Measuring unilateral otolith function via the otolith-ocular response and the subjective visual vertical

In the present study, attention is directed to the unilateral response of t he otolith system to static and dynamic tilt, as reflected by subjective es timation of the visual vertical (oculogravic perception). Measurements were performed with a variable radius rotary chair, which permits controlled mo dulation of the centripetal, or radial, acceleration. By limiting the radiu s, i.e. eccentric displacement of the head by 3.5 cm during constant-veloci ty rotation about the earth-vertical axis, adequate unilateral stimulation of the otolith organ-predominantly the utricle-is generated, without involv ing the semicircular canals. This paradigm has been employed to measure the unilateral utriculo-ocular response, In contrast to the otolith-ocular res ponse (OOR), the subjective visual vertical (SVV) reflects the processing o f otolithic information in the higher brain centres (thalamus, vestibular c ortex). Exploitation of these two complementary approaches provides useful information for both experimental and clinical scientists. The findings als o reveal that centripetal acceleratory stimulation during constant angular velocity with the subject centred on axis is sufficient to localize periphe ral otolith dysfunction by means of SVV estimation. This represents a novel test of otolith function that can be easily integrated into routine clinic al testing.