Short term modification of disparity vergence eye movements

Dynamics of disparity vergence eye movements can be modified by adaptive stimuli that generate large transient disparities. These modifications were observed for convergence as well as divergence eye movements. After modification, the peak velocities of the step responses for convergence and divergence were substantially higher than in normal baseline responses, a change observed in all four subjects studied. The change in peak velocity of a step response occurred very rapidly after presentation of the adaptive stimuli. Main sequence plots showed that first-order dynamic characteristics increased for post-adaptive responses with respect to normal step responses. Hence, response modification could be quantified as a change in gain accompanied with an increase in the effective response time constant. The adaptive responses to convergent and divergent ‘disappearing’ step stimuli revealed that the adaptation process modifies the high-velocity component of both disparity convergence and divergence eye movements. Moreover, a gain change in this component alone could account for both the gain and the time constant modifications seen in the overall response. A process of recovery or de-adaptation was also observed for both convergence and divergence eye movements. This observed short-term modification demonstrates a unique control mechanism for vergence eye movements that is effective in either direction.