Webster M A, De Valois K K, Switkes E
Department of Psychology, University of California, Berkeley 94720.
J Opt Soc Am A. 1990 Jun;7(6):1034-49. doi: 10.1364/josaa.7.001034.
We have examined the accuracy of orientation and spatial-frequency discrimination for sine-wave gratings that vary in either luminance or color. The equiluminant chromatic gratings were modulated along either a tritanopic confusion axis (so that they were detectable on the basis of activity in only the short-wavelength-sensitive cones) or an axis of constant short-wavelength-sensitive cone excitation (so that they could be detected on the basis of opposing activity in only the long- and medium-wavelength-sensitive cones). Grating contrasts ranged from the detection threshold to the highest levels that we could produce; the contrasts of the luminance and color patterns were equated for equal multiples of their respective detection thresholds. Discrimination thresholds for all patterns showed a similar dependence on stimulus contrast, rising sharply at low contrasts and becoming nearly asymptotic at moderate contrasts. However, even at threshold contrasts, observers could still reliably discriminate sufficiently large differences in the orientation or spatial frequency of all patterns, and they could also reliably identify the type of variation (luminance or which color) defining the grafting. For most conditions the discrimination thresholds did not differ from the two types of color grafting and reached values as low as 1 deg (orientation) or 4% (spatial frequency). Thus observers were able to make accurate spatial judgments on the basis of either type of chromatic information. However, these thresholds were slightly but consistently higher than the thresholds for comparable luminance graftings. This difference in the color and luminance discrimination thresholds may reflect somewhat coarser orientation and spatial-frequency selectivity in the mechanisms encoding the chromatic patterns.
我们研究了亮度或颜色变化的正弦波光栅的方向和空间频率辨别精度。等亮度的彩色光栅沿着一条蓝黄色混淆轴进行调制（这样它们仅基于短波敏感视锥细胞的活动就能被检测到），或者沿着一条恒定的短波敏感视锥细胞兴奋轴进行调制（这样它们仅基于长波和中波敏感视锥细胞的相反活动就能被检测到）。光栅对比度范围从检测阈值到我们能产生的最高水平；亮度和颜色图案的对比度在各自检测阈值的相同倍数下被等同。所有图案的辨别阈值对刺激对比度呈现出相似的依赖性，在低对比度时急剧上升，在中等对比度时接近渐近线。然而，即使在阈值对比度下，观察者仍能可靠地区分所有图案在方向或空间频率上足够大的差异，并且他们也能可靠地识别定义光栅的变化类型（亮度或哪种颜色）。在大多数情况下，两种类型的彩色光栅的辨别阈值没有差异，达到低至1度（方向）或4%（空间频率）的值。因此，观察者能够基于任何一种颜色信息做出准确的空间判断。然而，这些阈值略高于但始终高于可比亮度光栅的阈值。颜色和亮度辨别阈值的这种差异可能反映了编码彩色图案的机制中方向和空间频率选择性稍显粗糙。
