Stockman Andrew, Langendörfer Micha, Sharpe Lindsay T
Institute of Ophthalmology, University College London, London, UK.
J Vis. 2007 Feb 22;7(3):4. doi: 10.1167/7.3.4.
The cone-driven visual system is able to regulate its sensitivity effectively from twilight to bright sunlight. On the basis of a novel combination of short-wavelength-sensitive (S-) cone measurements of temporal sensitivity and temporal delay, we show that S-cone light adaptation is achieved not only by trading unwanted sensitivity for speed but also by an additional process that counterintuitively increases the overall sensitivity as the light level rises. Our results are consistent with comparable middle-wavelength-sensitive (M-) cone measurements made in protanopic observers and can be accounted for by the same two-parameter model developed to account for the M-cone data (A. Stockman, M. Langendörfer, H. E. Smithson, & L. T. Sharpe, 2006). Each stage of the model can be linked to molecular mechanisms occurring within the photoreceptor: the speeding up to increases in the rates of decay of active and messenger molecules, the unexpected sensitivity increases to increased rates of molecular resynthesis and changes in channel sensitivity, and the sensitivity decreases to bleaching. Together, these mechanisms act to maintain vision in an optimal operating range and to protect it from overload.
视锥细胞驱动的视觉系统能够有效地调节其敏感度，从黄昏到明亮的阳光照射下都能适应。基于对短波长敏感（S）视锥细胞的时间敏感度和时间延迟测量的一种新组合，我们发现S视锥细胞的光适应不仅是通过用不需要的敏感度换取速度来实现的，而且还通过一个额外的过程来实现，这个过程与直觉相反，即随着光照水平的升高，整体敏感度会增加。我们的结果与在红绿色盲观察者中进行的类似的中波长敏感（M）视锥细胞测量结果一致，并且可以用为解释M视锥细胞数据而开发的相同的双参数模型来解释（A. 斯托克曼、M. 朗根多费尔、H. E. 史密森和L. T. 夏普，2006年）。该模型的每个阶段都可以与光感受器内发生的分子机制联系起来：速度加快与活性分子和信使分子衰变率的增加有关，意外的敏感度增加与分子再合成率的增加和通道敏感度的变化有关，而敏感度降低与漂白有关。这些机制共同作用，以维持视觉在最佳操作范围内，并保护其免受过载。
