INTRAATTRIBUTE AND INTERATTRIBUTE MOTION INDUCTION

The phenomenon of motion induction occurs, for example, when a bar tha t is presented next to a spot, which itself was presented slightly ear lier, is not correctly perceived to appear everywhere simultaneously, but seems to grow out of the spot. The spot is said to prime one end o f the bar. Experiments have been designed to throw more light on the l ocal and global aspects of this phenomenon, in particular to establish whether this illusory motion percept can be observed when the spot an d the bar stimuli are defined with respect to the background by one of a variety of attributes, such as luminance, color, stereodepth (cross ed and uncrossed), texture, and motion (start and stop). It was found that all attribute combinations supported motion induction readily, bu t that the strength of the perceived motion (as measured by magnitude estimation) varied and depended more on the attribute defining the bar than on the attribute of the spot. Luminance and color gave the most vivid effects, whereas motion and depth showed the least vivid effects . The influence of the amount of luminance and color contrast on the s trength of the effect was also determined and it was found that these variables affected motion induction most at very low contrast levels c lose to detection threshold. It is concluded that the illusory motion in this effect depends only slightly on the particular visual attribut e channel that carries the stimulus information. This is consistent wi th the contention that it is a high-level, attention-related effect, p henomenologically similar to polarized gamma movement.