Procedural and declarative memory in the acquisition of morphological knowledge: A model for second language acquisition in adults

Although there is a dominant notion that adults have a reduced and rather less effective language learning ability, there is ample evidence suggesting that the acquisition (learning) and retention (long-term memory) of procedural (skills) as well as declarative (facts, singular events) non-linguistic knowledge are robust in healthy adults. We investigated the effects of intensive, multi-session training on an artificial morphological rule (AMR) in adults, and tested whether key characteristics of non-linguistic skills are recognizable in linguistic rule learning. The AMR constituted phonological transformations of verbs expressing a semantic distinction, and was applied to repeated and new items. All participants learned to apply the AMR to repeated items, demonstrating key characteristics of procedural memory acquisition including group-average power-law like improvement in speed and accuracy, gains evolving both within-session and between-sessions (consolidation phase), and robust retention. The generalization to new items evolved separately for the phonological and semantic aspects of the AMR. Phonological aspects were rapidly generalized by all participants, independently of explicit (declarative) knowledge. However, the generalization of the semantic aspect required explicit discovery of its requisite role, and was not universally attained; when attained, additional training resulted in a further proceduralization phase. Our results show that adults are highly competent in acquiring and retaining linguistic knowledge, with both memory systems contributing differentially to the learning of distinct aspects of the morphological rule at different stages along the mastering of skilled linguistic performance. This is in line with a growing body of evidence suggesting that adults are as competent as, and often better than, children in acquiring and retaining non-linguistic skills.