Ground based eccentric chair experiments.

Two subjects were rotated eccentrically in a manner described before. In contrast to a normal control group settings of a luminous line to the subjective vertical were almost unrelated to the gravitoinertial summation vector of gravity and centrifugal forces about four weeks before and totally so shortly after space flight. Only after four days post flight had passed a noticeable relation to the gravitoinertial vector re-established itself in the one subject which actually flew. The correspondence became normal six days after flight. Since there were no clinical abnormalities evident in the subjects, it is suggested, that both subjects suppressed their vestibular information presumably as an effect of vestibular deconditioning training before flight. In addition as a consequence of the flight experience one subject continued to ignore it several days after the flight.

Ocular torsion during microgravity on a space mission in 1992.

On a space mission in 1992 we investigated the effect of pure neck receptor stimulation on eye roll position in space. To do this, we used the flash afterimage method. We found that eye rotations in static tilted head positions are absent in weightlessness. This suggests that in microgravity the neck position receptors do not contribute to a measurable extent to static OCR.

Oculovestibular interactions under microgravity.

On a space mission in March 1992 a set of experiments were performed aimed at clarifying the interaction between visual, proprioceptive and vestibular inputs to the equilibrium system. Using the VESTA goggle facility from the European Space Agency we investigated the effect of pure neck receptor stimulation on eye position as measured by the flash afterimage method and on perception of a head-fixed luminous line in space. Space vestibular adaptation processes were measured by rotating pattern perception during prescribed head movements. It was found that static ocular counterrotation does not occur under microgravity conditions. This result suggests that the neck receptors apparently do not contribute to a measurable extent. The subjective orientation of a vertical line was perceived correctly inflight. Obviously neck receptors on the perception level can fully substitute for the ineffective equilibrium organs of the inner ear within less than 4 days. The rotating pattern perception during different head motion patterns is not influenced by the absence of a gravity reference.

Responses to eccentric rotation in two space-bound subjects.

Two subjects were rotated eccentrically in the manner described previously. In contrast to a normal control group, settings of a luminous line to the subjective vertical were almost unrelated to the gravitoinertial vector before, and totally so shortly after, space flight. Only 3 days postflight did a clear relation to the gravitoinertial vector re-establish itself in the one subject who actually flew. The correspondence became normal 5 days after the flight. Since there were no clinical abnormalities evident in the subjects, it is suggested that both subjects suppressed their vestibular information, presumably as an effect of vestibular deconditioning training before the flight. In addition, as a consequence of the flight experience one subject continued to ignore it several days after the flight.

Clinical verification of a unilateral otolith test.

In a previous study we reported promising results for a new test to differentiate in vivo unilateral otolith functions. That study pointed to a need for further validation on known pathological cases. In this presentation we will detail the results gathered on a group of clinically verified vestibular defectives (verum) and a normal (control) group. The subjects in the verum group were former patients of the ENT clinic of the university hospital. These subjects had usually suffered from neurinoma of the VIIth cranial nerve or inner ear infections. All had reguired surgical intervention including removal of the vestibular system. The patients were contacted usually two or more years postoperatively. A group of students from the pre- and clinical phase of medical training served as control. Both groups were subjected to standardized clinical tests. These tests served to reconfirm the intra- or postoperative diagnosis of unilateral vestibular loss in the verum group. In the control group they had to establish the normalcy of the responses of the vestibular system. Both groups then underwent testing on our eccentric rotary chain in the manner described before. Preliminary results of the trials indicate that this test may indeed for the first time offer a chance to look at isolated otolith apparati in vivo.

Parabolic flight as a tool to measure ocular counterrotation in a reduced force environment.

Five unmedicated subjects were flown in parabolic flight. The aircraft, a Caravelle, performed single parabolae every 2 to four minutes. This resulted in alternating phases of normal, hyper-, hypo- and again hyper-gravity. Subjects sat yoga fashion upright facing towards the aircraft cockpit. Head and/or trunk were deflected 30 degrees from the upright, stimulating otolith and/or neck receptors. During each pullup, low-g phase and pullout of the parabolae a picture of the left eye was recorded on video tape. On the ground ocular roll (OCR) was determined from these video recordings. OCR ranged from 0.9 to 6.9 degrees in l-g and from 1 to 7.2 degrees under high-g, depending on head and trunk position. Neck receptor contribution was found to induce OCR of 0.2 degree to 2.1 degrees in two subjects.

Subjective luminous line perception under changing g-load and body-positions in parabolic flight.

Five healthy subjects were subjected to parabolic flight with laterally tilted head, trunk, or body position. A vertical luminous line was viewed by the subjects in a head-fixed goggle device. During normal, hyper- and hypogravity phases subjective luminous line orientation was measured. The data imply that stimulation of the neck position receptors markedly influences the perception of the subjective vertical as well as mechanisms of convergence of otolithic signals and visual information within the brain.