The relationship between vestibulo-ocular reflex plasticity and changes in apparent concomitant motion

The vestibulo-ocular reflex (VOR) and the apparent motion of a spot stimulus fixated during head movement (apparent concomitant motion, ACM) were measured before and after an adaptation period during which subjects attempted fixation of a stimulus which moved either in the same or opposite direction as head oscillations. Movements of the head were voluntary and paced by a metronome at either 0.5 or 2.0 Hz during the 4 min adaptation period. Pre- and post-adaptation measures of VOR and ACM were obtained for both frequencies of head oscillation. VOR and ACM were altered similarly by the period of exposure to correlated head and stimulus motion. Viewing a stimulus moving in the same direction as head motion resulted in decreased VOR gain and increased ACM in the opposite direction as head motion. Viewing a stimulus moving opposite head motion resulted in increased VOR gain and increased ACM in the same direction as head movement. Differences between pre- and post-measures tended to be maximal at the adaptation frequency, but transferred to a lesser degree to the other frequency. The results indicate that changes in motor and perceptual systems are related, and are consistent with the proposal that VOR gain is a determinant of ACM.