Cognitive Brain Research Unit, Department of Psychology and Logopedics, Faculty of Medicine, University of Helsinki, Helsinki, Finland; Institute of Behavioural Sciences, University of Helsinki, Helsinki, Finland.
Division of Child Neurology, Helsinki University Central Hospital, Helsinki, Finland.
Neuropsychologia. 2017 Dec;107:108-120. doi: 10.1016/j.neuropsychologia.2017.11.016. Epub 2017 Nov 13.
How does the brain process and control languages that are learned at a different age, when proficiency in all these languages is high? Early acquired strong languages are likely to have higher baseline activation levels than later learned less-dominant languages. However, it is still largely unknown how the activation levels of these different languages are controlled, and how interference from an irrelevant language is prevented. In this magnetoencephalography (MEG) study on language switching during auditory perception, early Finnish-Swedish bilinguals (N = 18) who mastered English with high proficiency after childhood were presented with spoken words in each of the three languages, while performing a simple semantic categorisation task. Switches from the later learned English to either of the native languages resulted in increased neural activation in the superior temporal gyrus (STG) 400-600ms after word onset (N400m response), whereas such increase was not detected for switches from native languages to English or between the native languages. In an earlier time window of 350-450ms, English non-switch trials showed higher activation levels in the inferior frontal gyrus (IFG), pointing to ongoing inhibition of the native languages during the use of English. Taken together, these asymmetric switch costs suggest that native languages are suppressed during the use of a non-native language, despite the receptive nature of the language task. This effect seems to be driven mostly by age of acquisition or language exposure, rather than proficiency. Our results indicate that mechanisms of control between two native languages differ from those of a later learned language, as upbringing in an early bilingual environment has likely promoted automatiation of language control specifically for the native languages.
大脑如何处理和控制在不同年龄习得的语言，而这些语言的熟练程度都很高？早期习得的强势语言的基线激活水平可能高于后来习得的不占主导地位的语言。然而，人们仍然不清楚这些不同语言的激活水平是如何被控制的，以及如何防止无关语言的干扰。在这项关于听觉感知过程中语言转换的脑磁图（MEG）研究中，18 名早期习得芬兰语-瑞典语的双语者（均在童年后熟练掌握英语）在执行简单的语义分类任务时，会听到三种语言中的每一种语言的单词。从后来习得的英语转换到任何一种母语时，都会导致上颞回（STG）在单词出现后 400-600 毫秒（N400m 反应）时的神经激活增加，而母语到英语或母语之间的转换则没有检测到这种增加。在更早的 350-450ms 时间窗口中，英语非转换试验在额下回（IFG）中显示出更高的激活水平，这表明在使用英语时，母语被持续抑制。总的来说，这些不对称的转换成本表明，尽管语言任务是接受性的，但在使用非母语时，母语会受到抑制。这种影响似乎主要是由习得年龄或语言接触驱动的，而不是熟练度。我们的研究结果表明，两种母语之间的控制机制与后来习得的语言不同，因为在早期双语环境中成长可能促进了语言控制的自动化，特别是对母语而言。
