Inclusion Criteria:  scheduled for cochlear implant CI surgery because of deafness minimum of five year history of documented absence of auditory & vestibular function, based on review of their audiograms & vestibular tests Specific vestibular criteria are: peak ice water caloric response of less than 3 deg/s for each ear; yaw VOR time constant < 3.0 sec and gain < 0.25; and reduced head impulse gain (<0.25) for all canal planes. Specific audiographic criteria: 80dB or greater sensorineural hearing loss in both ears  Exclusion Criteria:  pregnant not scheduled for cochlear implant/vestibular implant surgery unable to walk 50m other neurological disorder (other than migraine), otologic disease (other than presbycusis)