Eye stabilization by vestibulo-ocular reflex (VOR) and optokinetic reflex (OKR) in macaque monkey: which helps which?

VOR-OKR interaction was studied in macaque monkey in the frequency domain, using various vestibular-visual stimulus combinations in the horizontal plane. At low stimulus frequencies (< 0.1 Hz), the eyes were always stabilized on the optokinetic pattern, irrespective of whether the head, the pattern, or both were rotated. At higher frequencies, the gain of the OKR attenuated, and concomitantly the eyes became increasingly stabilized in space. These findings show that the VOR becomes functionally relevant only at high frequencies. It compensates for the limited bandwidth of the OKR, thereby improving vision provided the pattern to be fixated is stationary in space.