Does articulation contribute to modifications of postural control during dual-task paradigms?

Many studies have been carried out to investigate the attentional resources required for postural control, using a 'dual-task' methodology in which performance on mental and postural control tasks is compared when these are carried out separately and concurrently. Most mental tasks used in these dual-task studies have employed verbal responses. However, changes in respiration during speech production are known to produce changes in postural control. Hence, the goal of this study was to determine whether articulation might contribute to the changes found in postural sway when a spoken mental task is being performed and to determine if the type of postural control measurement might also have an impact on the outcome of the study. Twenty young healthy participants were asked to stand on a force platform while executing secondary tasks that were performed silently or required a verbal response, and that required high or low levels of attention. Vision and postural task difficulty were manipulated. Performance of all tasks produced an increased sway frequency and decreased sway amplitude relative to the no task baseline. However, tasks that required articulation resulted in a more pronounced increase in postural sway frequency and sway path than did the tasks that did not require any articulation. These findings could imply that the addition of a secondary task results in increased stiffness, whereas articulation results in a further increased frequency of sway, which leads to an increase in sway path. We conclude that changes in the various parameters of sway that accompany performance of secondary tasks are complex, and are not always wholly attributable to attentional load, but may also be partly due to the motor requirements of the task, such as those involved in articulation.