Subjective postural vertical in peripheral and central vestibular disorders.

The perception of subjective postural vertical was assessed in normals and patients with peripheral and central vestibular disorders and spasmodic torticollis. The subjects were seated in a motorized gimbal with the head and torso restrained and their eyes closed. The gimbal executed 7-10 cycles of tilt around the vertical at 1.5 degrees/s in either pitch or roll. Subjects indicated when they began to feel upright and again when they began to feel tilted by an analogous 3-position joystick. Normal subjects felt upright within a sector of 5-6 degrees around vertical in pitch and roll. Five patients with absent vestibular function, 25 torticollis patients and 3 patients with acute unilateral peripheral vestibular lesions showed a significant increase of the sector in pitch and roll, but only the latter had a mild directional bias. Two patients with long standing complete unilateral vestibular deficit and 8 patients with up or downbeat nystagmus in the vicinity of upright had abnormally large sectors within which they felt to be upright. The results suggest that vestibular function is important for the accurate perception of the postural vertical and that a directional asymmetry in vestibulo-ocular function or a head tilt does not necessarily correlate with a directional bias of subjective verticality.