Evaluation of anticipatory postural adjustment using the Simon task with cognitive load

Abstract

Many previous studies have been devoted to research intrinsic and extrinsic factors leading to falls. Recently, errors in the initial weight transfer of the postural responses prior to a step (anticipatory postural adjustment errors: APA errors), an indicative of motor program errors, and their possible relations to inhibitory control are reported. The purposes of the present study were to quantify the underlying mechanisms of APA errors and to investigate whether the APA error evaluation can potentially detect fall risks. 11 healthy young adults performed visually-cued step initiation tasks. We applied simple and choice reaction time tasks and the Simon task which consisted of congruent and incongruent conditions. Evidence of postural adjustment errors and stepping parameters were confi rmed with center of pressure obtained from a force plate. Results show that APA error rates were higher in the incongruent condition of the Simon task than the other tasks. The further analysis after dividing the trials according to whether APA error occurred revealed that the reaction time of APA error trials was shorter than non-APA error trials in both congruent and incongruent conditions. In addition, the foot-lift time of APA error trials was longer than non-APA errors trials. These results suggest that visual interference by the Simon task impaired judgment processes during stepping, leading to an increase in initial motor program errors, speeded reaction time and prolonged foot-lift time.