Watamaniuk S N, McKee S P
Psychology Department, Wright State University, Dayton, OH 45435, USA.
Percept Psychophys. 1998 Feb;60(2):191-200. doi: 10.3758/bf03206028.
Human observers can simultaneously encode direction information at two different scales, one local (an individual dot) and one global (the coherent motion of a field of dots distributed over a 10 degrees-diameter display). We assessed whether encoding global motion would preclude the encoding of a local trajectory component and vice versa. In the present experiments, a large number (100-150) of dots were randomly assigned directions in each frame from a uniform distribution of directions spanning a range of 160 degrees to create global motion in a single direction (Williams & Sekuler, 1984). Amidst these background dots, 1 dot moved in a consistent direction (trajectory) for the duration of the display. The direction of this "trajectory dot" was similar to the mean direction of the distribution of directions determining the movement of the background dots. Direction discrimination for both the global motion and the trajectory was measured, using the method of constant stimuli, under precued and postcued partial report conditions. A low- or high-frequency 85-msec tone signaled which motion the subject was to judge. In the precue condition, the tone was presented 200 msec before the onset of the stimulus, whereas in the postcue condition, the tone was presented immediately after the offset of the stimulus. Direction discrimination thresholds for both global and local motion in the postcued condition were not significantly different from those obtained in the precued condition. These results suggest that direction information for both global and local motion is encoded simultaneously and that the observer has access to either motion signal after the presentation of a stimulus.
人类观察者能够同时在两种不同尺度上对方向信息进行编码，一种是局部尺度（单个点），另一种是全局尺度（分布在直径为10度的显示屏上的点场的连贯运动）。我们评估了对全局运动的编码是否会排除对局部轨迹成分的编码，反之亦然。在本实验中，在每一帧中，大量（100 - 150个）的点从跨越160度范围的均匀方向分布中随机分配方向，以创建单一方向的全局运动（Williams和Sekuler，1984）。在这些背景点中，有1个点在显示期间沿一致的方向（轨迹）移动。这个“轨迹点”的方向与决定背景点运动的方向分布的平均方向相似。在预提示和后提示部分报告条件下，使用恒定刺激法测量全局运动和轨迹的方向辨别能力。一个低频或高频的85毫秒音调信号表明受试者要判断哪种运动。在预提示条件下，音调在刺激开始前200毫秒呈现，而在后提示条件下，音调在刺激结束后立即呈现。后提示条件下全局和局部运动的方向辨别阈值与预提示条件下获得的阈值没有显著差异。这些结果表明，全局和局部运动的方向信息是同时编码的，并且观察者在刺激呈现后可以获取任何一种运动信号。
