Oculomotor inhibitory control in express saccade makers.

Express saccade makers (ESMs) produce high proportions (>30 %) of low-latency (80-130 ms) express saccades in tasks in which such responses are usually suppressed. In addition, high directional error rates on the antisaccade (AS) task suggest a failure of oculomotor inhibitory mechanisms in ESMs. However, the AS task is complex and does not provide a measure of inhibitory processes in isolation. We therefore examined inhibitory control in 25 ESM and 28 non-ESM ('Norm') participants, using a minimally delayed oculomotor response (MDOR) task. After a randomised fixation period, a pro-saccade target appeared for 200 or 1,000 ms. Participants were instructed to maintain fixation and saccade to the target position upon target offset. In a control task, they saccaded on target onset. Overall, saccade latency was considerably increased in the MDOR task compared to the control task (354 vs. 170 ms; p < 0.001), and we also observed a latency modulation with display time (200: 399, 1,000: 302 ms; p < 0.001). However, there was no evidence of a difference between groups (p = 0.29). Errors consisted primarily of responses to target onsets and error rates were comparable between the groups (p = 0.33). The overproduction of fast, reflexive responses was still observed in ESMs who generated a higher proportion of their errors within the express latency range (p < 0.001). We confirmed that in the AS task, the ESMs exhibited a higher directional error rate (p = 0.03). These results suggest that the performance 'deficit' observed on the AS task in ESMs cannot be attributed to generally weaker inhibitory control.