Adaptive changes in dynamic properties of human disparity-induced vergence

PURPOSE. Vergence eye movements undergo adaptive recalibration in response to a training stimulus in which the initial disparity is changed just after vergence begins (the double-step paradigm). In the present study the chang es in the dynamic properties of convergence, speed and acceleration, were e xamined by using this double-step paradigm, before and after adaptation. METHODS. Four normal subjects participated. Three-dimensional visual stimul i were provided by a head-mounted display with two liquid crystal diode (LC D) panels. To induce adaptation, a double step of disparity was used: an in itial step from distances of 2 to I m was followed by a second step to dist ances of 0.7 m ("increasing paradigm") or 1.4 m ("decreasing paradigm") aft er a constant period of 0.2 seconds. The dynamic properties of vergence wer e compared before and after 30 minutes of training with these paradigms. RESULTS. Peak velocity of convergence became significantly greater (increas ing paradigm) or smaller (decreasing paradigm) after 30 minutes' training. Changes in the dynamic properties of convergence were also obvious in phase -plane (velocity versus position) and main sequence (peak velocity versus a mplitude) plots. Further analysis revealed that adaptive increases in verge nce velocity were accomplished by an increase in the duration of the accele ration period, whereas adaptive decreases were induced by a decrease in the maximum value of acceleration CONCLUSIONS. The pattern of change in the dynamic characteristics of vergen ce after adaptation was similar to that of saccades and the initiation of p ursuit eye movements, suggesting common neural mechanisms for adaptive chan ges in the open-loop control of eye movements.