Online interference of declarative memory on fast and slow adaptive processes in force field motor learning

Error-based motor adaptation is currently understood as a dual-rate process involving a fast adaptive process that learns quickly but also decays rapidly and a slow process that learns slowly but has good retention. Although the fast process is typically categorized as procedural learning, recent evidence suggests that it relies on the declarative memory system. To test this hypothesis, we investigated in what manner a declarative memory task interferes with two processes that supposedly underlie force field adaptation in reaching. This declarative memory task, which involved learning a list of words, was assessed through either recognition or recall and was compared with a nondeclarative, vowel-counting task, using a within-subject design (n = 32). We used a Bayesian hierarchical dual-rate process model to capture the observed force compensation across trials, expecting that the parameters of the fast process would be affected by the declarative memory task. We examined the 95% highest density interval of the posterior distribution of the difference between the experimental and control conditions for each parameter. Although most parameters remained unaffected by the declarative memory task, the retention rate of the fast process showed a hint of reduction, suggesting a complex interplay between declarative memory and ongoing motor adaptation processes.NEW & NOTEWORTHY Motor adaptation involves fast and slow adaptive processes. Recent research suggests declarative memory interacts with the fast process. We studied how a declarative task affects trial-to-trial force field adaptation in reaching. Results showed no significant impact on the learning and retention of the slow process or on the learning of the fast process, but hint at a subtle role of declarative processes on the retention of the fast process.