Raphael Sabine, MacLeod Donald I A
Department of Psychology, University of California, San Diego, La Jolla, CA, USA.
J Vis. 2011 Aug 25;11(9):14. doi: 10.1167/11.9.14.
We measured the relative contribution of rods and cones to luminance across a range of photopic, mesopic, and scotopic adaptation levels and at various retinal eccentricities. We isolated the luminance channel by setting motion-based luminance nulls (minimum motion photometry) using annular stimuli. Luminance nulls between differently colored stimuli require equality in a weighted sum of rod and cone excitations. The relative cone weight increases smoothly from the scotopic range, where rods dominate, to photopic levels, where rod influence becomes negligible. The change from rod to cone vision does not occur uniformly over the visual field. The more peripheral the stimulus location, the higher is the light level required for cones to participate strongly. The relative cone contribution can be described by a sigmoid function of intensity, with two parameters that each depend on the eccentricity and spatial frequency of the stimulus. One parameter determines the "meso-mesopic" luminance--the center of the mesopic range, at which rod and cone contributions are balanced. This increases with eccentricity, reflecting an increase in the meso-mesopic luminance from 0.04 scotopic cd/m(2) at 2° eccentricity to 0.44 scotopic cd/m(2) at 18°. The second parameter represents the slope of the log-log threshold-versus-intensity curve (TVI curve) for rod vision. This parameter inversely scales the width of the mesopic range and increases only slightly with eccentricity (from 0.73 at 2° to 0.78 for vision at 18° off-axis).
我们测量了在一系列明视觉、中间视觉和暗视觉适应水平下以及不同视网膜偏心度时，视杆细胞和视锥细胞对亮度的相对贡献。我们通过使用环形刺激设置基于运动的亮度零点（最小运动光度法）来分离亮度通道。不同颜色刺激之间的亮度零点要求视杆细胞和视锥细胞激发的加权总和相等。视锥细胞的相对权重从暗视觉范围（视杆细胞占主导）到明视觉水平（视杆细胞的影响可忽略不计）平稳增加。从视杆细胞视觉到视锥细胞视觉的转变并非在整个视野中均匀发生。刺激位置越周边，视锥细胞强烈参与所需的光水平就越高。视锥细胞的相对贡献可以用强度的S形函数来描述，有两个参数，每个参数都取决于刺激的偏心度和空间频率。一个参数决定“中间-中间视觉”亮度——中间视觉范围的中心，此时视杆细胞和视锥细胞的贡献达到平衡。这个值随着偏心度增加，反映出中间-中间视觉亮度从2°偏心度时的0.04暗视觉坎德拉每平方米增加到18°时的0.44暗视觉坎德拉每平方米。第二个参数代表视杆细胞视觉的对数-对数阈值与强度曲线（TVI曲线）的斜率。这个参数反比例缩放中间视觉范围的宽度，并且仅随着偏心度略有增加（从2°时的0.73增加到离轴18°视觉时的0.78）。
