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Abstract

Both physical body roll and illusory roll evoked by full-field visual motion induce changes in blood pressure (BP) (Aoki et al. 2000 Clin. Aut. Res. 10: 23). How do these BP responses combine when both vestibular and visual information concerning roll are present? Subjects sat in a padded chair inside a 9ft diameter sphere, the inside surface of which was covered in high-contrast random dots. The chair and sphere could be independently rotated about the subjects' roll axis. Subjects were physically rolled clockwise from upright to right-ear-down at 7.6°/s, which took 12s. The sphere was rotated either alone, or so as to enhance (counter clockwise), oppose (clockwise), or null (clockwise at 7.6°/s) simultaneous physical roll. BP was continuously monitored by a finger plethysmograph throughout the movement and for several seconds following. Verbal reports of perceived body orientation were noted. BP typically increased from baseline levels during physical roll in the dark and the increase was maintained while subjects remained right-ear-down. The BP response to visually evoked roll was a transient increase reaching a peak at ∼6s. The BP changes in response to combinations of physical and visual roll were well described by a weighted linear sum of the responses to physical and visual motion presented separately even when the sphere remained earth stationary (the natural cue combination). The magnitude of perceived roll reported was accurate during roll in the dark and was systematically modulated by visual motion. These BP changes suggest that the autonomic responses to combinations of visual and vestibular cues reflect integration of information from the two systems.