Allard Rémy, Faubert Jocelyn
Visual Psychophysics and Perception Laboratory, Université de Montréal, Montréal, Québec, Canada.
J Vis. 2014 Jul 3;14(8):2. doi: 10.1167/14.8.2.
To conclude that there is a dedicated color motion system, the hypothesis that the luminance motion pathway is processing color motion due to some nonlinearity must be rejected. Many types of nonlinearities have been considered. Cavanagh and Anstis (1991) considered interunit variability in equiluminance, but they found that adding a color-defined modulation to a luminance-defined drifting modulation increased the contribution to motion. This color contribution to motion cannot be due to interunit variability in equiluminance alone because such a luminance artifact would increase the effective luminance contrast for some luminance-sensitive units and decrease it for the others, resulting in no additional contribution to motion on average. Cavanagh and Anstis considered this color contribution to motion as evidence of a dedicated color motion system, but here we show that such a color contribution to motion varies with the phase difference between the luminance and color modulations, which would not be expected if luminance- and color-defined motion were processed separately. Specifically, the contribution to motion was greater when the luminance and color modulations were aligned (i.e., 0 degrees or 180 degrees phase difference), than when they were not (90 degrees or 270 degrees phase difference). Such a luminance-color phase interaction was also observed when spatially interleaving luminance and color information, which suggests that the interaction occurs after some spatial integration (i.e., not at the photoreceptors). To our knowledge, this luminance-color phase interaction cannot be explained by any previously considered nonlinearity. However, it can be explained by an expansive nonlinearity occurring before the summation of the L- and M-cone pathways (i.e., before ganglion cells) and after some spatial integration (i.e., after the photoreceptors). We conclude that there is a nonlinearity that has not been considered before, enabling some color motion processing by the luminance motion system.
要得出存在专门的颜色运动系统这一结论，就必须摒弃亮度运动通路因某种非线性而处理颜色运动的假设。人们已经考虑了多种类型的非线性。卡瓦纳和安斯蒂斯（1991年）考虑了等亮度条件下的单元间变异性，但他们发现，在以亮度定义的漂移调制上添加颜色定义的调制会增加对运动的贡献。这种对运动的颜色贡献不可能仅仅归因于等亮度条件下的单元间变异性，因为这样的亮度伪像会使一些对亮度敏感的单元的有效亮度对比度增加，而使其他单元的有效亮度对比度降低，平均而言不会对运动产生额外贡献。卡瓦纳和安斯蒂斯将这种对运动的颜色贡献视为存在专门颜色运动系统的证据，但我们在此表明，这种对运动的颜色贡献会随亮度调制和颜色调制之间的相位差而变化，如果亮度定义的运动和颜色定义的运动是分别处理的，这是不会出现的情况。具体而言，当亮度调制和颜色调制对齐时（即相位差为0度或180度），对运动的贡献大于它们未对齐时（相位差为90度或270度）。当在空间上交错亮度和颜色信息时，也观察到了这种亮度 - 颜色相位相互作用，这表明这种相互作用发生在某种空间整合之后（即不在光感受器处）。据我们所知，这种亮度 - 颜色相位相互作用无法用之前考虑的任何非线性来解释。然而，它可以通过在L锥和M锥通路求和之前（即神经节细胞之前）且在某种空间整合之后（即光感受器之后）发生的一种扩展非线性来解释。我们得出结论，存在一种之前未被考虑的非线性，使得亮度运动系统能够进行一些颜色运动处理。
