Perceptual and eye movement responses elicited by linear acceleration following spaceflight.

Responses of four crewmembers were measured before and after a 9-d Spacelab Mission during inter-aural (y-axis) and longitudinal (z-axis) linear acceleration. During one test, eye movements were recorded with simultaneous sinusoidal acceleration and constant-velocity optokinetic stimulation. Postflight responses indicated changes in the horizontal sinusoidal response during the y-axis trials. In another test, subjects indicated direction of acceleration during a series of low acceleration steps. More incorrect direction indications were observed postflight, and the y-axis sensitivity increased while the z-axis sensitivity decreased for three subjects. In a third test, subjects used a joystick to null pseudo-random linear motion. Not one subject showed a significantly enhanced ability to null linear motion in the y-axis, while two subjects showed an enhanced ability during z-axis testing postflight. Oculomotor and perceptual responses to linear acceleration are modified by exposure to microgravity and become more variable postflight. The observed changes may be due to an altered interpretation of inertial cues in space that is inappropriate postflight.