European vestibular experiments on the Spacelab-1 mission: 6. Yaw axis vestibulo-ocular reflex.

In two Spacelab-1 crew members the lateral eye movements evoked by active angular oscillation of the head in yaw at 1 Hz were recorded in-flight and post-flight. In one, the responses to passive angular oscillation in yaw at 0.2-1 Hz were also studied pre- and post-flight. In the absence of visual fixation there was no significant change in the gain of either the active or passive vestibulo-ocular reflex (VOR) attributable to exposure to microgravity. However, when the subject fixated on a visual target that moved with his head the suppressed VOR gain was lower on the first post-flight test (performed 16 h after landing) than that obtained pre-flight or on subsequent post-flight tests.