Adaptive gain control of saccadic eye movements

Properties of gain adaptivity in the saccadic system were studied. Subjects had to track a target which moved in single or double steps. The first target step which elicited the primary saccade had an amplitude in the range of 8-16 deg. The primary saccade triggered a further target displacement of 4 deg either in the same or--in different experimental sessions--in the opposite direction of the first target step. These consistent intrasaccadic target displacements lead to adaptive changes of saccadic amplitudes. The experimental data show that the saccadic system adapts to the stimulus sequence in a simple, parametric manner, namely by changing its gain. Consequently, it is assumed that a single gain element determines saccade sizes for all target eccentricities. Further, it is shown that adaptation has different time courses for gain increase and decrease, and its performance is close to completeness. The results are discussed with respect to the undershooting behaviour of goal-directed saccades and the functional demands to the saccadic system.