Tucker J, Charman W N
Am J Optom Physiol Opt. 1986 Jan;63(1):58-70. doi: 10.1097/00006324-198601000-00010.
It is well-known that the accommodative response of the visual system to Snellen letters and other targets of wide spatial bandwidth becomes less accurate as the luminance is lowered from photopic to scotopic levels, a constant state of "night myopia" eventually being reached. The present study seeks to understand this behavior in terms of the responses to the single-frequency, sinusoidal grating, Fourier components of such targets, for a constant, 80% object modulation. The focal range over which sinusoidal gratings can be detected is first investigated as a function of grating frequency and luminance; this range diminishes as the luminance is lowered. These data are then related to measurements of the accommodative response to similar gratings in the mesopic luminance range (10(-2.5) to 10 cd/m2). The response is less accurate for gratings of low spatial frequency. It appears that, provided that any grating can be detected, changes in luminance generally have only a relatively small effect on the associated accommodative response. However, low spatial frequency gratings can be detected at much lower luminance levels than higher spatial frequency gratings. The effects observed with targets of wide spatial bandwidth may thus be largely ascribed to the inability of the visual system to use higher spatial frequency information as the luminance is lowered.
众所周知，随着亮度从明视觉水平降低到暗视觉水平，视觉系统对斯内伦字母和其他具有宽空间带宽的目标的调节反应会变得不那么准确，最终会达到一种持续的“夜间近视”状态。本研究旨在通过对单频正弦光栅（此类目标的傅里叶分量）的反应，在物体调制恒定为80%的情况下，来理解这种行为。首先研究了正弦光栅可被检测到的焦距范围与光栅频率和亮度的关系；随着亮度降低，该范围会减小。然后将这些数据与在中间视觉亮度范围（10^(-2.5)至10坎德拉每平方米）内对类似光栅的调节反应测量结果相关联。对于低空间频率的光栅，反应不太准确。似乎只要任何光栅都能被检测到，亮度变化通常对相关的调节反应只有相对较小的影响。然而，低空间频率光栅能在比高空间频率光栅低得多的亮度水平下被检测到。因此，在具有宽空间带宽的目标上观察到的效应可能主要归因于随着亮度降低，视觉系统无法利用更高空间频率的信息。
