The goal of SARL is to design and assess technologies that strive to improve balance performance and quality of life in individuals with compromised balance function. Sensory substitution is a technique of augmenting or replacing compromised sensory information. In the context of balance impairments, a sensory substitution device gives corrective instructions to a user during balance-related exercises. We are currently studying the short- and long-term effects of training with vibrotactile biofeedback, the effects of vibrotactile cuing strategies on balance performance, and the effects of biofeedback during locomotor activities. Below are highlights from a few of our recently published research studies (see Publications page for links to the full research papers).
Cell phone-based balance trainer
Laboratory-based vibrotactile biofeedback systems are impractical for use in home rehabilitation balance training regimens due to their cost, size and complexity. We believe that wider, easier, and cheaper use of vibrotactile feedback devices can be achieved by exploiting the newest technologies, e.g. the increasingly powerful processors, considerable memory capacity, imbedded sensors (accelerometers), and high-resolution video in smartphones make these phones ideal candidates for easioy programmable, customizable feedback of body motion. This study designed, developed, and assessed a low-cost, small, lightweight, easy-to-use, cell phone-based balance trainer. This research is a major step towards developing a system that could eventually be used in the home to supplement balance rehabilitation exercises. A performance evaluation of the prototype cell phone-based balance trainer showed that it largely eliminated inherent sensor noise and provided a robust estimate for body tilt without significant time delay. When feedback was available, both healthy subjects and those with vestibular involvement significantly reduced their body sway. This study is the first to provide proof-of-concept for a portable balance rehabilitation system that has potential for broad accessibility.
This work was introduced in the iMedicalApps. Access the article here.
Real-time motion error detection and vibrotactile instructional cuing
The cost of physical therapy and the limited number of physical therapists can be prohibitive for some patients. In such situations, patients are commonly prescribed exercises to practice at home. However, compliance usually decreases over time due to the lack of feedback and instruction, and patients are often unable to precisely recall the proper procedures for the exercises. These challenges led to our motivation for developing a Mobile Instrument for Motion Instruction and Correction (MIMIC) system. The MIMIC system enables the physical therapist (expert) to map his/her movements to a patient (trainee) in a hands-free fashion. MIMIC comprises an expert module (EM) and a trainee modcule (TM). Both modules have six-degree-of-freedom inertial measurement units, microcontrollers, and batteries. The TM also has an array of actuators that give vibrotactile instructional cues to the patient. The therapist wears the EM, and an algorithm computes his/her relevant body position. The data captured is then transmitted wirelessly to the patient. Based on the computed differences between the motions of the therapist and the patient, directional instructions displayed via vibrotactile stimulation to the skin tell the patient to move in the direction of the vibration sensation until the vibration is eliminated. Based on the results of a proof-of-concept study conducted for healthy young adults, the subjects accurately reproduced the motion of bending at the waist using vibrotactile instructional cues.
Effects of biofeedback devices on postural stability in older adults
In laboratory settings, wearable biofeedback devices have been shown to improve balance in the elderly. However, their use requires the patient to interpret and respond to vibrations. Briefly the device works by monitoring trunk tilt. When the tilt becomes too great, the device delivers a vibration to the area of the trunk corresponding to the direction of lean, e.g. a vibration is applied to the left side when the wearer leans too far to the left.The theory of cognitive load states that people are limited in the amount of information they can process at any given time. Therefore we sought to characterize both postural and cognitive performance during a dual-task paradigm. Elderly subjects were asked to maintain an upright stance using the biofeedback device, and to respond as quickly as possible to a choice reaction time test. The most significant finding was that reaction times were greater when vibrations were delivered during the decision-making process of the choice reaction time test. These results indicate that while biofeedback instruction increases cognitive load, it is still very effective in improving balance metrics. We hope these results can inform the future development of balance prosthetics with the specific objective of decreasing cognitive load.
Natural tendency of posture in response to vibrotactile stimulation
This study aimed to determine whether vibrotactive stimulations applied to different locations on the torso induce directional postural responses and whether torso cutaneous information contributes to body representation. This is the first time we have been able to identify involuntary compensatory postural shifts in the direction of vibration when vibrotactile stimulation is applied over the internal oblique and erector spinae muscles. This study is the first step towards developing a portable motion instruction system incorporating the IMU and vibrotactile biofeedback that potentially can be used to instruct individuals as they perform common balance rehabilitation exercises.
Although the vibratory stimuli combination of two muscle groups results in the summation of postural responses, the effects of a combination of cutaneous stimuli applied to the torso remain unknown. Therefore, we also assessed whether co-vibrotactile stimulations (a vibration stimulus applied simultaneously over two skin areas) around the torsi has a summation effect on postural responses in the absence of instruction. The major finding is that co-vibration of homologous skin areas (symmetry relative to the mid-sagittal plan) over torso prime mover muscles induces significant postural shits. In addition, the direction of the shift corresponds to the vector summation of the directional shifts induced by vibrotactile stimulation applied individually to the respective skin areas of the test pairs found in a previous study.