Abstract
Purpose: In daily life, visual tasks from fixating and pursuit to search and discriminations, often have to be performed while the observer is in motion rather than immobile. Locomotion, however, induces various head movements (HM), which displace the eye and need to be compensated for in order for the eye to be directed appropriately. Here we studied the effects of locomotion on the accuracy of eye position during fixation and linear pursuit of moving spots. Methods: Observers were standing, walking or running on a treadmill. Translational and rotational HM (pitch, bob, yaw, heave) were measured with an OptiTrack motion capture system, and eye position was recorded with an EyeLink eye tracker, while observers attempted to keep their eyes on a stationary or horizontally or vertically oscillating spot with different amplitude and velocity. Results: Pitch and yaw angles remained constant for all pursuit movements when observers were standing, while these angles varied systematically with locomotion, especially for walking. Bob-pitch, and heave-yaw movements were correlated in most visual conditions, such as to compensate for each other's deviations. When comparing the influence of visual stimulus amplitude or velocity on pitch and yaw movements, standing and running gave fairly similar results, while walking resulted in increased downward pitch. Conclusion: While both kinds of locomotion introduced more pursuit errors and more variability, running was in many ways less disruptive than walking, providing some evidence for the contention that in the case of running, compensation for HM is especially well adapted (Bramble & Lieberman, 2004).