Individual differences in the asymmetry of binocular saccades, analysed with mixed-effects models

We analysed the reliability of individual differences in parameters of binocular saccadic eye movements. During saccades between isovergent targets, the movement of the right and left eye are not exactly symmetrical (conjugate). Typically, the abducting eye has a shorter latency and reaches a higher velocity, so that a transient divergence occurs during the saccade. For the asymmetry in latency and for the maximum of transient divergence, we applied statistical mixed-effects models in a repeated-measures design with 39 subjects and found that the variability between subjects was much larger than the variability from Sessions 1 to 2 (about 8 days later). The retest correlations were 0.54 for the latency difference, and 0.82 for the transient divergence maximum. We conclude that significant individual differences exist in the asymmetry of binocular saccades and that these can be observed with about 20 saccadic trials per subject.