Vincent A, Regan D
Department of Psychology, York University, Ontario, Canada.
Perception. 1995;24(5):491-9. doi: 10.1068/p240491.
Subjects were presented with a set of 216 test gratings in random order. Each had a different combination of orientation, spatial frequency, and contrast. For each test grating, subjects were instructed to judge whether or not orientation was clockwise of the mean of the stimulus set, whether or not spatial frequency was higher than the mean of the stimulus set, and whether or not contrast was higher than the mean of the stimulus set. Each of the three sets of button presses was analyzed with respect to each of the three parameters, giving nine psychometric functions from one response set. It is concluded that, for gratings of high visibility, changes of orientation, spatial frequency, and contrast are encoded independently and in parallel, at least for small changes in these three visual parameters. In another experiment only one of the three parameters was varied at a time. Neither orientation-discrimination threshold, nor spatial-frequency-discrimination threshold, nor contrast-discrimination threshold was appreciably, if at all, lower than when all three parameters were varied simultaneously. It is concluded that interactions between the processing of small changes in orientation, spatial frequency, and contrast are negligible when all three are processed simultaneously. It is proposed that trial-to-trial variations of orientation, spatial frequency, and contrast are unconfounded by opponent processing within a population of neurons, each of which confounds the three variables.
受试者以随机顺序观看一组216个测试光栅。每个光栅都有不同的方向、空间频率和对比度组合。对于每个测试光栅，受试者被要求判断方向是否顺时针于刺激集的平均值，空间频率是否高于刺激集的平均值，以及对比度是否高于刺激集的平均值。对三组按键中的每一组都针对三个参数中的每一个进行分析，从一个反应集中得出九个心理测量函数。得出的结论是，对于高可见度的光栅，方向、空间频率和对比度的变化至少在这三个视觉参数的小变化范围内是独立且并行编码的。在另一个实验中，一次仅改变三个参数中的一个。无论方向辨别阈值、空间频率辨别阈值还是对比度辨别阈值，即使有的话，也不会明显低于三个参数同时变化时的阈值。得出的结论是，当方向、空间频率和对比度的小变化同时进行处理时，它们之间的相互作用可以忽略不计。有人提出，方向、空间频率和对比度的逐次试验变化不会因神经元群体内的拮抗处理而混淆，而每个神经元群体都会混淆这三个变量。
