Verstraten F A, Fredericksen R E, van de Grind W A
Department of Comparative Physiology, Utrecht University, The Netherlands.
Vision Res. 1994 Feb;34(3):349-58. doi: 10.1016/0042-6989(94)90093-0.
Two moving random-pixel arrays (RPAs) were presented simultaneously in the same target field. These RPAs are perceived as two superimposed transparent moving sheets. Although two directions are perceived simultaneously during stimulus presentation, the movement aftereffect (MAE) is unidirectional. The visual system averages both motion signals in the MAE. For motion vectors of equal magnitude and perpendicular direction the MAE direction is the inverse of the sum of both vectors. In the first experiment we measured perceived direction of the MAE of transparent motion for a range of speed combinations. Results indicate that vector summation only predicts the correct MAE direction for combinations of equal speeds. It is suggested that the direction of the MAE of transparent motion is a resultant of the weighted summation of the component inducing vectors. The question then arises what determines the weighting factors. Directional sensitivity and MAE duration of the individual vectors under transparent conditions were measured and used to weigh the vectors and predict the MAE direction of transparent motion. Statistical analyses showed that MAE duration is a better basis to determine the weighting factors predicting the direction of the MAE of transparent motion than component sensitivity. The direction of the MAE of transparent motion thus seems to be determined by the amount of adaptation to the component vectors as reflected by MAE duration. The results suggest that this gain control cannot be located in the individual motion detectors and must be situated at or after some subsequent cooperation stage of the human motion analysis system.
在同一目标区域中同时呈现两个移动的随机像素阵列（RPA）。这些RPA被视为两个叠加的透明移动薄片。尽管在刺激呈现期间同时感知到两个方向，但运动后效（MAE）是单向的。视觉系统在MAE中对两个运动信号进行平均。对于大小相等且方向垂直的运动向量，MAE方向是两个向量之和的相反方向。在第一个实验中，我们测量了一系列速度组合下透明运动的MAE的感知方向。结果表明，向量求和仅能预测相同速度组合下正确的MAE方向。有人提出，透明运动的MAE方向是各分量诱导向量加权求和的结果。于是问题就来了，是什么决定了加权因子。测量了透明条件下各个向量的方向敏感性和MAE持续时间，并用于对向量进行加权，以预测透明运动的MAE方向。统计分析表明，与分量敏感性相比，MAE持续时间是确定预测透明运动MAE方向的加权因子的更好依据。因此，透明运动的MAE方向似乎由MAE持续时间所反映的对各分量向量的适应量决定。结果表明，这种增益控制不可能位于单个运动探测器中，而必须位于人类运动分析系统的某个后续协作阶段或之后。
