This thesis details the implementation and application of a robotic system for investigating the role of somatosensory feedback and the human vestibular apparatus in maintaining standing balance.

A 6 degree-of-freedom Stewart platform is employed to explore the human balance system in ways not possible during normal standing conditions. This robotic system, RISER (Robot for Interactive Sensory Engagement and Rehabilitation), uses a physics-based model to simulate of a variety of balance conditions for participants while they are secured to the system, making it possible to modify or isolate aspects of the balance control system for study.

The first study explores the role of somatosensory feedback using a robotic “ankle-tilt” platform, which was designed and implemented on the RISER system. The new platform enables independent manipulation of the ankles during balance simulations. Results demonstrate that providing accurate somatosensory feedback plays a significant role in improving balance control during standing simulations through reduction of sway amplitude and smoother motion during deliberate sway. The addition and validation of this platform opens new avenues for research involving incorrect, delayed, or partial somatosensory feedback, to study the effects of varying these parameters on balance performance.

In the second set of studies, a new technique is developed for investigating the gains and delays of the vestibular organs, employing the ankle-tilt platform. These studies utilized sinusoidal Galvanic Vestibular Stimulation (GVS) to generate an isolated vestibular error signal, producing sensations of motion. The RISER system is used to relate the response to GVS with the response to physical motions. The author investigates the perception and reflex responses to GVS using the RISER system, and demonstrates that sinusoidal GVS and rotation can be combined to produce superimposed perceptions or reflex responses. The author also compares the relationships frequency-dependant phase relationship between GVS and rotation, and finds that they do not conform to prior model expectations. Possible reasons for these discrepancies are examined, and repercussions on the existing understanding of the human balance model are considered.