An adaptive control model for human head and eye movements while walking

When a person walks the head undergoes horizontal and vertical rotations, and also horizontal and vertical translations. To visually fixate on an object while walking, compensatory horizontal and vertical eye movements must be made. The model for this gaze (head plus eye) control system includes three types of eye movements: smooth pursuit, saccadic, and vestibulo-ocular. The smooth pursuit system uses a target-selective adaptive controller that compensates for the large inherent time delay and produces zero-latency tracking of predictable targets. Target movements were selected to minimize the role of the saccadic control system. Typical tracking is shown while seated with the head restrained, standing with unrestrained head, performing voluntary head rotations, and walking. Each additional degree of freedom produced additional head movements that were compensated by additional eye movements. It is shown that while a human walks the effects of head rotations (yaw) cancel the effects of head translations, thus minimizing the resulting horizontal eye rotations necessary to maintain fixation.