Increasing the cognitive demand of upper-limb psychomotor tasks increases the perception of effort

The motivation intensity theory suggests that the perception of effort (PE) reflects the self-monitoring of resources and is used to self-regulate goal-directed actions. Resource monitoring and self-regulation are typically studied separately in the motor or cognitive domain. Here, we tested the effect of cognitive demand on PE in two psychomotor tasks (experiment 1), and we examined the effect of prescribing a target level of PE intensity on performance (experiment 2). In experiment 1 (n = 20, within-participants), we used fixed tempo during two upper-limb psychomotor tasks (Box and Block Test and pointing task) with PE as dependent variable. In experiment 2 (n = 20, within-participants), we used fixed PE during a self-paced pointing task with PE as independent variable. In both experiments, heart rate, respiratory rate, and biceps/triceps brachii electromyographic signal were monitored. Cognitive demand was manipulated (low, moderate, high) via a Stroop task, determining which block to move or target to reach. In experiment 1, PE increased with increased cognitive demand to maintain performance in both tasks. In experiment 2, higher cognitive demand during self-paced pointing at fixed PE led to decreased performance. Heart rate proved most sensitive to cognitive demand changes among physiological variables but failed to reflect the increase in cognitive demand from low to moderate in experiment 1. These results confirm the possibility of using the PE to prescribe and monitor the intensity of a psychomotor task. This study opens perspectives to investigate the neurophysiology of PE and the unicity or duality of effort (cognitive vs. motor).