Comparison of non-volitional postural responses induced by two types of torso based vibrotactile stimulations

The purpose of this study was to characterize the non-volitional postural responses to torso-based vibrotactile stimulation as a function of stimulation location for two types of vibrating actuators (tactors). Eleven young healthy adults were asked to maintain an upright erect posture with their eyes closed. Two types of tactors, Tactaid (electromagnetic inertial transducer) and C-2 (voice-coil-type linear transducer), were placed over the left and right external oblique, internal oblique, and erector spinae muscles in two different trial series. Regardless of the tactor type, vibration applied over the internal oblique and erector spinae muscles induced a postural shift in the direction of the stimulation. For these four locations, the root-mean-square (RMS) of the sway was significantly greater during vibration than immediately before or after stimulation. Vibration-induced postural shifts and increases in RMS sway were greater for the C-2 than Tactaid tactors. Simultaneous activation of all tactors or those over the external oblique muscles did not produce significant directional postural shifts or increases in sway, regardless of the tactor type. The directional shifts of posture suggest that these non-volitional responses should be considered to improve the use of torso-based vibrotactile sensory augmentation display designed for clinical balance applications.