The effects of actuator selection on non-volitional postural responses to torso-based vibrotactile stimulation

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.

The Effect of Vibrotactile Cuing on Recovery Strategies From a Treadmill-Induced Trip

“…The moving contactor oscillates perpendicularly to the skin, and the surrounding skin area is shielded with a passive housing (3 cm in diameter). The tactor is driven by a 250 Hz sinusoidal signal generated by a customized control unit, and the peak-topeak displacement amplitude of the vibration is approximately 200 µm at the selected frequency [47].…”

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“…Since driving is a highly visual task, and the auditory channel is often occupied by radio, conversations, navigation system, external noises etc., it seems reasonable to distribute some information to the haptic channel. According to multiple resource theory [23], using the tactile channel might enlarge the total amount of information processed [22]. There are various motivating reasons for using tactile feedback in driving situations.…”

An Experimental Setup to Test Dual-Joystick Directional Responses to Vibrotactile Stimuli

“…• toward the stimulation [26] [27] [28]. Moreover, in [29], a preferred direction of intuitive response to vibrations on different body location has not been found.…”