Abstract: Normal postural control has traditionally been considered an automatic or reflex process using minimal attentional resources. Recent research has provided evidence against this assumption and shown that postural control could be influenced by posture-unrelated cognitive activity. However, it was not clear whether posture-cognition interferences were due to limited central information-processing capacity, or the U-shaped relationship between physiological arousal and postural control.
The purpose of the present study was to investigate the effect of concurrent cognitive activities on postural control with and without vision. To address this issue, a dual-task paradigm was used in the experiment. Eighteen young healthy adults aged from 21-35 years were asked to keep upright standing as still as possible for 60s (i.e. the primary task) in 2 (with/without cognitive task) × 2 (vision /no vision) test conditions. The order of the four test conditions were counter balanced across all subjects. Body sway was recorded from the top of head and evaluated by Root Mean Square (RMS), Mean Velocity (MV) and Romberg Quotient (RQ). A 2 × 2 ANOVA with repeated measures was performed on the data to examine the effects of cognitive task on postural control.
Results showed that the main effects of cognitive task and vision, the interaction of vision by cognitive task were significant on RMS and MV of body sway, as well as the RQ was decreased significantly when stance with cognitive task.
These findings suggested that concurrent cognitive activities hampered the visual control of standing posture. The posture-cognition interferences were due to the impeded of visual information processing. In addition, a strategy of freezing motor degrees of freedom (df-freezing strategy) would be adopted to decrease the body sway in higher cognitive-load conditions.

Key words: dual-task, postural control, attention, cognitive task, visual control