Linearity and Non-linearity in the Retinal Light Response

这项为期三年的持续拨款是关于眼睛视觉反应机制的。眼睛的视网膜是一种感觉组织，包含与几种神经细胞相连的感光细胞。人类视觉处理的最简单的亚单位是受到光刺激时，视网膜上一片均匀的亮斑所产生的反应。这种对光的反应并不简单，而是受到一系列事件的影响，这些事件可以用数学模型表示为线性和非线性过程。在过去的一个世纪里，已经建立了一套心理物理“定律”，将动态视觉反应与刺激变化联系起来。但其中一些定律意味着刺激效应的简单线性相加，而另一些则意味着刺激效应不能线性相加。这个项目将试图澄清在非极端条件下，视网膜中的哪些处理过程可以满足所有这些规律。视觉系统各层次响应的线性问题，以及线性失效的条件，在揭示视觉处理的顺序中具有互补的意义。一般的方法是使用非线性阶段作为标记来确定每个非线性阶段前后的响应动态。人类观察者将通过测量他们对闪烁灯光强度的感知来接受测试，同时改变刺激的强度和持续时间。第一组实验将检查光导机制的线性，其中光信号首先转换为神经反应信号。高到足以使系统饱和的强度水平将用于探索在饱和之前光化学反应的时间过程。第二个实验将测试当光强有一个大的突然“阶跃”变化时，非线性如何应用于测试脉冲感知阈值的变化。数据分析将包括描述刺激-反应关系的函数的数学建模。这种综合方法是一种新颖而复杂的方法，具有很强的理论成分。研究结果将对许多领域的视觉研究以及其他系统的信息处理模型产生影响。

This continuing grant for three years is on mechanisms of visual response in the eye. The retina of the eye is the sensory tissue containing the photoreceptor cells connected to several kinds of nerve cells. The simplest subunit of human visual processing is the response from a uniform patch of retina illuminated when it is stimulated by light. This response to light is not simple, but subject to a sequence of events which can be modelled mathematically as linear and non-linear processes. Over the past century, a set of psychophysical "laws" have been established to relate dynamic visual responses to stimulus changes over time. But some of these laws imply simple linear addition of stimulus effects, and some imply that the effects cannot be added linearly. This project will try to clarify what kinds of processing in the retina could satisfy all of these laws under non-extreme conditions. The question of linearity of the response at each level of the visual system, and conditions under which the linearity fails have complementary significance un unravelling the sequence of visual processing. The general approach is to use the nonlinear stages as markers to determine the response dynamics before and after each such marker. Human observers will be tested by measuring their perception of the intensity of flickering lights, while varying the intensity and duration of the stimulus. The first set of experiments will examine the linearity of the mechanism of phototransduction, in which the light signal is first converted to a neural response signal. intensity levels high enough to saturate the system will be used to explore the time course of photochemical reactions preceding the saturation. The second experiments will test how non- linearity applies to the change in threshold for perception of a test pulse when there is a large abrupt "step" change in light intensity. Analysis of the data will include mathematical modelling of the functions describing the stimulus-response relationships. This integrated approach is a novel and very sophisticated one, with a strong theoretical component. The results should have impact on visual research in many areas, and on models of information processing in other systems.