Correlations between fixation stability and visual motion sensitivity

To assess influences of fixational drift eye movements on motion detection, lower thresholds for motion and drift amplitudes were measured in normal subjects. The threshold was higher without visible surrounds than with a surround, and had a positive correlation with drift amplitude. The same effect, but more pronounced, was found when the surround was visible but flickered synchronously. In contrast, the correlation disappeared in the threshold with a static surround. These results suggest that, while spurious image motions by eye drift can have a detrimental effect, a mechanism tuned for differential motions normally counteracts it.