Kim Yeon Jin, Gheiratmand Mina, Mullen Kathy T
McGill Vision Research, Department of Ophthalmology, McGill University, Montreal, Quebec, Canada.
J Vis. 2013 May 28;13(6):15. doi: 10.1167/13.6.15.
Cross-orientation masking (XOM) occurs when the detection of a test grating is masked by a superimposed grating at an orthogonal orientation, and is thought to reveal the suppressive effects mediating contrast normalization. Medina and Mullen (2009) reported that XOM was greater for chromatic than achromatic stimuli at equivalent spatial and temporal frequencies. Here we address whether the greater suppression found in binocular color vision originates from a monocular or interocular site, or both. We measure monocular and dichoptic masking functions for red-green color contrast and achromatic contrast at three different spatial frequencies (0.375, 0.75, and 1.5 cpd, 2 Hz). We fit these functions with a modified two-stage masking model (Meese & Baker, 2009) to extract the monocular and interocular weights of suppression. We find that the weight of monocular suppression is significantly higher for color than achromatic contrast, whereas dichoptic suppression is similar for both. These effects are invariant across spatial frequency. We then apply the model to the binocular masking data using the measured values of the monocular and interocular sources of suppression and show that these are sufficient to account for color binocular masking. We conclude that the greater strength of chromatic XOM has a monocular origin that transfers through to the binocular site.
当测试光栅的检测被正交方向上叠加的光栅掩盖时，就会出现交叉方向掩蔽（XOM），人们认为它揭示了介导对比度归一化的抑制作用。梅迪纳和马伦（2009年）报告称，在等效的空间和时间频率下，彩色刺激的XOM比非彩色刺激的XOM更大。在这里，我们探讨在双眼颜色视觉中发现的更大抑制作用是源于单眼部位还是双眼间部位，或者两者皆有。我们测量了三种不同空间频率（0.375、0.75和1.5周/度，2赫兹）下红绿色对比度和非彩色对比度的单眼和双眼掩蔽函数。我们用一个修改后的两阶段掩蔽模型（米斯和贝克，2009年）拟合这些函数，以提取单眼和双眼间的抑制权重。我们发现，颜色对比度的单眼抑制权重显著高于非彩色对比度，而双眼间抑制在两者中相似。这些效应在空间频率上是不变的。然后，我们使用单眼和双眼间抑制源的测量值将该模型应用于双眼掩蔽数据，并表明这些足以解释颜色双眼掩蔽。我们得出结论，彩色XOM更强的强度源于单眼，且会传递到双眼部位。
