Tiny eye movements, such as micro-saccades, ocular tremor, and drifts, occur involuntarily during fixation. We found evidence that involvement of body action and anticipation of visual stimuli modulates them.
While eye movements were monitored, subjects performed the working memory task with a touch-screen display in two different conditions. In the passive condition, each number was shown for 400-ms and spaced in time by 500-ms automatically. In the active condition, touching action was required to trigger the appearance of each number. The delay between the touch and stimulus onset was constant within a block as 200, 500, or 800-ms. Subjects were prompted to type in the number sequence after five numbers were shown.
As a measure of fixation instability, deviation of eye position was analyzed by comparing eye positions with those during the reference interval (0~50ms time period after the number onset). We observed two results: first, the deviation was smaller in pre-reference time than in post-reference time. Second, the deviation was smaller in the active condition. These results show that micro eye movements are influenced by attentive anticipation of upcoming events, which becomes more pronounced with bodily interactions. These findings suggest a cross-modal interaction among visual, motor, and oculomotor systems.