Georgeson M A
Department of Psychology, University of Bristol, UK.
Spat Vis. 1985;1(2):103-12. doi: 10.1163/156856885x00125.
Perceived contrast was assessed by contrast-matching between adjacent sinusoidal gratings of the same spatial frequency (3 cycles/degree), before and after adaptation to gratings of various contrasts. On logarithmic axes, the effect of adaptation was large for test contrasts below the adapting contrast, but absent for test contrasts higher than the adapting contrast. This result rules out a simple gain-reduction hypothesis, in which adaptation would attenuate all test contrasts by the same proportion. Instead, results for all combinations of adapting and test contrast levels (including threshold elevation) conformed fairly closely to a simple subtractive rule: any test contrast presented after adaptation behaved as if one-third of the adapting contrast were subtracted from it. Though not exact, this may be a useful descriptive rule. Deviations from the simple rule may be explained by increased variance in the visual response at high adapting contrasts, combined with nonlinearity at low test contrasts. A subtractive effect at the psychophysical level does not necessarily conflict with evidence for contrast gain reduction at the single-cell level.
通过在适应不同对比度光栅之前和之后，对相同空间频率（3 周/度）的相邻正弦光栅进行对比度匹配来评估感知对比度。在对数轴上，对于低于适应对比度的测试对比度，适应效果显著，但对于高于适应对比度的测试对比度则不存在。这一结果排除了简单的增益降低假说，即在该假说中，适应会以相同比例减弱所有测试对比度。相反，适应和测试对比度水平的所有组合（包括阈值升高）的结果相当紧密地符合一个简单的减法规则：适应后呈现的任何测试对比度，其表现就好像从它中减去了三分之一的适应对比度。虽然并不精确，但这可能是一个有用的描述性规则。与简单规则的偏差可能是由于在高适应对比度下视觉反应的方差增加，以及在低测试对比度下的非线性共同导致的。心理物理学水平上的减法效应不一定与单细胞水平上对比度增益降低的证据相冲突。
