦伯定律所述。然而，在高时间频率下，增益几乎与平均光水平无关。我们的结果让人想起凯利关于人类在各种光适应状态下的时间频率敏感性的结果。我们发现，在各种平均光水平下测量的一组水平细胞时间频率响应，可以由一个负反馈模型来解释，其中反馈强度与平均光水平成正比。
