Different mechanisms in learning different second languages: Evidence from English speakers learning Chinese and Spanish

Word reading has been found to be associated with different neural networks in different languages, with greater involvement of the lexical pathway for opaque languages and greater invovlement of the sub-lexical pathway for transparent langauges. However, we do not know whether this language divergence can be demonstrated in second langauge learners, how learner's metalinguistic ability would modulate the langauge divergence, or whether learning method would interact with the language divergence. In this study, we attempted to answer these questions by comparing brain activations of Chinese and Spanish word reading in native English-speaking adults who learned Chinese and Spanish over a 2 week period under three learning conditions: phonological, handwriting, and passive viewing. We found that mapping orthography to phonology in Chinese had greater activation in the left inferior frontal gyrus (IFG) and left inferior temporal gyrus (ITG) than in Spanish, suggesting greater invovlement of the lexical pathway in opaque langauges. In contrast, Spanish words evoked greater activation in the left superior temporal gyros (STG) than English, suggesting greater invovlement of the sublexical pathway for transparant languages. Furthermore, brain-behavior correlation analyses found that higher phonological awareness and rapid naming were associated with greater activation in the bilateral IFG for Chinese and in the bilateral STG for Spanish, suggesting greater language divergence in participants with higher meta-linguistic awareness. Finally, a significant interaction between the language and learning condition was found in the left STG and middle frontal gyrus (MFG), with greater activation in handwriting learning than viewing learning in the left STG only for Spanish, and greater activation in handwriting learning than phonological learning in the left MFG only for Chinese. These findings suggest that handwriting facilitates assembled phonology in Spanish and addressed phonology in Chinese. In summary, our study suggests different mechanisms in learning different L2s, providing important insights into neural plasticity and important implications in second language education.