Rapid gain adaptation affects the dynamics of saccadic eye movements in humans.

The effect of rapid gain adaptation on the dynamics of visually guided saccades was investigated in six human subjects by using a search coil system. Saccadic adaptation was induced artificially by dislocating the target (by about 30% of the initial step) either forward (gain increase) or backward (gain decrease) during the primary saccade ("double-step paradigm"). Duration, peak velocity and peak acceleration and deceleration of a "standard 12 deg saccade" were computed from the data and were compared for the conditions of gain decrease, gain increase and the control without gain adaptation. The gain as well as the peak velocity and duration of the saccades showed an increased variability during the adaptation. In general, the abducting saccades had a higher peak acceleration than the adducting saccades, and all subjects showed an idiosyncratic pattern of the acceleration and deceleration. In the gain increase paradigm the subjects showed an increase in the duration and a decrease in the peak velocity. In the gain decrease paradigm there was a significant smaller ratio of peak acceleration/peak deceleration compared to the gain increase and the control condition. The findings demonstrate that rapid gain adaptation influences the dynamics of saccades in a specific way: peak saccadic velocity decreases and duration increases in the gain increase paradigm and peak acceleration/peak deceleration decreases in the gain decrease paradigm. Moreover, these results also suggest that the deceleration is neuronally controlled and not merely a result of mechanical constraints.