Skill acquisition theorists conceptualize second language (L2) learning as the acquisition of a set of perceptual, cognitive, and motor skills. The dominant view in skill acquisition theory is to regard L2 skill acquisition as a three-stage process "from initial representation of knowledge through initial changes in behavior to eventual fluent, spontaneous, largely effortless, and highly skilled behavior" (DeKeyser, 2020, p. 83). While there is indirect evidence that indicates the existence of such developmental stages, the number and the nature of those stages are often assumed a priori, and whether or not these stages actually exist remains untested. My dissertation study was designed to test and validate the three-stage model of L2 skill acquisition derived from cognitive psychological research, namely, the cognitive, associative, and autonomous stage (Fitts & Posner, 1967), each of which draws on distinct cognitive processes for learning.Sixty-five adult learners deliberately learned and practiced a miniature language based on Japanese, called Mini-Nihongo, for a total of 1,056 practice trials. The participants also took a battery of tests on three dimensions of cognitive abilities that are known to be active at each stage of skill acquisition: declarative memory, procedural memory, and psychomotor ability (Ackerman, 1988, 1992; Anderson, 1982). Comprehension practice took place in the form of a sentence-picture matching task, and production practice was implemented in the form a productive maze task. Accuracy, reaction time (RT), and the coefficient of variability (CV) of RT were analyzed as the dependent variables. There were six tests of cognitive abilities: the Continuous Visual Memory Task and LLAMA-B for declarative memory ability, an alternating serial reaction time task and a statistical learning task for procedural memory ability, and the alternating serial reaction time task and a two-choice RT task for psychomotor ability.I analyzed the data from the language practice and the battery of cognitive tests in two steps. First, I fitted a series of hidden Markov models (HMMs) to the RT data that represented different hypotheses regarding the number of skill acquisition stages (i.e., one, two, or three stages). This first step of the analysis revealed that the acquisition of comprehension skills can be best conceptualized as a three-stage process, whereas the acquisition of production skills encompassed two stages.Based on the best-fitting HMMs and the corresponding number of learning stages, I then utilized a series of generalized linear mixed models to investigate the nature of the identified skill acquisition stages. Specifically, I examined whether the three dependent variables, accuracy, RT, and the CV, could be predicted by the three dimension of cognitive abilities at each stage of skill acquisition. The results showed that different cognitive abilities variably predicted learning at each stage, with the trends largely consistent with the general skill acquisition theory (DeKeyser, 2020; Lyster & Sato, 2013; Y. Suzuki, 2022).Overall, the findings of the study lend support to the three-stage model of L2 skill acquisition, but its proposed mechanisms may have to be revised to suit the specific cognitive processes involved in L2 learning. In addition, when applying the skill acquisition theory (or variants thereof) to L2 learning, one may have to analyze the theory not only at the level of learning mechanisms and processes (e.g., declarative learning, proceduralization, and production tuning) but also at the level of cognitive processing (e.g., lexical and grammatical de/encoding, syntactic parsing, and monitoring) that are specific to L2 learning.
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