Some vestibular problems related to orientation in space.

Aircraft and spacecraft introduce unnatural combinations of vestibular and visual stimuli. Many of these situations produce spatial disorienta-tion and performance degradation which can be anticipated by knowledge of the mechanics of vestibular stimulation. Experiments to test predictability of reactions to unnatural vestibular stimuli have contributed to current knowledge of vestibular function. Some of these experiments are reviewed to illustrate methods employed for the assessment of vestibular function and to illustrate implications of the results for spatial orientation and theory of vestibular function.