FREQUENCY SPECIFICITY IN THE ADAPTATION OF APPARENT CONCOMITANT MOTION

The apparent motion of a fixated spot stimulus during head oscillations (apparent concomitant motion, ACM) was measured before and after an adaptation period during which the fixation stimulus moved in synchrony with the head. During the adaptation period, the fixation stimulus moved either in the same (with) or the opposite (against) direction as did head movement. With adaptation increased ACM in the direction opposite head motion, whereas against adaptation increased ACM in the same direction as head motion. Pre- and postadaptation measures were obtained for.25-,.5-, 1.0-, and 2.0-Hz active head movements. Each of these frequencies was used in separate sessions as the adaptation frequency. ACM changes were greatest when the test and adaptation frequencies were the same, demonstrating frequency specificity of ACM adaptation. This frequency specificity, which is similar to that of the vestibulo-ocular reflex, indicates that ACM adaptation may reflect plasticity in oculomotor systems.