Effects of visual interference on initial motor program errors and execution times in the choice step reaction.

The purpose of this study was to examine whether visual interference has any effect on error in the initial direction of anticipatory postural adjustment (APA) prior to a step (indicating a motor program error) and response time during the choice step execution. Twenty healthy young participants were instructed to execute forward stepping as quickly and accurately as possible on the side indicated by a central arrow (←, left vs. →, right) of a visual cue in the neutral condition. In the flanker condition, they were additionally required to ignore the 2 flanking arrows on each side (→→→→→, congruent or →→←→→, incongruent). Errors in the direction of the initial weight transfer (APA errors) and the step execution times were measured from the vertical force data. In the incongruent condition, the percentage of APA errors and the step execution times were significantly greater than those in the neutral and congruent conditions. A linear mixed model revealed that the step execution time in trials with APA errors was longer than those in trials without APA errors. The visual interference effect of a flanker task may load selective attention and judgment processing during movement initiation, leading to increased initial motor program errors and prolonged step execution times even in healthy young adults.