THE INVERSION ILLUSION IN PARABOLIC FLIGHT: ITS PROBABLE DEPENDENCE ON OTOLITH FUNCTION.

Observations were made on normal subjects and deaf persons with bilateral labyrinthine defects L-D subjects under three different conditions in parabolic flight 1 free-floating, 2 restrained in a Fiberglas mold, and 3 standing on the overhead during a motified parabola generating about -0.05 G unit. There were interindividual differences in the reactions among the normal but not among the L-D subjects. Some normal but none of the L-D subjects experienced a reversal of their personal orientation with regard to up-down under all three conditions. This reversal was considered to have its genesis in the vestibular organs, probably the otolith apparatus. Our findings are in accord with Russian reports describing feelings of inversion among cosmonauts in orbital flight. Attention is called to the necessity of distinguishing between information furnished by touch-pressure, kinesthesis, and stereagnosis under ordinary conditions and agravic touch-pressure, agravic kinethesis, and agravic steragnosis. Author