Abstract
The present study examined the impacts of effortful physical action on ongoing mental processes, specifically the efficiency of inhibiting perceptually salient but task-irrelevant distractor. To this end, we conducted a dual-task experiment with concurrent visual search task and handgrip task. In the search task, a target shape (square) appeared among nine homogeneous distractor shapes (circles) on an imaginary circle. Participants reported whether the direction of an orientation bar inside the target shape was vertical or horizontal as quickly and accurately as possible using a right-hand button press. Critically, one of the homogeneous distractors was presented in a different and salient color that was irrelevant for the task (color singleton present) on half of the trials, but not the other half of trials (color singleton absent). In the concurrent handgrip task, the participants squeezed a hand dynamometer, using left hand, to 5% or 40% of their individual maximum voluntary force (MVC) measured at the beginning of the study. The handgrip condition (5% versus 40%) and the color singleton condition (present versus absent) were randomly mixed across trials. Our results suggested that the singleton distractor effect, measured by the reaction time (RT) cost between the singleton present and absent conditions, increased from the low physical load to the high physical load condition. Furthermore, this detrimental effect of physical load significantly correlated with the extent of instability during force maintenance as well as the exerted force across the participants. Taken together, these results provide strong support that effortful physical action reduced inhibitory control of ongoing mental processes.