Concurrent manual tracking enhances pursuit eye movements

Abstract

It is known that concurrent manual tracking enhances smooth pursuit of a predictable moving target. Here we examined such facilitation when the target moved unpredictable. In the eye-hand condition, participants were asked to follow a cyan Gaussian target (sigma = 0.6) whose horizontal position was perturbed by the sum of seven harmonically unrelated sinusoids (0.1-2.19 Hz). Simultaneously, they used a mouse to keep the horizontal position of a red Gaussian cursor (8° below) aligned with the target. In the eye-alone condition, the target and cursor motion recorded in the eye-hand condition were replayed, while participants tracked the target only with their eyes. Across 15 participants, baseline RMS eye tracking position error did not differ between the two conditions. However, frequency-response analysis of smooth pursuit eye movement with saccades removed showed that pursuit gain was significantly higher for the eye-hand than the eye alone condition (Cohen’s d=0.62). Consequently, significantly fewer saccade were made in the eye-hand (mean +/-SE: 215+/-6 per 90-s trial) than in the eye-alone condition (250+/-6) while catch-up saccade amplitudes and durations did not differ. We conclude that concurrent manual tracking enhances smooth pursuit, and that this effect is not specific to predictable target movement but is a fundamental property of eye-hand coordination.