The vestibular apparatus is the nonauditory portion of the inner ear that mediates the subjective sensation of motion and spatial orientation of the head, adjusts muscular activity and body position to maintain posture, and stabilizes in space the fixation point of the eyes when the head moves, in order to provide a stable image upon the retina. The functioning of the vestibular system is often checked clinically by means of the caloric test, in which the head is tilted backward by about 60 degrees and either warm or cold water is introduced into the external auditory meatus on one side. The immediate results are usually vertigo, nausea, nystagmus, and twisting of the head and body.

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