Adaptation of initial smooth-pursuit eye velocity in humans

The effect of learning on smooth-pursuit eye movements was examined in six healthy subjects by presenting a sequence of horizontal step-ramp target motions that started with a target velocity of 10 degrees/s or 20 degrees/S for 100 ms and then in one direction changed to a second target speed that was twice as fast (learning direction). Direction, velocity, duration, and time interval between the ramps changed randomly during the entire experiment. For the learning direction, the velocity of eye movements in the interval 50-80 ms after the onset of pursuit increased with the number of performed trials. In the second direction, the target velocity of 10 degrees/s and 20 degrees/s stayed constant during the ramp (control direction). In contrast to the learning direction, the eye velocity did not change during the session in most of the tested subjects. The initial smooth-pursuit eye velocity increased in the learning direction after about 60-80 learning trials. There was no generalization of the velocity increase to the control direction, and there was no change in the smooth-pursuit onset latency for the control or for the learning direction during the experiment. The results suggest that learning influences smooth-pursuit onset even when a complex paradigm with two different target velocities is used.