Brain plasticity and language learning

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A fundamental question in cognitive neuroscience is how the brain’s language-processing system develops and how it is affected by early language learning experiences. The work proposed takes advantage of natural linguistic situations to explore issues related to brain plasticity and language development, and combines high resolution structural and functional brain-imaging with behavioural testing. We propose four experiments in different language learners of Quebec that focus on persistence and attrition of language circuits related to early language-learning experience. Experiment 1 examines the neural basis of speech perception in simultaneous bilinguals (two languages from birth and highly proficient in both), sequential bilinguals (one language early and one language after age 5 years and highly proficient in both) and monolinguals (proficient in one language). Here we hypothesize that exposure to two languages from birth may allow a different structuring of perceptual space and, hence, a different neural organization from that observed in late L2 learners and, even more so, from that of monolingual speakers. Experiment 2 examines the nature of neural change related to intensive language training and how this impacts speech perception. Here we test the hypothesis that the perceptual window will be closed to learning new categories for late learners. Experiment 3 assesses whether training of these learner groups on a novel phonetic learning task (the Hindi dental-retroflex) will provide an advantage to those with earlier exposure to two language systems as compared to one, with the prediction that early perceptual structuring may generalize to new language-learning situations. We predict that early specialization with two sound-systems will permit generalization to novel patterns. Finally, in Experiment 4, we address the question as to whether, after abrupt loss of a language in infancy, the neural circuits still remain plastic, thus yielding an advantage to these speakers in the re-acquisition of this “first” language later in life, or whether these circuits are overwritten by another language experience, without providing any early advantage. Because it is thought that that the laying down of sound patterns is a process that potentially occurs during an optimal period early in development, the input received during this time may be crucial in understanding language abilities later in life. The program of research addresses the extent to which the human brain has the capacity to change as a result of language learning; that is, the extent to which neural patterns are fixed and the extent to which these patterns can be altered later in life. This work has strength in that we examine very specific changes in behavior, to make a link with how the brain changes through enhanced language learning, while concurrently examining the factors that contribute to more rapid or more successful learning in our individual participants. The results from these studies should confirm that neuroplasticity related to speech perceptual circuits can be observed even in adult brains and should shed light on how the brain changes in response to training. The proposed studies should help reveal the neural underpinnings of brain development in relation to age of language exposure and as such could lead to advances in language-education policies in Canada.