Age and amount of exposure to a foreign language during childhood: behavioral and ERP data on the semantic comprehension of spoken English by Japanese children.

Children's foreign-language (FL) learning is a matter of much social as well as scientific debate. Previous behavioral research indicates that starting language learning late in life can lead to problems in phonological processing. Inadequate phonological capacity may impede lexical learning and semantic processing (phonological bottleneck hypothesis). Using both behavioral and neuroimaging data, here we examine the effects of age of first exposure (AOFE) and total hours of exposure (HOE) to English, on 350 Japanese primary-school children's semantic processing of spoken English. Children's English proficiency scores and N400 event-related brain potentials (ERPs) were analyzed in multiple regression analyses. The results showed (1) that later, rather than earlier, AOFE led to higher English proficiency and larger N400 amplitudes, when HOE was controlled for; and (2) that longer HOE led to higher English proficiency and larger N400 amplitudes, whether AOFE was controlled for or not. These data highlight the important role of amount of exposure in FL learning, and cast doubt on the view that starting FL learning earlier always produces better results.