Extending the paradigm in L1 acquisition, scholars have begun to investigate whether participants’ domain-general ability to represent, encode, and integrate spectral and temporal dimensions of sounds (i.e., auditory processing) could be a potential determinant of the outcomes of post-pubertal L2 speech learning. The current study set out to test the hypothesis that auditory processing makes a unique contribution to L2 speech acquisition, for 70 Japanese classroom learners of English with different levels of L2 proficiency when biographical backgrounds (length of instruction and immersion) and memory abilities (working, declarative, and procedural memory) are controlled for. Auditory processing loaded onto modality-general capacities to represent and incorporate anchor stimuli (relative to target stimuli) into long-term memory in an implicit fashion, but dissociated from explicit abilities to remember, associate, and elaborate sensory information. Auditory processing explained a small-to-medium amount of variance in L2 speech learning, even after the other potentially confounding variables were statistically factored out.
In this study, neural representation of adult second language (L2) speakers’ implicit grammatical knowledge was investigated. Advanced L2 speakers of Japanese living in Japan, as well as L1 Japanese speakers, performed a word-monitoring task (proposed as an implicit knowledge test) in the MRI scanner. Behavioral measures were obtained from aptitude tests for explicit (language analytic ability) and implicit (statistical learning ability) learning. Findings indicate that, although both L1 and L2 speakers recruited neural circuits associated with procedural memory during the word-monitoring task, different brain regions were activated: premotor cortex (L1 speakers) and left caudate (L2 speakers). The premotor cortex activation was weaker in L2 than L1 speakers but was positively correlated with the left caudate activation, suggesting that their grammatical knowledge, while less automatized, was still developing. Behavioral sensitivity to errors was predicted only by explicit language aptitude, which may play a key role in the automatization of grammatical knowledge.
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