Fujimoto Kiyoshi, Yagi Akihiro
Department of Psychology, Kwansei Gakuin University, Uegahara 1-1-155, Nishinomiya, Hyogo, 662-8501, Japan.
Perception. 2008;37(12):1783-9. doi: 10.1068/p5933.
When a movie presents a person walking, the background appears to move in the direction opposite to the person's gait. This study verified this backscroll illusion by presenting a point-light walker against a background of a random-dot cinematogram (RDC). The RDC consisted of some signal dots moving coherently either leftward or rightward among other noise dots moving randomly. The method of constant stimuli was used to vary the RDC in motion coherence from trial to trial by manipulating the direction and percentage of the signal dots. Six observers judged the perceived direction of coherent motion in a two-alternative forced-choice procedure. Response rates for coherent motion perception in the direction opposite to walking were evaluated as a function of motion coherence. The results showed that the psychometric function shifted toward the direction determined by a bias in the opposite direction to the walker. The mean threshold was about half as high as that in a control condition in which the positions of the point-lights were scrambled to impair the recognition of the walker. The results demonstrate that biological motion noticeably affects the appearance of motion coherence in the background.
当一部电影呈现一个人行走时，背景似乎会朝着与人物步态相反的方向移动。本研究通过在随机点电影图（RDC）背景下呈现一个点光行走者来验证这种后卷错觉。RDC由一些在其他随机移动的噪声点中向左或向右连贯移动的信号点组成。采用恒定刺激法，通过操纵信号点的方向和百分比，在每次试验中改变RDC的运动连贯性。六位观察者在二选一的强制选择程序中判断连贯运动的感知方向。将与行走方向相反的连贯运动感知的反应率作为运动连贯性的函数进行评估。结果表明，心理测量函数朝着与行走者相反方向的偏差所确定的方向移动。平均阈值约为对照条件下的一半，在对照条件下，点光的位置被打乱以损害对行走者的识别。结果表明，生物运动显著影响背景中运动连贯性的外观。
