[Orientation illusions in weightlessness].

Results of the ANKETA and OPROSNIK experiments performed by 102 cosmonauts in and post flight were analysed. It is shown that perceptive disturbances (orientation illusions) developed in the period of early adaptation to weightlessness were not an inherent feature of individual persons but regular responses of the body sensory systems. The character, intensity, duration, and the dynamics of illusion responses in space mission are described. Forms of the vestibular disorders, types of adaptation of the sensory systems and classification of spontaneous illusion responses in the weightless environment are presented. Hypothesis for possible mechanisms of the illusion responses in weightlessness is suggested.