Attention and control of posture: the effects of light touch on the center-of-pressure time series regularity and simple reaction time task.

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The stabilizing influence of a light touch (LT) on a postural sway has been consistently shown in the literature, however there is still no consensus in what way attentional resources are used when adopting LT during standing. To better elucidate the underlying mechanisms we introduced additional feedback (LT), which seems to distracts from postural control, and verified it by center of pressure (COP) regularity level and simple reaction time task. 25 healthy students randomly performed eight postural tasks, four without (NoRT)/ four with simple reaction task (RT). COP displacements were measured on a force plate in two visual conditions: eyes open/closed and two sensory conditions: without (NoLT)/with light touch (LT). Participants were asked to consider the postural task as the primary task. Although simple reaction time did not differ between postural conditions (p > 0.05), LT decreased postural sway velocity in anteroposterior direction (p < 0.001, η2 = 0.86) and decreased standard deviation (p < 0.001, η2 = 0.91) in both, reaction and visual conditions. Interestingly, RT task modified subjects behavior in NoLT conditions and caused slower COP velocity (p < 0.001, η2 = 0.53) without changes in signal regularity. Results also showed a significant increase in irregularity during standing with LT (p < 0.001, η2 = 0.86) in both vision and reaction conditions, suggesting that the signal was more random. Current results suggests that providing LT enhance postural steadiness and also seem to redirect attention externally, as shown by increased signal irregularity. Hence, LT possibly reduce the attention invested in the postural task itself. A RT task can be not sensitive enough to detect such subtle changes.