Power R P
School of Behavioural Sciences, Macquarie University, Sydney, NSW, Australia.
Perception. 1993;22(9):1099-110. doi: 10.1068/p221099.
Power and Moulden (1992) have proposed a dipole model to account for the apparent movement of gratings in apertures. This includes movement orthogonal to the orientation of the grating, and the barber pole illusion: the illusion that a grating drifting diagonally across a narrow aperture appears to be moving along it. The essence of the model is that movement is signalled by a large number of dipoles, of many orientations and lengths. These dipoles respond if, and only if, one end is stimulated, and then the other. Three experiments intended to test predictions from the model are reported here. In each case a horizontal grating drifted across an aperture and subjects fixated outside the aperture. In experiment 1 subjects fixated just above or below the aperture, and reported the motion aftereffect (MAE) shown by a set of test spots. As predicted by the model, the spots further from the fixation point showed a strong MAE. Experiment 2 combined both viewing conditions of experiment 1, so that test spots above and below the fixation point were viewed simultaneously. The predictions were confirmed, since test spots further from the fixation point exhibited a stronger MAE than test spots closer to the fixation point. In experiment 3 the fixation point in all conditions was below the aperture, and, as predicted, the MAE of a spot near the bottom of the aperture was diagonally upward, although stimulation was horizontal. Again, as predicted, the MAE of a spot in the middle of the aperture appeared to move horizontally. Finally, it was predicted that a test spot at the top of the aperture would appear to move diagonally downwards, but subjects were unable to report unequivocally the direction of motion, since the MAE was occurring too far from the fovea for clear vision. Overall, then, the predictions from the model were confirmed, although there are associated phenomena the model cannot as yet account for.
鲍尔和莫尔登（1992年）提出了一个偶极子模型，以解释光栅在孔径中的明显移动。这包括与光栅方向正交的移动，以及理发店旋转灯柱错觉：即一个倾斜穿过窄孔径的光栅似乎是沿着孔径移动的错觉。该模型的核心是，移动由大量具有多种方向和长度的偶极子发出信号。这些偶极子只有在一端受到刺激，然后另一端也受到刺激时才会做出反应。这里报告了旨在检验该模型预测的三个实验。在每种情况下，水平光栅都在孔径上移动，而受试者则注视孔径外的区域。在实验1中，受试者注视在孔径的上方或下方，并报告一组测试点所显示的运动后效（MAE）。正如模型所预测的，离注视点较远的测试点显示出强烈的运动后效。实验2结合了实验1的两种观察条件，以便同时观察注视点上方和下方的测试点。预测得到了证实，因为离注视点较远的测试点比离注视点较近的测试点表现出更强的运动后效。在实验3中，所有条件下的注视点都在孔径下方，并且正如预测的那样，尽管刺激是水平的，但孔径底部附近一个点的运动后效是对角向上的。同样，正如预测的那样，孔径中间一个点的运动后效似乎是水平移动的。最后，预测孔径顶部的一个测试点会看起来对角向下移动，但受试者无法明确报告运动方向，因为运动后效发生在离中央凹太远的地方，无法清晰地看到。总体而言，尽管存在该模型目前无法解释的相关现象，但该模型的预测得到了证实。
