The investigators will carry out a thorough investigation of the effects of electrical stimulation on vestibular and auditory function in a group of patients implanted with a modified cochlear implant providing extracochlear electrodes implanted in the vicinity of the of the ampullary nerve branches. These results will be compared to similar measurements carried out in a group of age and sex-matched healthy controls, in a group of patients with bilateral and unilateral vestibulopathy, and also in a group of patients implanted with a cochlear implant and normal vestibular function. The protocol comprises the following specific measurements:~Clinical evaluation of auditory function: pure-tone and speech audiometry.~Clinical evaluation of vestibular function: clinical evaluation of the vestibulo-ocular reflex (e.g., video-nystagmography, video-head impulse tests), and of the otolithic function (vestibular evoked myogenic potentials).~Dynamic visual acuity: loss of visual acuity while walking in a treadmill at controlled speed, compared to the static (standing in place) of the subject.~Auditory and vestibular brainstem evoked potentials.~Electroencephalography.~Temporal Binding Window: maximal time interval separating two different types of sensory stimuli (visual, auditory and vestibular) within which the subject still perceives them as simultaneous.~Psychophysical motion detection tests: motion perception thresholds measured in a platform allowing specific and smooth motion profiles in 3 linear and 3 angular dimensions.~Gait and posture: functional gait assessment, postural sway in conditions providing accurate or conflicting sensory (e.g., vestibular, visual, proprioceptive) information.~Spatial navigation in real and virtual reality environments (e.g. Morris water maze, standardized clinical environment).~Monitoring of the autonomous nervous system: standard, non-invasive clinical investigations of cardiovascular, ophthalmic, secretory, or metabolic functions (e.g., blood pressure, heart rate, pupillary reflex).
This study has three main goals (1) to explore the effects of electrical stimulations of the peripheral vestibular system(2) to assess the potential of this technique to rehabilitate basic vestibular functions in patients with severe bilateral vestibulopathy, and (3) to take advantage of the unprecedented experimental paradigm provided by the vestibular implant to increase our fundamental knowledge on the contribution of peripheral vestibular function to posture, gait and higher order sensory functions, mechanisms that remain poorly understood.