Conscious awareness of motor fluidity improves performance and decreases cognitive effort in sequence learning

Motor skill learning is improved when participants are instructed to judge after each trial whether their performed movements have reached maximal fluidity. Consequently, the conscious awareness of this maximal fluidity can be classified as a genuine learning factor for motor sequences. However, it is unknown whether this effect of conscious awareness on motor learning could be mediated by the increased cognitive effort that may accompany such judgment making. The main aim of this study was to test this hypothesis in comparing two groups with, and without, the conscious awareness of the maximal fluidity. To assess the possible involvement of cognitive effort, we have recorded the pupillary dilation to the task, which is well-known to increase in proportion to cognitive effort. Results confirmed that conscious awareness indeed improved motor sequence learning of the trained sequence specifically. Pupil dilation was smaller during trained than during novel sequence performance, indicating that sequence learning decreased the cognitive cost of sequence execution. However, we found that in the group that had to judge on their maximal fluidity, pupil dilation during sequence production was smaller than in the control group, indicating that the motor improvement induced by the fluidity judgment does not involve additional cognitive effort. We discuss these results in the context of motor learning and cognitive effort theories.