Effect of Light Touch and Visual Tracking on Non-Linear Features of Postural Control System

Both the light touch (LT) of the fingertip on a surface and the visual tracking (VT) implementation can affect postural sway. In this study, we examined the individual effects of LT and VT performance on dynamic features of the postural control system and if LT plus VT provides an additional benefit for stance stability.
   In this repeated measures design, ten young, healthy individuals (29.80 ± 3.35 years) were instructed to maintain quiet standing in 4 test conditions: No Visual Tracking No Light Touch (N), Visual Tracking only (VT), Light Touch only (LT), Visual Tacking + Light Touch (VTLT).  The Repeated Measure ANOVA (2*2), the Wilcoxon test, and the Paired Student’s t-test were used. The significance level was set at P ˂ 0.05.
   The center of pressure (COP) sway decreased, and the COP Approximate Entropy (ApEn), Sample Entropy (SampEn), and Correlation Dimension increased with LT (P≤0.010). VT led to a significant decrease in COP sway (P=0.030) and a significant increase in COP anterior-posterior ApEn and SampEn (P<0.001). Compared to the N condition, changes of both linear and non-linear COP measures were greater in the VTLT condition than when LT or VT was performed individually.
   LT during quiet stance increased both the complexity and dimensionality of the postural control system in young healthy individuals which reflected the more automatic control of posture with LT. Besides, the performance of VT increased postural control complexity. Postural control is not only better adapted to perform individual LT and VT, but also there is a further adaptation of postural control to perform both LT and VT together. Adding VT to balance exercises using LT should be explored as an effective means to improve standing stability.