Hofmann M I, Barnes C S, Hallett P E
Department of Zoology, University of Toronto, Canada.
Vision Res. 1990;30(10):1453-66. doi: 10.1016/0042-6989(90)90026-h.
Scotopic contrast sensitivity was measured near 20 deg retinal eccentricity for briefly flashed (10 or 20 msec) sine-wave gratings presented in darkness to dark-adapted subjects. For very low spatial frequencies (0.2-0.5 c/deg), curves of contrast sensitivity vs luminous energy show evidence of a low rod plateau and a high scotopic region, with an intervening transition at around -2 to -2.5 log scot td sec. Similar measurements made using long flashed or flickering gratings do not show a plateau. The results suggest that vision in the low rod region is impaired for brief flashes. For the briefly flashed stimuli, curves of contrast sensitivity versus spatial frequency in the low region were best fit by simple Gaussian functions with a variable centre size (sigma c = 0.5----0.25 deg), size decreasing with increasing flash energy. Difference-of-Gaussian functions with constant centre size (sigma c = 0.25 deg) provided the best fit in the high region. Overt input from the cones and grating area artefacts are excluded by appropriate tests. Calculation of photon flux into the receptive field centres suggests that signal compression in P alpha ganglion cells contributes to the low rod plateau.
在黑暗环境中，对暗适应的受试者，在视网膜偏心度约20度处测量了对短暂闪光（10或20毫秒）正弦波光栅的暗视对比敏感度。对于非常低的空间频率（0.2 - 0.5周/度），对比敏感度与发光能量的曲线显示出低视杆平台和高暗视区域的证据，在大约-2至-2.5 log暗视td秒处有一个中间过渡。使用长闪光或闪烁光栅进行的类似测量未显示出平台。结果表明，在低视杆区域，短暂闪光的视觉受到损害。对于短暂闪光刺激，低区域中对比敏感度与空间频率的曲线通过具有可变中心大小（σc = 0.5 - 0.25度）的简单高斯函数最佳拟合，中心大小随闪光能量增加而减小。具有恒定中心大小（σc = 0.25度）的高斯差分函数在高区域提供了最佳拟合。通过适当的测试排除了来自视锥细胞的明显输入和光栅面积伪影。对视感受野中心的光子通量计算表明，Pα神经节细胞中的信号压缩导致了低视杆平台。
