Learning implicitly: Effects of task and severity after stroke

Background. Disparate results have been reported on the implicit learning ability of adults with stroke. Objective. This study aimed to elucidate the relationships between stroke severity and the task employed to test implicit motor learning. Methods. Twenty-eight patients with chronic stroke were divided according to stroke severity using the Orpington prognostic score into those with mild (n = 16, score < 3.2) or moderate stroke (n = 12, score 3.2-5.0). Seventeen healthy individuals served as matched controls (HQ. All participants practiced 2 implicit learning tasks, the Serial Reaction Time (SRT) and Serial Hand Movement (SHM). Results. A group-by-task-by-block interaction (P =.000) demonstrated differences across the experimental factors. Post hoc analyses revealed differences between groups and tasks. Greater change in the speed of responding was exhibited for the SHM than the SRT task by the HC and mild groups; however, the moderate group did not demonstrate a between-task difference. Conclusion. Both stroke severity and motor task influenced the magnitude of implicit learning across acquisition, which suggests for the first time that different tasks may yield disparate implicit learning outcomes in the same population. Additionally, the impact of stroke severity may be important when assessing residual implicit motor learning capability. The combination of these 2 factors helps explain previously reported contradictory findings and may inform future studies.