Bilateral loss of vestibular function (inner ear balance sensation) is disabling, with affected individuals suffering chronic disequilibrium, increased risk of falls, and inability to maintain stable vision during head movements typical of daily life. Whil most individuals with partial loss compensate through rehabilitative strategies enlisting other senses, those with profound loss who fail to compensate have no good therapeutic options. Because the vestibular nerves are intact in many such cases, electrical stimuli encoding head rotation should be able to drive the nerve and restore sensation of head movement, much like a cochlear implant restores auditory function. The proposed research program represents the fourth step of a five-step plan to develop an effective treatment for individuals disabled by bilateral vestibular deficiency. Step 1 was to establish a neurophysiologic foundation for prosthetic restoration of the 3D VOR in rodents. Step 2 comprised development of the first multichannel, head-mounted vestibular prosthesis able to restore sensation of 3D head rotation. Step 3 optimized stimulus protocols and electrode designs in rodents and then transitioned experiments from acute to chronic and from rodents to nonhuman primates. Step 4 - the current proposal - will translate MVP technology from rhesus monkeys to humans via an early feasibility study of a modified cochlear implant adapted to serve as a vestibular prosthesis, setting the stage for final revisions to MVP designs and a subsequent, large-scale pivotal trial.