THE ROLE OF UTRICULAR STIMULATION IN DETERMINING PERCEIVED POSTURAL ROLL-TILT

We measured perceived postural orientation in roll in 5 subjects in tw o conditions which generate perception of bodily roll-tilt: firstly du ring roll-tilt on a tilt-chair in a l-g environment, and secondly duri ng constant velocity rotation 1 metre from the axis of rotation on a f ixed-chair human centrifuge. Perceived postural orientation was measur ed by the subjects' setting of a small motor-driven bar of light-emitt ing diodes, rotatable in the frontal plane, to the perceived gravitati onal vertical. The stimulus values on the tilt-chair and centrifuge we re selected so that they generated the same interaural utricular shear to the otolithic receptors in the inner ear. For such matched utricul ar shear stimuli, the subjects showed significantly smaller roll-tilt perception on the centrifuge than on the tilt-chair. This result shows that it is not utricular shear alone which is important for roll-tilt perception. Instead, at the stimulus values used here, perception cor responds to the angle of the resultant force, which is not given by ut ricular shear alone but from the ratio of utricular to saccular input Somatosensory input may complement this calculation.