Haptic Information Improvement on Postural Sway is Information-Dependent But Not Influenced by Cognitive Task.

Young adults reduce their sway in both light touch (LT) and anchor systems (AS), however, the cognitive involvement in these tasks is unknown. This study investigated postural control in young adults standing upright using either LT or AS, concomitantly with a cognitive task (counting). Nine adults (26 ± 7.4 years) stood in the upright tandem stance with eyes closed, with/without LT, AS (force <2 N), and a cognitive task. The mean sway amplitude of the trunk, right wrist, and shoulder ellipse area, as well as the mean force during LT and AS were obtained. The cognitive task did not influence the magnitude of trunk sway or the mean force in the LT and AS conditions. The trunk sway magnitude was reduced in the AS and even further in LT. Wrist and shoulder variability was larger in the AS than in the LT. Based on these results, we conclude that enhanced sensory cues provided by LT and AS reduce trunk sway with little or no attentional demands.

Trunk and head displacements stabilized to perform both horizontal and vertical saccadic eye movements.

Vision is crucial for humans to interact with their surrounding environment, and postural sway is reduced to allow short eye movements. However, the extent of subtle changes in postural control for horizontal and vertical eye movements remains unclear. The goal of this study was to investigate the effects of vertical and horizontal eye movements on head and trunk control in young adults. Fifteen healthy adults (23.4 ± 4.7 years) stood upright in three conditions for 60 s: fixation, horizontal, and vertical guided eye movements. In fixation, participants had to fixate on a stationary target. In both the horizontal and vertical eye movements, the target was presented with a frequency of 0.5 Hz and a visual angle of 11°. Eye displacement was monitored using a SMI eye tracker (ETG2.0) and trunk and head sway were monitored using infrared markers (Optotrak 3020, NDI). The mean sway amplitude was lower in both directions for eye movements and lowest in the vertical direction compared to the fixation condition. The sway area was also lower in vertical eye movement than in the fixation condition. We also found that the sway reduction was greater at head than at trunk level. The median frequency sway in the anterior-posterior direction was higher in both eye movements than in fixation. Based upon these results, we suggest that to perform short eye movements, postural sway is more strongly controlled at the head level than at the trunk and in vertical eye movements than in horizontal movements.