Induced motion and apparent straight ahead during prolonged stimulation

Induced motion (IM) of a fixation target and the location of the apparent straight ahead (ASA) were measured during and after 2 min of exposure to a moving contoured background. The magnitude of IM increased to an asymptotic level during the exposure period. Following termination of moving contours, illusory motion of the fixation target occurred first in the same direction and then in the direction opposite to that of previous IM. The change in location of ASA followed a similar time course, shifting first in the direction of background motion, reaching an asymptotic position during contour exposure, and then moving in the opposite direction after contour exposure. The similar time courses displayed by IM magnitude change and ASA position change suggest that these two phenomena may be related through a third, causal factor. The hypothesis that IM is caused by motion of ASA is disconfirmed, however, by the fact that IM persists while the ASA is nearly stationary at its asymptotic position.