Fig. 1

Illustration of the stimuli and task procedure for the handgrip–search dual task. Each trial began with the handgrip initiation to the required %MVC for 3 s with immediate visual feedback of exerted grip force shown on the screen. Participants were instructed to hold the grip force throughout the visual search task. For the visual search task, a search array appeared following a 1-s of center fixation and it stayed until the response (up to 3 s). The search array consisted of one target square and eight distractor circles evenly distributed on an imaginary circle. Each search item had a bar inside the outline shape. Participants were required to make a speeded response to report the orientation (vertical or horizontal) of the bar inside the target shape. On half of the trials, one of the circle distractors had a randomly chosen color background. This color singleton distractor often captures attention