The acquisition of a linguistic skill by adults: Procedural and declarative memory interact in the learning of an artificial morphological rule

How does practice make perfect in the acquisition of morphological skill in adults? Participants underwent intensive, multi-session training on an artificial morphological rule (AMR) requiring phonological transformations of verbs according to a semantic distinction. All participants learned to apply the AMR to repeated items, with a power law like improvement in speed and accuracy (group average), both within-sessions and between-sessions (consolidation phase) gains, and robust retention, as in non-linguistic skill learning. Generalization to new items evolved separately for different aspects of the AMR. Phonological aspects were generalized by all participants, independently of explicit (declarative) knowledge, and well fitted by a power function. However, the generalization of the semantic aspect required the explicit discovery of its requisite role, and was not universally attained; when attained, explicit knowledge of the semantic aspect of the AMR coincided with an abrupt increase in accuracy and initiated a phase of fluency gains (proceduralization). Our results suggest that both procedural and declarative memory contribute differentially to the learning of distinct aspects of a morphological rule, at different stages along the mastering of skilled linguistic performance.