The Joint Modulation of Language Distance and Task Demands on the Neural Mechanisms Underlying Bilingual Lexical Processing

Abstract: Whether bilinguals share the same neural mechanisms for processing their native language (L1) and second language (L2) is a long-standing question of debate. Extensive neuroimaging evidence has accumulated, yet substantial inconsistencies remain. These largely stem from linguistic distance between bilinguals’ L1 and L2, as well as differences in experimental task demands.
The present study used an activation likelihood estimation (ALE) meta-analysis to examine how linguistic distance and task demands affect brain activation during bilingual lexical processing. Seventy-four studies met the inclusion criteria and were classified into six groups according to task type (phonological, semantic, language switching) and language distance (Chinese–English bilinguals vs. alphabetic bilinguals): 18 on phonological processing in Chinese–English bilinguals, 12 on phonological processing in alphabetic bilinguals, 12 on semantic processing in Chinese–English bilinguals, 13 on semantic processing in alphabetic bilinguals, 9 on language switching in Chinese–English bilinguals, and 14 on language switching in alphabetic bilinguals. We carried out ALE meta-analyses using GingerALE 3.0.2. All coordinates were converted to Talairach space. To visualize the activation patterns, we projected the coordinates onto a standard brain template using BrainNet Viewer and xjview.
Results showed that during phonological tasks, Chinese–English bilinguals with a large language distance recruited greater L2-related activation in the left inferior parietal lobule, extending into the supramarginal gyrus, which is responsible for grapho-phonological conversion; whereas bilinguals of alphabetic languages with a small language distance shared the same neural mechanisms for their L1 and L2. During semantic tasks, Chinese–English bilinguals showed greater activation in the left middle frontal gyrus and left precuneus for L1 processing to support grapho-to-meaning conversion; whereas alphabetic bilinguals recruited the middle part of the left superior temporal gyrus more for their L1 to achieve phonology-to-meaning conversion, and for their L2 they activated language control brain regions including the left middle frontal gyrus/inferior frontal gyrus, insula, and inferior parietal lobule. Further comparison of brain activation between the two types of bilinguals during language switching tasks also revealed that alphabetic bilinguals with a small language distance required greater involvement of executive control brain regions, including the left inferior frontal gyrus, middle frontal gyrus, and inferior parietal lobule.
In sum, the current meta-analysis demonstrated that differences in brain activation between bilinguals' L1 and L2 processing reflect underlying cognitive processes jointly driven by linguistic distance and task demands. These findings not only support the specific computational demands hypothesis but also provide bilingual perspectives for understanding the universality and specificity of language processing.