ESM Antisaccade Performance Figure 6. Relationship between prosaccade (PS) and antisaccade (AS) performance. A. Median prosaccade latency and AS directional error rate. B. Percentage of express saccades in the PS task and AS directional error rate. C. Median PS latency and median AS prosaccade error latency. D. Percentage of express saccades in the PS task and median AS error prosaccade latency (AS). E. Percentage of express saccades in the PS task and percentage of ES in AS prosaccade errors. F. The difference between correct AS latency and PS latency calculated for each subject, and AS directional error rate. On each plot the solid black line is the least-squares linear regression line calculated for the whole dataset. Data from ESMs: grey symbols; data from normal subjects: black symbols. doi:10.1371/journal.pone.0047688.g006 various relationships have been examined, the correlations, while statistically significant, were relatively weak [33,34]. The highest correlation coefficient was for the relationship between the percentage of express saccades in prosaccade tasks and pro- saccade errors in the antisaccade task. This is consistent with the hypothesis that pro-saccade errors in the antisaccade task are uninhibited reflexive responses to the target. ESMs were relatively unsuccessful at inhibiting reflexive responses (hence the higher directional error rate), but as will be discussed below this could be a consequence of the low latency nature of their reflexive responses. A number of models have been developed which seek to explain patterns of saccade latency. Accumulator models describe saccade triggering in terms of a decision signal rising from a baseline to a threshold; when the threshold is crossed, a saccade is initiated [35]. Saccade latency modulations are related to changes in the baseline level of activity, the rate of rise of the decision signal or the level of the threshold [36]. For antisaccades, competitive race accumulator models [37] assume that a prosaccade decision signal (initiated by the appearance of the target, and therefore exogenously triggered) and an antisaccade decision signal (gener- ated internally and therefore usually considered to be endogenous) ‘‘race’’ each other towards threshold. If the prosaccade signal ‘‘wins’’, a prosaccade error is the result; if the antisaccade signal ‘‘wins’’, a correct antisaccade is the result. On this account it is the inability of ESMs to successfully inhibit low latency prosaccades (many in the express latency range) that explains their perfor- mance in antisaccade tasks (higher error rates, lower prosaccade PLOS ONE | www.plosone.org 6 October 2012 | Volume 7 | Issue 10 | e47688