Saccadic Adaptation with an Adapted Visual Error

To enable the visual system to accurately gather information about the environment in spite of appearing changes in the oculomotor plant saccadic eye movements are continuously adjusted by the brain. If the saccadic target is systematically shifted inward or outward during the saccade for a few tens of trials, the amplitude becomes shorter or longer, respectively. The error signal that mainly drives the saccadic adaptation is the distance of the expected target position to the actual target position after the saccade with respect to the fovea. An open question is the nature of the adaptation process. One possibility is that the motor command which drives the saccade to the presented target is adjusted. The other possibility is a changed perception of the target location. In our study subjects performed rightward saccades of 12 deg amplitude and we presented a constant error of 3 deg to the left of the eye’s landing position at the end of each adaptation trial. Beforehand, leftward saccades of 3 deg amplitude, i.e. of the same size as the induced visual error, had been adapted in the same session. If saccadic adaptation is achieved via motor adjustment, there should be no effect of the adaptation of the small saccade on the adaptation course of the large saccade. On the other hand if the adaptation of the small saccade is achieved due to a visual remapping of the target, the change of perceived target location should have a modifying influence on the adaptation of the large saccade. We found a clear effect of the adaptation state of the small saccade on the adaptation course of the large saccade. The results suggest that the saccade amplitude is adapted via an adjustment of target position. Meeting abstract presented at VSS 2012