Effects of full-field visual input on the three-dimensional properties of the human vestibuloocular reflex

The three-dimensional (3-D) properties if the vestibuloocular reflex (VOR) were studied in six normal human subjects during passive whole-body rotations in darkness and with full-field visual input in light. Subjects were asked to fixate a point target stationary in space straight ahead or to imagine such a target in darkness. Using a 3-D rotating chair, subjects were rotated sinusoidally (frequency .3 Hz, maximum speed 37.5 degrees/s) about an earth-vertical axis for horizontal stimulation and about an earth-horizontal axis for vertical and torsional stimulation. The subject faced forward for vertical stimulation, 90 degrees to the side for torsional stimulation, or 15 degrees to the right or left side for combined vertical and torsional stimulation. Left eye position was measured using 3-D search coils. The VOR response was quantified using the 3-D analogue of gain, a 3 x 3 matrix where each element describes the dependence of one component--torsional, vertical, or horizontal--of eye velocity on one component of head velocity. Average gain matrices were calculated for three cycles of rotation (10 s). Major findings were: (1) Gain values for the VOR were higher in light than in darkness for all directions. In light, vertical and horizontal responses were fully compensatory in both magnitude and direction, whereas the torsional responses were still weak. (2) Intersubject variability, large in the dark, was very small in the light for the vertical and horizontal responses but still considerable for the torsional.(ABSTRACT TRUNCATED AT 250 WORDS)