Induced motion and the visual vertical: effects of frame size

Induced visual motion and the rod-and-frame effect have both been explained in terms of changes in the observer's spatial orientation. Accordingly, we examined the effects of large and small visual frames on the two phenomena in the present experiment, testing 8 male and 8 female undergraduates. During induced motion, subjects noted the perceived motion of a stationary central point of light and then moved this light back to its apparent original location. For the visual vertical, subjects aligned two points of light to indicate the perceived vertical in the presence of straight and tilted frames. As predicted, the larger frames generated more induced motion and greater displacement of the visual vertical. These results may have occurred because the larger frame had a greater effect on the subjects' spatial orientation, perhaps due to the more extensive involvement of the peripheral, or ambient, visual system.