Abstract
Haptic cues are important for balance. Knowledge of the temporal features of their effect may be crucial for the design of neural prostheses. Touching a stable surface with a fingertip reduces body sway in standing subjects eyes closed (EC), and removal of haptic cue reinstates a large sway pattern. Changes in sway occur rapidly on changing haptic conditions. Here, we describe the effects and time-course of stabilization produced by a haptic cue derived from a walking cane. We intended to confirm that cane use reduces body sway, to evaluate the effect of vision on stabilization by a cane, and to estimate the delay of the changes in body sway after addition and withdrawal of haptic input. Seventeen healthy young subjects stood in tandem position on a force platform, with eyes closed or open (EO). They gently lowered the cane onto and lifted it from a second force platform. Sixty trials per direction of haptic shift (Touch → NoTouch, T-NT; NoTouch → Touch, NT-T) and visual condition (EC-EO) were acquired. Traces of Center of foot Pressure (CoP) and the force exerted by cane were filtered, rectified, and averaged. The position in space of a reflective marker positioned on the cane tip was also acquired by an optoelectronic device. Cross-correlation (CC) analysis was performed between traces of cane tip and CoP displacement. Latencies of changes in CoP oscillation in the frontal plane EC following the T-NT and NT-T haptic shift were statistically estimated. The CoP oscillations were larger in EC than EO under both T and NT (p < 0.001) and larger during NT than T conditions (p < 0.001). Haptic-induced effect under EC (Romberg quotient NT/T ~ 1.2) was less effective than that of vision under NT condition (EC/EO ~ 1.5) (p < 0.001). With EO cane had little effect. Cane displacement lagged CoP displacement under both EC and EO. Latencies to changes in CoP oscillations were longer after addition (NT-T, about 1.6 s) than withdrawal (T-NT, about 0.9 s) of haptic input (p < 0.001). These latencies were similar to those occurring on fingertip touch, as previously shown. Overall, data speak in favor of substantial equivalence of the haptic information derived from both “direct” fingertip contact and “indirect” contact with the floor mediated by the cane. Cane, finger and visual inputs would be similarly integrated in the same neural centers for balance control. Haptic input from a walking aid and its processing time should be considered when designing prostheses for locomotion.
Highlights
Powered exoskeletons enable persons with various walking problems to ambulate over the ground
When the cane was on the ground, the force recorded by the platform was
When the cane was lowered onto the ground (NT-T), the values of the M-L Center of foot Pressure (CoP) oscillations (Figure 1K) diminished in amplitude
Summary
Powered exoskeletons enable persons with various walking problems to ambulate over the ground. Several of these devices require the use of crutches to ambulate and maintain balance (Wang et al, 2015; see Asselin et al, 2016) Beyond their obvious mechanical effects (Bateni and Maki, 2005), crutches are a critical source of somatosensory inflow that provides information about body orientation with respect to the supporting surface through “extended physiological proprioception” (Simpson, 1974). In this exploratory study, we asked whether the stabilizing effect on static balance of haptic information from a cane can be likened to that of haptic input from a light fingertip touch or to that of vision. Addition of vision and haptic sense to the inherent proprioceptive inflow make the control of stance more effective (Jeka and Lackner, 1994, 1995; Sozzi et al, 2011, 2012; Honeine et al, 2015)
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