语言转换的认知及其神经机制

The Cognitive and Neural Mechanism of Language Switch

语言转换是双语研究领域的焦点问题之一,抑制控制模型、语言特异性选择模型、任务设置惯性模型和序列难度效应模型从不同的角度解释了语言转换的认知机制。认知神经科学的一些研究发现,语言转换与任务转换具有类似的神经机制,说明语言转换代价与任务转换代价的本质可能是相同的。抑制控制和语言熟练程度如何影响语言的转换,语言转换代价与任务转换代价的本质是否相同,一般领域的抑制机制是否可以迁移到语言转换领域等问题是未来需要进一步研究的问题。

The asymmetry of language switch cost has been the focus in the field of language switch. Previous studies furred that the switching cost is symmetrical in proficient bilinguals, but asymmetrical in non-proficient bilinguals. Therefore, some researchers augured that language switch cost is affected by L2 proficiency. However, others proposed that inhibitory control is the real cause of the language switch cost. In short, many models have been proposed to explain this linguistic phenomenon from different perspectives. The inhibitory control model and the language-specific selection model are the two classical theories. The former holds that lexical selection in the two languages are realized through the practice of inhibition, the degree of inhibition leads to symmetrical or asymmetrical language switch cost. On the contrary, the latter insists that the language switch cost is modulated by L2 proficiency. In addition, other models attempt to explain the two classical theories from different angles. The task-set Inertia model is consistent with the inhibitory control model, both of which claim that inhibitory control plays a key role in language switch. Furthermore, the sequential difficulty effect model emphasizes language proficiency, which is in line with the language-specific selection model. Therefore, no agreement has been reached yet on the asymmetry of language switch cost. Cognitive neuroscience studies on inhibitory control and L2 proficiency have revealed the neural mechanisms of language switch. The fMRI studies on less proficient bilinguals have shown that language switch can activate the right prefrontal cortex （rPFC）, which reflects the role of inhibitory control, indicating that less proficient bilinguals need to rely on inhibitory mechanism to complete language switch successfully, and need to support the inhibitory control model. Nevertheless, some studies on proficient bilinguals found that rPFC was not activated. So they believed that language proficiency may modulate the symmetry of language switch cost, and that the language-specific selection model was correct. Moreover, cognitive neuroscience studies found that prefrontal cortex, anterior cingulate cortex （ACC） and left caudate nucleus were activated in language switch and task switch, indicating that the cost of language switch and task switch might be identical to some extent. Future research directions on language switch were pointed out in this paper. Specifically, （1） how do inhibition and language proficiency affect language switch？ If the language switch cost is symmetrical for high inhibitory control of less proficient bilinguals and proficient bilinguals, inhibitory control will be the real reason for language switch cost. If the language switch cost in proficient bilinguals is symmetrical, and asymmetrical for high inhibitory control of non-proficient bilinguals, L2 proficiency will be an important factor for language switch cost. （2） Are language switch cost and task switch cost of the same nature？ If the patterns of proficient and less proficient bilinguals in language switch cost and task switch cost are parallel, then the nature of the two tasks will be the same. If the language switch cost in proficient and less proficient bilinguals differs from the task switch cost, the language switch cost will at least be specific. （3） Can the inhibitory mechanism of domain-general task switch be generalized to language switch？ If language switch cost in non-proficient bilinguals is symmetrical after training, domain-general inhibitory training can be generalized to language switch. Otherwise, L2 proficiency will be the key factor in the language switch cost.