A meta-analysis and meta-regression of serial reaction time task performance in Parkinson's disease

Objective: This article reports findings of a meta-analysis and meta-regression summarizing research on implicit sequence learning in individuals with Parkinson’s disease (PD), as measured by the Serial Reaction Time (SRT) task. Method: Following a systematic search of the literature, we analyzed a total of 27 studies, representing data from 505 participants with PD and 460 neurologically intact control participants. Results: Overall, the meta-analysis indicated significantly (p .001) worse sequence learning by the PD group than the control group. The average weighted effect size was found to be .531 (95% CI [.332, .470]), which is a medium effect size. However, moderate to high levels of heterogeneity (differences) were found between study effect sizes (I 2 58%). Meta-regression analysis suggested that presentation of the SRT task under dual task conditions coupled with PD severity or characteristics of the sequence might affect study effect sizes. Conclusions: The meta-analysis provides clear support that learning in procedural memory (procedural learning), which underlies implicit sequence learning in the SRT task, is impaired in PD.