Abstract
Power and Moulden have proposed a model which accounts for the movement of gratings in apertures including the barber pole illusion. It predicts the direction of motion aftereffects which follow from perceived veridical motion and the direction of these aftereffects which follow from the illusory movement experienced during the barber pole illusion. At a perceptual level, the model predicts motion aftereffects will follow direction of apparent movement rather than veridical direction. Four experiments tested this prediction. In Exp. 1 a spiral was viewed under flickering light so it appeared to be moving in the direction opposite to true motion, and the aftereffect was opposite to the apparent direction. In Exp. 2 the spiral was viewed through a narrow aperture so that it was effectively a grating appearing to move in the opposite direction to veridical motion. Again, the motion aftereffect was opposite to the apparent rather than true direction of rotation. In Exp. 3 a sectored disc was used, and similar results were obtained. In Exp. 4 the sectored disc was videotaped so that it appeared to be rotating in the direction opposite to true motion. The after motion to this “wagon wheel” effect was opposite to its apparent direction of rotation on the screen. In all experiments the predictions were confirmed, thereby confirming the general principle that motion aftereffecrs follow apparent rather than real direction of movemenr.