Bowns L
Psychology Department, University of Nottingham, U.K.
Vision Res. 1996 Nov;36(22):3685-94. doi: 10.1016/0042-6989(96)00082-x.
When two moving sinusoidal gratings, with similar spatial frequency, contrast, phase, but different orientation are combined to form a plaid, their perceived direction of motion has been predicted by the intersection of constraints rule (IOC) (Adelson & Movshon, Nature, 300, 523-525, 1982). However, at short durations (60 msec) the direction of perceived motion has been predicted by the vector sum direction for "Type II" plaids (Yo & Wilson, Vision Research, 32, 1, 1992). Type II plaids are the set of plaids where the components are both located on one side of the resultant computed using the IOC rule. Yo and Wilson suggest that the vector sum direction is observed for Type II plaids at short durations because non-Fourier information is not available and direction is computed from Fourier information only. The first experiment in this study replicates the original Yo and Wilson result using similar stimuli but a simpler task; perceived direction was measured using a direction discrimination task instead of the method of adjustment used by Yo and Wilson. The second experiment provides evidence against generalizing the result to all Type II plaids. A systematic set of type II plaids that varied only in terms of the orientation of the second component provided an ideal set because their predicted motion direction followed very different patterns when predicted by the IOC and vector sum computations. The results obtained were predicted more accurately by the IOC than the vector sum. Experiment 3 provides further evidence that movement in the vector sum direction is not a general property of type II plaids. A small change to the velocity of one of the components of a plaid previously perceived in the vector sum direction had the effect of shifting the perceived motion in the IOC direction, despite increasing the difference between the IOC and VS predictions. This result is not consistent with Yo and Wilson's hypothesis that Type II plaids move in the vector sum direction because of a temporal delay between Fourier and non-Fourier information. Computational analysis of the stimuli used in both the current and original experiments revealed a possible explanation of the results in terms of a contribution from local feature tracking rather than a vector sum operation.
当两个具有相似空间频率、对比度、相位但方向不同的移动正弦光栅组合形成一个方格图案时，它们的感知运动方向已由约束交叉规则（IOC）预测（阿德尔森和莫夫尚，《自然》，第300卷，第523 - 525页，1982年）。然而，在短持续时间（60毫秒）内，“II型”方格图案的感知运动方向已由矢量和方向预测（约和威尔逊，《视觉研究》，第32卷，第1期，1992年）。II型方格图案是指其组成部分都位于使用IOC规则计算出的合向量的一侧的方格图案集合。约和威尔逊认为，在短持续时间内观察到II型方格图案的矢量和方向，是因为非傅里叶信息不可用，方向仅从傅里叶信息计算得出。本研究的第一个实验使用类似的刺激但更简单的任务重复了约和威尔逊的原始结果；使用方向辨别任务而不是约和威尔逊所使用的调整方法来测量感知方向。第二个实验提供了反对将该结果推广到所有II型方格图案的证据。一组仅在第二个组成部分的方向上有所变化的系统的II型方格图案提供了一个理想的集合，因为当通过IOC和矢量和计算进行预测时，它们预测的运动方向遵循非常不同的模式。通过IOC比通过矢量和更准确地预测了所获得的结果。实验3提供了进一步的证据，表明在矢量和方向上的运动不是II型方格图案的一般属性。对一个先前在矢量和方向上被感知的方格图案的一个组成部分的速度进行小的改变，尽管增加了IOC和VS预测之间的差异，但却使感知运动向IOC方向移动。这一结果与约和威尔逊的假设不一致，即II型方格图案在矢量和方向上移动是因为傅里叶信息和非傅里叶信息之间存在时间延迟。对当前和原始实验中使用的刺激进行的计算分析揭示了一个可能的结果解释，即局部特征跟踪的贡献而非矢量和操作。
