UCL Institute of Ophthalmology, University College London, London, England.
PLoS One. 2019 Aug 7;14(8):e0220358. doi: 10.1371/journal.pone.0220358. eCollection 2019.
The range of c. 1012 ambient light levels to which we can be exposed massively exceeds the <103 response range of neurons in the visual system, but we can see well in dim starlight and bright sunlight. This remarkable ability is achieved largely by a speeding up of the visual response as light levels increase, causing characteristic changes in our sensitivity to different rates of flicker. Here, we account for over 65 years of flicker-sensitivity measurements with an elegantly-simple, physiologically-relevant model built from first-order low-pass filters and subtractive inhibition. There are only two intensity-dependent model parameters: one adjusts the speed of the visual response by shortening the time constants of some of the filters in the direct cascade as well as those in the inhibitory stages; the other parameter adjusts the overall gain at higher light levels. After reviewing the physiological literature, we associate the variable gain and three of the variable-speed filters with biochemical processes in cone photoreceptors, and a further variable-speed filter with processes in ganglion cells. The variable-speed but fixed-strength subtractive inhibition is most likely associated with lateral connections in the retina. Additional fixed-speed filters may be more central. The model can explain the important characteristics of human flicker-sensitivity including the approximate dependences of low-frequency sensitivity on contrast (Weber's law) and of high-frequency sensitivity on amplitude ("high-frequency linearity"), the exponential loss of high-frequency sensitivity with increasing frequency, and the logarithmic increase in temporal acuity with light level (Ferry-Porter law). In the time-domain, the model can account for several characteristics of flash sensitivity including changes in contrast sensitivity with light level (de Vries-Rose and Weber's laws) and changes in temporal summation (Bloch's law). The new model provides fundamental insights into the workings of the visual system and gives a simple account of many visual phenomena.
我们可能会暴露在环境光水平约为 1012 的范围内，这大大超过了视觉系统中神经元的<103 响应范围，但我们可以在昏暗的星光和明亮的阳光下看得很清楚。这种非凡的能力主要是通过随着光水平的增加加快视觉响应来实现的，这导致了我们对不同闪烁率的敏感性的特征变化。在这里，我们用一个优雅简单的模型来解释超过 65 年的闪烁敏感性测量，该模型由一阶低通滤波器和减法抑制构建而成。只有两个与强度相关的模型参数：一个通过缩短直接级联中一些滤波器和抑制级中的滤波器的时间常数来调整视觉响应的速度；另一个参数在较高光水平下调整整体增益。在回顾生理学文献之后，我们将可变增益和三个可变速度滤波器与视锥感光细胞中的生化过程相关联，而另一个可变速度滤波器与神经节细胞中的过程相关联。可变速度但固定强度的减法抑制很可能与视网膜中的侧连接有关。额外的固定速度滤波器可能更集中。该模型可以解释人类闪烁敏感性的重要特征，包括低频敏感性对对比度的近似依赖性（韦伯定律）和高频敏感性对幅度的依赖性（“高频线性”），高频敏感性随频率的指数损失，以及光水平对数增加时的时间精度（Ferry-Porter 定律）。在时域中，该模型可以解释闪光敏感性的几个特征，包括随光水平变化的对比度敏感性（de Vries-Rose 和 Weber 定律）和时间总和的变化（Bloch 定律）。新模型为视觉系统的工作原理提供了基本的见解，并简单地解释了许多视觉现象。
