MacLeod D I, He S
Department of Psychology, University of California, San Diego, La Jolla 92093-0109.
Nature. 1993 Jan 21;361(6409):256-8. doi: 10.1038/361256a0.
Using a laser interferometer we can create grating patterns of high optical contrast (interference fringes) directly on the retina. With coarse fringe patterns, the alternating light and dark bars of the pattern can be seen, but the bars of the finest fringes are not subjectively resolved. We report here that when we rapidly modulate the contrast of a fine fringe pattern (keeping overall luminance constant), observers experience flicker, even if the fringes are too finely spaced to be perceived as a grating. For this flicker to be seen, the pattern needs to be resolvable by the photoreceptors themselves, but not necessarily by later stages of visual processing. It can be explained if, in man, signals associated with individual cone receptors do not depend linearly on light intensity, but instead are scaled by a fast sensitivity-regulating or light-adaptation mechanism. Contrast-modulation flicker is not demonstrable in rod vision; rod vision therefore lacks such a local adaptation process.
使用激光干涉仪，我们可以直接在视网膜上创建具有高光学对比度的光栅图案（干涉条纹）。对于粗糙的条纹图案，可以看到图案中明暗交替的条纹，但最精细条纹的条纹无法被主观分辨。我们在此报告，当我们快速调制精细条纹图案的对比度（保持整体亮度不变）时，观察者会体验到闪烁，即使条纹间距过细以至于无法被感知为光栅。为了看到这种闪烁，图案需要能够被光感受器自身分辨，但不一定需要视觉处理的后期阶段来分辨。如果在人类中，与单个视锥感受器相关的信号并非线性地依赖于光强度，而是通过一种快速的灵敏度调节或光适应机制进行缩放，那么这一现象就可以得到解释。对比度调制闪烁在杆状视觉中无法得到证实；因此，杆状视觉缺乏这样一种局部适应过程。
