Boehm A E, MacLeod D I A, Bosten J M
Department of Psychology, University of California, San Diego, CA, USA Vision Science Graduate Group, University of California, Berkeley, CA, USA School of Optometry, University of California, Berkeley, CA, USA.
Department of Psychology, University of California, San Diego, CA, USA.
J Vis. 2014 Nov 20;14(13):19. doi: 10.1167/14.13.19.
For anomalous trichromats, threshold contrasts for color differences captured by the L and M cones and their anomalous analogs are much higher than for normal trichromats. The greater spectral overlap of the cone sensitivities reduces chromatic contrast both at and above threshold. But above threshold, adaptively nonlinear processing might compensate for the chromatically impoverished photoreceptor inputs. Ratios of sensitivity for threshold variations and for color appearance along the two cardinal axes of MacLeod-Boynton chromaticity space were calculated for three groups: normals (N = 15), deuteranomals (N = 9), and protanomals (N = 5). Using a four-alternative forced choice (4AFC) task, threshold sensitivity was measured in four color-directions along the two cardinal axes. For the same participants, we reconstructed perceptual color spaces for the positions of 25 hues using multidimensional scaling (MDS). From the reconstructed color spaces we extracted "color difference ratios," defined as ratios for the size of perceived color differences along the L/(L + M) axis relative to those along the S/(L + M) axis, analogous to "sensitivity ratios" extracted from the 4AFC task. In the 4AFC task, sensitivity ratios were 38% of normal for deuteranomals and 19% of normal for protanomals. Yet, in the MDS results, color difference ratios were 86% of normal for deuteranomals and 67% of normal for protanomals. Thus, the contraction along the L/(L + M) axis shown in the perceptual color spaces of anomalous trichromats is far smaller than predicted by their reduced sensitivity, suggesting that an adaptive adjustment of postreceptoral gain may magnify the cone signals of anomalous trichromats to exploit the range of available postreceptoral neural signals.
对于异常三色视者，由L和M视锥细胞及其异常类似物捕捉到的颜色差异的阈值对比度，比正常三色视者要高得多。视锥细胞敏感度更大的光谱重叠，降低了阈值及阈值以上的颜色对比度。但在阈值以上，自适应非线性处理可能会补偿颜色信息匮乏的光感受器输入。计算了三组人群在麦克劳德 - 博因顿色度空间两个主方向上阈值变化敏感度与颜色外观敏感度的比率：正常人群（N = 15）、绿色异常三色视者（N = 9）和红色异常三色视者（N = 5）。使用四选一强制选择（4AFC）任务，在两个主方向的四个颜色方向上测量阈值敏感度。对于相同的参与者，我们使用多维缩放（MDS）重建了25种色调位置的感知颜色空间。从重建的颜色空间中，我们提取了“色差比率”，定义为沿L/(L + M)轴的感知颜色差异大小与沿S/(L + M)轴的感知颜色差异大小的比率，类似于从4AFC任务中提取的“敏感度比率”。在4AFC任务中，绿色异常三色视者的敏感度比率为正常的38%，红色异常三色视者为正常的19%。然而，在MDS结果中，绿色异常三色视者的色差比率为正常的86%，红色异常三色视者为正常的67%。因此，异常三色视者感知颜色空间中沿L/(L + M)轴的收缩远小于其敏感度降低所预测的程度，这表明感受器后增益的自适应调整可能会放大异常三色视者的视锥细胞信号，以利用可用的感受器后神经信号范围。
