Head-free pursuit of pseudo-random target motion

Experiments have been conducted in which subjects were required to pursue a target moving in the horizontal plane with co-ordinated movements of the head and eyes. Target motion was pseudo-random in form, composed of four sinusoids. The three lower frequencies of the stimulus were maintained at 0.11, 0.24 and 0.37 Hz with a peak velocity of 10 degrees/s, whilst the frequency and velocity of the highest frequency component (F4) were varied. When all frequencies were below 0.4 Hz, eye movements were smooth and gaze velocity gain was high (0.95), but when F4 was increased up to 1.56 Hz or when the velocity of F4 was increased up to 40 degrees/s, gaze velocity gain decreased significantly. When voluntary head movements were countered by whole-body rotation to eliminate the input to the semicircular canals, gaze velocity gain increased because there was no longer any requirement to suppress the vestibulo-ocular response to head rotation. The results are in accord with those of previous experiments involving head-fixed pursuit and vestibulo-ocular suppression.