OTOLITH RESPONSES IN MAN DURING PARABOLIC FLIGHT

The influence of the varying gravito-inertial (G(z)) force during para bolic flight on human otolith function was investigated experimentally . It was hypothesised that a varying G(z) force profile initiates an o tolith-ocular response that manifests itself in modulation of optokine tic nystagmus slow-phase eye velocity (OKN-SPV). Six subjects were sea ted in the ESA-Caravelle, facing perpendicular to the aircraft's longi tudinal axis. The G(z) profile was subsequently 1.8 G(z) pull-up, 0 G( z) microgravity, and 1.8 G(z) recovery, each phase lasting about 20 s. Vertical eye movements were recorded with electro-nystagmography thro ughout the parabolic manoeuvre. Conditions were: (1) visual fixation, (2) darkness and (3) optokinetic stimulation of 50 deg/s in an upward or downward direction, projected on a cylindrical screen at 0.6 m view ing distance. No consistent nystagmus or gaze shift was measured in da rkness. With optokinetic stimulation, however, ANOVA revealed downward enhancement of OKN-SPV by 5-degrees/s in 1.8 G. hypergravity, as comp ared with the 0 G(z) condition and the 1 G(z) condition. It is conclud ed that an otolith-ocular pathway modulates optokinetic eye movements in parabolic flight.