The effect of induced movement and the Roelofs phenomenon on human localization

MacDonald, Edward Hugh (1982) The effect of induced movement and the Roelofs phenomenon on human localization. Masters thesis, Memorial University of Newfoundland.

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Abstract

Induced movement is the perceived movement of a stationary object in the direction opposite to that of an objectively moving background. Six experiments were conducted to determine if the induction effect could be explained strictly in terms of the object-relative movement between the visual target and its background, or whether the moving background changes the egocentric coordinates of the observer such that the perceived target motion arises from the change in its position relative to the shifting egocentric or subject-relative axes. Subjects pointed to a target light located in their objective median plane (1) in the absence of any other stimulus in the visual field, (2) in the presence of an offset stationary fluorescent frame, (3) while the frame was moving leftward or rightward, and (4) after exposure to identical frame motion occurring immediately prior to the onset of the target light. The results showed that pointing errors with respect to the control readings were smallest with the stationary frame, somewhat larger after frame motion in the absence of the light, and largest during frame motion in the presence of the light (induced motion). In the induced movement condition, the direction of motion affected both the direction and size of subsequent pointing errors. In contrast, the stationary frame in the presence of the light or frame motion in the absence of the light affected the size but not the direction of subsequent errors. It is argued that both subject-relative and object-relative factors are involved in the perception of induced movement and an alternative interpretation is suggested which incorporates both of these elements. Finally, an argument is made for the importance of stimulus size as a parameter in induced movement.

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