Pursuit Gain is Not Affected by Saccadic Adaptation

Abstract

Abstract: : Purpose: The increase in catch up saccade amplitude during pursuit adaptation has been interpreted as resulting from the adaptation of saccades.¹ If pursuit adaptation is capable of affecting saccades, a plausible corollary would be that adaptation of saccades could affect the gain of the pursuit. The purpose of this experiment was to test this hypothesis by looking at the effects of saccadic adaptation on pursuit gain. Methods: Five subjects participated in the experiment. Eye movements were recorded at 120Hz using a video based eye tracker (ELMAR 2020). Two trials of initial pursuit responses were measured in response to rightward and leftward step ramp targets with ramp velocities of 5, 10 and 20 degrees/sec. Following this, baseline saccade responses (100 trials) were measured. Then saccadic adaptation was produced with a gain decreasing paradigm, induced by displacing the stimulus backwards by 3 degrees from the initial target step (12 deg) for 1000 trials. The displacement of the stimulus occurred once the saccade velocity reached 40 degree/sec. Following the saccadic adaptation, the pursuit response was measured again in response to the same step ramp targets. The magnitude of saccadic adaptation for each subject was calculated as the change in saccadic gain as a function of the intrasaccadic step (difference between the saccadic gain at baseline and gain for the last 100 trials of saccadic adaptation phase). The pursuit gains were then calculated for each ramp velocity for both the pre and post adaptation trials and were compared using repeated measures ANOVA. A linear regression analysis was also performed to calculate whether the magnitude of saccadic adaptation had an effect on the mean difference in pursuit gain. Results: A significant amount of saccadic adaptation was induced in all the five subjects (p < 0.01). There was no significant change in pursuit gains for any velocity and the mean difference in pursuit gains were unaffected by the magnitude of saccadic adaptation (p > 0.05). Conclusions: Saccadic adaptation does not affect pursuit gain indicating that saccadic recalibration which is known to be direction and amplitude specific is also system specific and does not transfer to the pursuit system. 1. Nagao, S., Kitazawa, H., 1998. Neurosci. Res. 32, 157–169.

Keywords: eye movements: saccades and pursuits • plasticity • eye movements