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 coi l system. Saccadic adaptation was induced artificially by dislocating the target (by about 30% of the initial step) either forward (gain inc rease) or backward (gain decrease) during the primary saccade (''doubl e-step paradigm''). Duration, peak velocity and peak acceleration and deceleration of a ''standard 12 deg saccade'' were computed from the d ata and were compared for the conditions of gain decrease, gain increa se and the control without gain adaptation, The gain as well as the pe ak velocity and duration of the saccades showed an increased variabili ty during the adaptation, In general, the abducting saccades had a hig her peak acceleration than the adducting saccades, and all subjects sh owed an idiosyncratic pattern of the acceleration and deceleration, In the gain increase paradigm the subjects showed an increase in the dur ation and a decrease in the peak velocity. In the gain decrease paradi gm there was a significant smaller ratio of peak acceleration/peak dec eleration compared to the gain increase and the control condition. The findings demonstrate that rapid gain adaptation influences the dynami cs of saccades in a specific way: peak saccadic velocity decreases and duration increases in the gain increase paradigm and peak acceleratio n/peak deceleration decreases in the gain decrease paradigm, Moreover, these results also suggest that the deceleration is neuronally contro lled and not merely a result of mechanical constraints.