Otolith Responses During Centrifugation Along Three Axes of Orientation

摘要

Humans perceive tilt by the otoliths as a result of shear forces on the maculae. The current study was designed to investigate the influence of forces from different directions on eye movements and tilt perception. The study was composed of experiments in a human centrifuge. In the first experiment, ocular torsion and experienced tilt due to centrifugal stimulation were assessed, with a maximum of 1.5 G acceleration along the X-, Y- and Z-axes. In the second experiment, the subjects' estimation of tilt was recorded during +1.0 G and -1.0 G centrifugal stimulation along the three axes of the body, with and without visual reference. Results of an earlier study suggested that the utriculus generates conjugate torsional eye movements, and the sacculus generates disjunctive torsional eye movements. This hypothesis found support in the present investigation when the behavior of the two eyes was determined simultaneously. A persistent underestimation of the subjects' tilt perception was registered during stimulation with centrifugal forces less than or equal 1.0 G. This underestimation of tilt appeared least during stimulation along the longitudinal axis (Z, gain: 0.87), and was more prominent during stimulation along the X- and Y-axes (gain: 0.56 and 0.60, respectively). The underestimation occurred even though a calibration procedure was used to control for the possible inadequacy of subjects to adjust intended angles by joy-stick indication. This procedure would exclude such a sensorimotor factor as a cause for the underestimation.