Abstract
BackgroundTorso-based vibrotactile feedback may significantly reduce postural sway in balance-compromised adults during quiet standing or in response to perturbations. However, natural non-volitional postural responses to vibrotactile stimulation applied to the torso remain unknown.MethodsThe primary goal of this study was to determine, for two types of actuators (tactors) and in the absence of instruction, whether vibrotactile stimulation induces a directional postural shift as a function of stimulation location. Eleven healthy young adults (20 – 29 years old) were asked to maintain an upright erect posture with feet hip-width apart and eyes closed. Two types of tactors, Tactaid and C2, which differ in design and stimulation strength, were placed on the skin over the right and left external oblique, internal oblique, and erector spinae muscles in a horizontal plane corresponding approximately to the L4/L5 level. Each tactor of the same type was activated twice randomly for each individual location and twice simultaneously for all locations at a frequency of 250 Hz for a period of 5 s.ResultsVibration applied over the internal oblique and erector spinae muscle locations induced a postural shift in the direction of the stimulation regardless of the tactor type. For the aforementioned four locations, the root-mean-square (RMS) and power spectral density (PSD) of the body sway in both the A/P and M/L directions were also significantly greater during the vibration than before or after, and were greater for the C2 tactors than for the Tactaid tactors. However, simultaneous activation of all tactors or those over the external oblique muscle locations did not produce significant postural responses regardless of the tactor type.ConclusionThe results suggest that the use of a torso-based vibrotactile sensory augmentation display should carefully consider the tactor type as well as the instruction of corrective movements. Attractive instructional cues (“move in the direction of the vibration”) are compatible with the observed non-volitional response to stimulation and may facilitate postural adjustments during vibrotactile biofeedback balance applications.
Highlights
Torso-based vibrotactile feedback may significantly reduce postural sway in balance-compromised adults during quiet standing or in response to perturbations
Posture shifted in the direction of the vibrotactile stimulation during the per-vibration period
The average latency of vibration-induced postural shifts was 800 ms after the onset of vibration for both tactor types when vibration was applied over the left internal oblique location
Summary
Torso-based vibrotactile feedback may significantly reduce postural sway in balance-compromised adults during quiet standing or in response to perturbations. Since 2001, vibrotactile displays have been used in balance-related applications in which cutaneous stimulations provide information about body motion with respect to the gravito-inertial vector in order to inform corrective motor responses [11]. These volitional corrective responses have been associated with decreased postural sway in individuals with vestibular deficits [12,13,14,15,16,17], older adults [18], and healthy young adults [16,17,18,19] during quiet and perturbed stances. The most frequently used vibrotactile displays for balance-related applications have employed an array of either inertial or linear electromechanical actuators (tactors) placed along a belt worn horizontally around the torso [12,13,14,15,16,17,18,19]
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