Brain plasticity and language learning

认知神经科学的一个基本问题是大脑的语言处理系统如何发展，以及它如何受到早期语言学习经验的影响。这项工作利用自然语言环境来探索与大脑可塑性和语言发展相关的问题，并将高分辨率结构和功能脑成像与行为测试相结合。我们提出了四个实验在不同的语言学习者的魁北克，专注于持久性和磨损的语言电路相关的早期语言学习经验。实验1探讨了同时双语者（两种语言从出生和高度熟练的两种），顺序双语者（一种语言早期和一种语言后，年龄5岁和高度熟练的两种）和单语者（精通一种语言）的言语知觉的神经基础。在这里，我们假设，从出生暴露于两种语言可能会允许不同的结构的感知空间，因此，不同的神经组织观察到在后期L2学习者，更是如此，从单语扬声器。实验2探讨了与强化语言训练相关的神经变化的性质以及这如何影响语音感知。在这里，我们测试的假设，感知窗口将关闭学习新的类别晚学习者。实验3评估是否培训这些学习者群体的一种新的语音学习任务（印地语的齿卷舌音）将提供一个优势，那些早期接触到两种语言系统相比，一个，预测早期的感知结构可能会推广到新的语言学习情况。我们预测，早期专业化与两个声音系统将允许推广到新的模式。最后，在实验4中，我们解决的问题，是否在婴儿期突然失去一种语言后，神经回路仍然保持可塑性，从而产生优势，这些扬声器在重新获得这种“第一”语言在以后的生活中，或者这些电路是否被另一种语言的经验，没有提供任何早期的优势。因为人们认为，声音模式的形成是一个可能发生在发展早期最佳时期的过程，在这段时间内接受的输入可能对以后的语言能力至关重要。该研究计划解决了人类大脑在多大程度上有能力改变语言学习的结果;也就是说，在多大程度上神经模式是固定的，以及这些模式在以后的生活中可以改变的程度。这项工作的优势在于，我们研究了非常具体的行为变化，通过增强语言学习与大脑如何变化联系起来，同时研究了有助于我们的个体参与者更快或更成功学习的因素。这些研究的结果应该证实，即使在成年人的大脑中也可以观察到与言语感知回路相关的神经可塑性，并且应该阐明大脑如何响应训练而发生变化。拟议中的研究应该有助于揭示大脑发育的神经基础与语言接触年龄的关系，因此可能会导致加拿大语言教育政策的进步。

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.