The emergence of action-effect-related motor adaptation amidst outcome unpredictability

Previous research indicates that quick, repetitive actions (pinches, taps, button presses) are executed with smaller force when followed by predictable and salient action effects (tones, light flashes). It has been suggested that successive actions become gradually softer until an optimum is reached, which presumably reflects a balance between the ability to maintain a high probability of action success, and the reduction of exerted force to conserve energy. In the present experiments, we investigated whether this action-effect-related motor adaptation appeared when the arrival of the action effect was unpredictable. Young adult participants produced evenly spaced pinches (Experiment 1) or taps (Experiment 2), which resulted in a tone in 50% of the trials. The presence of the tone effect varied randomly from trial to trial, leading to action sequences with various tone-elicitation patterns. We have found that pinches and taps preceded by sequences of tone-eliciting actions were softer than actions preceded by sequences of tone-absent trials. In the case of pinches, actions were also modulated on the fly, with the current action being softer and briefer when a tone was elicited. Our results demonstrate that action effects can modulate subsequent and ongoing actions even when the arrival of these effects is unpredictable. (PsycInfo Database Record (c) 2022 APA, all rights reserved).