Garcia-Suarez Luis, Mullen Kathy T
McGill Vision Research, Department of Ophthalmology, McGill University, Montreal, Quebec, Canada.
J Vis. 2013 Jun 13;13(7):10. doi: 10.1167/13.7.10.
We investigate whether there are second-order form and motion mechanisms in human color vision. Second-order stimuli are contrast modulations of a noise carrier. The contrast envelopes are static Gabors of different spatial frequencies (0.125-1 cycles/°) or drifting Gabors of different temporal frequencies (0.25 cycles/°, 0.5-4 Hz). Stimuli are isoluminant red-green or achromatic. Second-order form processing is measured using a simultaneous 2IFC (two-interval forced-choice) detection and orientation identification task, and direction identification is used for second-order motion processing. We find that for simple detection thresholds, chromatic performance is as good or better than achromatic performance, whereas for both motion and form tasks, chromatic performance is poorer than achromatic. Chromatic second-order form perception is very poor across all spatial and temporal frequencies measured and has a lowpass contrast modulation sensitivity function with a spatial cutoff of 1 cycle/° and temporal cutoff of 4 Hz. Chromatic second-order motion sensitivity is even poorer than for form and typically is limited to 1-2 Hz. To determine whether this residual motion processing might be based on feature tracking, we used the pedestal paradigm of Lu and Sperling (1995). We find that adding a static pedestal of the same spatial frequency as the drifting Gabor envelope, with its contrast set to 1-2 times its detection threshold, impairs motion direction performance for the chromatic stimuli but not the achromatic. This suggests that the motion of second-order chromatic stimuli is not processed by a second-order system but by a third-order, feature-tracking system, although a genuine second-order motion system exists for achromatic stimuli.
我们研究了人类颜色视觉中是否存在二阶形式和运动机制。二阶刺激是噪声载体的对比度调制。对比度包络是不同空间频率（0.125 - 1周/度）的静态加博尔函数或不同时间频率（0.25周/度，0.5 - 4赫兹）的漂移加博尔函数。刺激为等亮度的红 - 绿或非彩色。二阶形式处理通过同时进行的二区间迫选（2IFC）检测和方向识别任务来测量，方向识别用于二阶运动处理。我们发现，对于简单检测阈值，彩色性能与非彩色性能相当或更好，而对于运动和形式任务，彩色性能均比非彩色差。在所有测量的空间和时间频率上，彩色二阶形式感知都非常差，并且具有低通对比度调制灵敏度函数，空间截止频率为1周/度，时间截止频率为4赫兹。彩色二阶运动灵敏度甚至比形式感知更差，通常限于1 - 2赫兹。为了确定这种残余运动处理是否可能基于特征跟踪，我们使用了Lu和Sperling（1995）的基座范式。我们发现，添加一个与漂移加博尔包络具有相同空间频率的静态基座，其对比度设置为检测阈值的1 - 2倍，会损害彩色刺激的运动方向性能，但不会损害非彩色刺激的运动方向性能。这表明二阶彩色刺激的运动不是由二阶系统处理，而是由三阶特征跟踪系统处理，尽管对于非彩色刺激存在真正的二阶运动系统。
