Human cortical responses to congruent and incongruent combinations of visual and vestibular stimuli
43.505, Monday, May 13, 8:30 am - 12:30 pm, Vista Ballroom
Jac Billington1, Andrew Smith2; 1Institute of Psychological Sciences, University of Leeds, Leeds, LS2 9JT, 2Dept of Psychology, Royal Holloway, University of London, Egham TW20 0EX
Processing of visual cues to egomotion has been associated with hMST, hPIVC and CSv. All three areas are also implicated in vestibular processing (Smith et al. Cerebral Cortex, 2012). We explored whether and how vestibular and visual signals are combined in these regions. Whilst some neurons in macaque MSTd show the same directional tuning in both modalities, some show incongruent tuning preferences, suggesting a role in cancelling the effect of rotational head movements on optic flow during self-motion. We measured the perceptual magnitude of roll induced by galvanic vestibular stimulation (GVS) and measured the vestibulo-ocular reflex (VOR). GVS was then combined with fMRI to assess responses to matched vestibular and visual stimuli in two combinations: (i) visual rotation induced by GVS, nulled by counter-rotation of the visual stimulus and (ii) visual stimulus rotation in the same direction and with the same retinal magnitude as that induced by GVS. Responses in hMST, hPIVC and CSv were similar in both conditions. This result suggests that these areas respond to the degree of retinal motion, as opposed to the degree of motion consciously perceived. Such patterns of response may reflect the presence of populations of visual-vestibular neurons which are involved both in representing head rotation for perception of self-motion and in cancelling the visual effect of head rotation when computing object motion within the visual scene.