Pursuit opposite to the vestibulo-ocular reflex (VOR) during sinusoidal stimulation in humans

Pursuit opposite to a simultaneously activated vestibulo-ocular reflex (VOR) was tested during passive sinusoidal body oscillations (0.1-1.0 Hz, amplitudes 10-80 degrees) about the vertical axis in 4 healthy humans, while subjects were asked to pursue a small target moving in phase with the rotating chair with about half its amplitude relative to the head and 1.5 times its amplitude with respect to space. The decrease in gain of the pursuit opposite to the VOR occurred at lower stimulus frequency, stimulus velocity and stimulus acceleration than pure visual pursuit when gain was calculated in relation to target motion in head coordinates. It resembles that of pure pursuit when calculated in relation to target motion in space (earth coordinates, sum of the displacements of the mirror image and of the chair) thus taking the oppositely directed VOR into account. The data fit the assumption of a linear interaction of the VOR (in counterphase) and pursuit.