Marco Dozza - PhD in Bioengineering, 2003-2007

Biofeedback Systems for Postural Control

Abstract :

Reliable sensory information and correct integration of sensory information are necessary for the control of posture. When sensory information is inadequate, such as in vestibular loss subjects, balance and postural control are impaired. Further, gradual loss of sensory information is also a consequence of the natural process of aging and is one of the major causes leading to falls in the elderly population.

Sensory information can be augmented by using biofeedback (BF) devices. BF devices are artificial systems able to provide additional movement information to their users. Although BF devices for postural control have been experimented since the 70s, the extent to which BF devices can substitute for missing sensory information for the control of posture is still unknown. Further, although BF devices have been suggested to be helpful for rehabilitation, no study to date has provided conclusive evidence that practice with BF is better at improving retention of motor performance than practice without BF.

The purpose of this dissertation are 1) to design, set-up and validate new-generation, portable, low-cost BF devices, 2) to determine how the design features of such BF devices influence postural control during static and dynamic motor tasks in vestibular loss and healthy subjects, 3) to elucidate how movement information from BF devices is integrated with sensory information for the control of posture, and 4) to understand the relationship between the effect of BF and spontaneous motor learning on postural control.

We implemented several types of BF devices that coded postural sway from bi-axial accelerometers, a combination of accelerometers and gyros, and a force plate into a stereo sound, vibrotactile stimulation to the trunk and/or a visual representation using different coding algorithms. By comparing such devices, we demonstrated how crucial the design of a BF device is, since it influences both the motor performance and the postural strategy of its user. In addition, we showed how vestibular loss and healthy subjects can use our audio-BF device to reduce sway by augmenting postural control without increasing muscular stiffness. Further, we found that audio-BF increases closed-loop control of posture and does not influence the open loop control of posture.

By testing bilateral vestibular loss and healthy subjects in several conditions of limited or inadequate sensory information, we showed how audio-BF efficacy is related to the individual dependency of each subject on vestibular, somatosensory, and visual information. In addition, we showed that audio-BF improves posture also in dynamic tasks such as standing on a randomly rotating surface and that the extent of these postural improvements is proportional to the amount of movement information coded into the sound. Also, we showed that spontaneous motor learning and audio-BF affect different ranges of frequency of postural control during standing on a randomly rotating surface.

Furthermore, unilateral vestibular loss subjects were tested during tandem gait using a cross-over design to understand whether tactile-BF of trunk tilt could improve postural performances during a complex, dynamic motor task such as gait. Results from this experiment showed that tactile-BF of trunk tilt acts similarly to natural sensory feedback in immediately improving dynamic motor performance and not as a method to recalibrate motor performance to improve dynamic balance function after short-term use.

Our results have many implications for the design of BF devices, for the understanding of motor control and sensory integration, and for the design of the protocols to be used with BF devices. More specifically, our results suggest that BF 1) needs a customized design for each subject and each task to optimally improve postural motor performance without facilitating undesirable postural strategies, 2) improves motor control in static and dynamic tasks by augmenting motor information and substituting for missing sensory information, 3) must be equipped with training protocols able to favor motor learning in order to became a helpful tool for balance and motor rehabilitation and training.

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