Cognitive load suppresses explicit learning while sparing implicit learning in visuomotor adaptation

Limiting cognitive resources negatively impacts motor learning, but its cognitive mechanism is still unclear. Previous studies failed to differentiate its effect on explicit (or cognitive) and implicit (or procedural) aspects of motor learning. Here, we designed a dual-task paradigm requiring participants to simultaneously perform a visual working memory task and a visuomotor rotation adaptation task to investigate how cognitive load differentially impacted explicit and implicit motor learning. Over the three consecutive learning days, the control group without the dual task showed an increase in explicit learning and a decrease in implicit learning. In contrast, cognitive load, implemented by the dual task in the experimental group, selectively impaired explicit learning but spared implicit motor learning. Individual analysis uncovered a negative correlation between explicit learning and working memory performance, suggesting a trade-off between motor and cognitive tasks that compete for cognitive resources. Importantly, moderation analysis revealed that the relative increase in implicit learning was not directly influenced by cognitive load but rather indirectly by the changes in explicit learning. Specifically, individuals with more suppression in explicit learning from the dual task exhibited higher implicit learning. Our findings provide new insights into how cognitive load differentially affects explicit and implicit motor learning, as well as the interaction between explicit and implicit learning systems.<b>NEW & NOTEWORTHY</b> Motor skill acquisition is ubiquitously accompanied by cognitive load, yet its effects on motor learning remain understudied. Using a dual-task paradigm combining visual working memory and visuomotor adaptation, we found a striking dissociation: cognitive load suppresses explicit learning while paradoxically enhancing implicit learning. This enhancement can be explained by the compensatory relationship between explicit and implicit systems, rather than direct facilitation. Our findings revealed how the motor learning system adaptively reorganized under cognitive constraints.