Sway regularity reflects attentional involvement in postural control: effects of expertise, vision and cognition.

We examined the time varying (dynamic) characteristics of center-of-pressure (COP) fluctuations in a group of 14 preadolescent dancers and 16 age-matched non-dancers. The task involved maintaining balance for 20s with eyes open or eyes closed, and with or without performing an attention demanding cognitive task (word memorization). The main finding was that the time-dependent structure of the COP trajectories of dancers exhibited less regularity than that of non-dancers, as evidenced by a higher sample entropy (decreased statistical regularity). COP irregularity also increased during secondary task performance but decreased during standing with eyes closed. The combined findings indicate that the degree of attentional involvement in postural control - as reflected in the COP dynamics - varies along an automaticity continuum, and is affected by relatively stable subject characteristics (expertise) and more transient factors related to the attentional requirements of the task at hand.