Attention and control of posture: the effects of light touch on the center-of-pressure time series regularity and simple reaction time task
The stabilizing influence of a light touch 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 additional tactile information during controlling an upright posture. To better elucidate the underlying mechanisms we introduced conditions of both sensory deprivation (closing the eyes), additional feedback (light touch), which seems to distracts from postural control and verified it by introducing dual task paradigm (i.e. measuring simple reaction time to an unpredictable auditory stimulus). Twenty five healthy students randomly performed eight postural tasks, four with (RT) and four without simple reaction task (NoRT). Center of pressure displacements were measured on a force plate in two visual conditions: eyes open (EO), eyes closed (EC) and two sensory conditions: with light touch (LT), without light touch (NoLT). Before each measurement 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), additional tactile information in anteroposterior direction caused decreased postural sway velocity (p<0.001, {eta}2=0.86) and decreased standard deviation (p<0.001, {eta}2=0.91) in both, reaction and visual conditions relative to NoLT conditions. Interestingly, simple reaction task modified subjects behavior in NoLT conditions and caused slower COP velocity (p<0.001, {eta}2=0.53) without changes in signal regularity. Results also showed a significant increase in irregularity during standing with LT (p<0.001, {eta}2=0.86) in both vision and reaction conditions, suggesting that the signal was more random. Although there were no significant changes between length of the reaction time between postural conditions but there was strong effect of light touch on COP regularity, we can conclude that light touch is attention demanding but changes of flow of attention are very subtle in this simple postural tasks. Furthermore COP regularity analysis is sensitive to even such subtle changes.