Abstract
The incessant adaptation of posture to external visual cues is a complex task that requires the coordination of multiple degrees of freedom in order to maintain balance during performance of everyday actions. In the present study, we investigated the adaptation and learning of a rhythmical Weight Shifting (WS) task while providing either terminal or continuous visual cues during practice. Forty young healthy volunteers were randomly assigned in to one of four visual feedback groups (Continuous Target-Continuous Feedback, Continuous Target-Point Feedback, Point Target-Continuous Feedback, Point Target-Point Feedback). Participants were asked to perform periodic WS in the sagittal plane at a standard oscillation frequency (0.23 Hz) by matching the force exerted on a dual force platform to a target sine wave stimulus. Baseline, post-test, transfer (ankle tendon vibration at 80 Hz) and retention (24hs later) tests required performance of the same task guided by an auditory signal. Ground reaction forces were sampled through an A/D board (50 Hz) and analyzed using spectral and cross-correlation analysis. During practice, participants receiving terminal feedback, either as target or performance, had significantly lower aiming error and cycle variability compared to participants receiving continuous visual cues. On the other hand, the continuous feedback groups displayed significantly lower (closer to 1) performance-target power spectral signal ratios confirming higher accuracy throughout the course of WS. Learning was depicted in a reduction of cycle variability and a decrease of the median oscillation frequency towards the target frequency that was similar across all feedback groups. Nevertheless, participants practicing with terminal feedback showed better transfer of learning as this was confirmed by the reduced impact of the vibration stimulation on performance variables. It is suggested that terminal feedback reinforces the acquisition of a more flexible internal model of the perceptuo-motor transformation required for the performance of externally guided rhythmical whole-body movements.
The research leading to these results has received funding from the European Community's Seventh Framework Programme FP7/2007-2013 under grant agreement number 214728.