Influence of predictability on saccade timing in a head impulse VOR suppression task.

Gaze stabilization performance has been shown to be influenced differently when the head is either passively or actively moved in normal healthy participants. However, for a visual fixation suppression task, it remains unknown if the pattern of coordinated head and eye movement is influenced differently by passive or active head movements. We used a suppression head impulse paradigm (SHIMP), where the subject's goal was to maintain gaze stabilized on a visual target that moved with the head during rapid impulsive head movements, to evaluate gaze fixation performance in three conditions: (1) passive-unpredictable where the examiner applied impulsive head yaw rotations with random timing and direction, (2) passive-predictable where the direction of head rotation was announced and then the examiner repeatedly applied impulses in the same direction, and (3) active where the test subject self-generated their head movements. Thirteen young healthy adults performed all three conditions to assess the percentage of early saccades that initiated the gaze shift toward the final visual target position and the latency of first saccades. Early saccades were defined as those occurring within the duration of the head impulse. Results showed that active head impulses generated the greatest percentage of early saccades, followed by predictable and unpredictable. Among the two passive conditions, predictability shortened the first saccade onset latencies. Active condition onset latencies were shorter than in either of the passive conditions, showing a consistent head-leads-eye pattern defining a specific behavioral pattern that could vary across patient groups leading to insights into central neural mechanisms that control eye-head coordination.