Balance Performance Measurment in a Phase Shifted Feedback Environment

Abstract

BALANCE PERFORMANCE MEASURMENT IN A PHASE SHIFTED FEEDBACK ENVIRONMENT By Craig Alan Hoovler, B.S. Applied Sciences, Concentration in Biomedical Engineering; B.A. Mathematics A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Biomedical Engineering at Virginia Commonwealth University. Virginia Commonwealth University, 2008 Director: Peter E. Pidcoe, P.T., D.P.T., Ph.D. Associate Professor, Department of Physical Therapy Commercial technologies for the objective assessment of balance exist in clinical settings. Training requires integration of sensory information to produce a coordinated motor response related to balance. These systems have had measurable phase delays of up to 250ms in the visual feedback provided to the patient. This provokes an unnatural response, requiring prediction from the subject. The proposed research investigates the impact of visual feedback phase delays on the performance of weight shift tracking tasks in a population of individuals with no known balance deficits. Visual feedback delays were investigated by simulating popular balance training software which utilizes force plates to measure center of pressure and display the results in a stimulus and response study. Ten healthy young-adult subjects with no known balance deficits were recruited to participate in this study. Subjects were asked to stand on a pair of force platforms that were linked to a computer. The system was designed to provide visual feedback corresponding to lateral weight shifts. A computer generated target provided a moving stimulus the subjects attempted to match. The stimulus files presented approximately 20 seconds of movement in a periodic (sinusoidal) or nonperiodic pattern. Stimulus frequencies ranged between 0.2 and 1.0 Hz with amplitude sufficient to require the subject to move safely within 50% of his/her base of support. Stimulus presentation was randomized and included both normal (control) and phase delayed (experimental) trials. Results of the experiment point to a noticeable improvement of performance with repeated trials. Regardless of introduced phase delays, study participants improved their performances as they were exposed to more trials, suggesting learning and predictive behavior. Random stimuli produced no noticeable improvements in performance across days of testing, as expected. Visual biofeedback systems may skew performance assessments of balance training because they contain periodic stimuli that are predictable.