Assessment of Vibrotactile Feedback on Postural Stability During Pseudorandom Multidirectional Platform Motion

This study uses frequency-domain techniques and stabilogram diffusion analysis (SDA) to investigate the effect of vibrotactile feedback during continuous multidirectional perturbations of a support platform. Eight subjects with vestibular deficits were subjected to two-axis pseudorandom surface platform motion while donning a multiaxis vibrotactile feedback device that mapped body tilt estimates onto their torsos via a 3-row by 16-column array of tactile vibrators (tactors). Four tactor display configurations with spatial resolutions ranging between 22.5° and 90°, in addition to the tactors off configuration, were evaluated. Power spectral density functions of body sway in the anterior-posterior (A/P) and medial-lateral (M/L) directions, and transfer functions between platform motion and body sway, were computed at frequencies ranging from 0.0178 to 3.56 Hz. Cross-spectral analysis revealed that the A/P responses were not significantly driven by M/L inputs, and vice versa, thus supporting the notion of independent A/P and M/L postural control. Vibrotactile feedback significantly decreased A/P and M/L spectral power, decreased transfer function gains up to a frequency of 1.8 and 0.6 Hz in the A/P and M/L directions, respectively, and increased phase leads above 0.3 Hz. SDA showed significantly decreased transition time for both A/P and M/L tilts, and decreased transition displacement and short-term diffusion coefficients for A/P tilt. However, the spatial resolution of the tactor displays did not affect subjects' performance, thereby supporting the use of a lower spatial resolution display in future device designs.