論文

Background: Lateralised language processing is a well-established finding in monolinguals. In bilinguals, studies using fMRI have typically found substantial regional overlap between the two languages, though results may be influenced by factors such as proficiency, age of acquisition and exposure to the second language. Few studies have focused specifically on individual differences in brain lateralisation, and those that have suggested reduced lateralisation may characterise representation of the second language (L2) in some bilingual individuals. Methods: In Study 1, we used functional transcranial Doppler sonography (FTCD) to measure cerebral lateralisation in both languages in high proficiency bilinguals who varied in age of acquisition (AoA) of L2. They had German (N = 14) or French (N = 10) as their first language (L1) and English as their second language. FTCD was used to measure task-dependent blood flow velocity changes in the left and right middle cerebral arteries during phonological word generation cued by single letters. Language history measures and handedness were assessed through self-report. Study 2 followed a similar format with 25 Japanese (L1) /English (L2) bilinguals, with proficiency in their second language ranging from basic to advanced, using phonological and semantic word generation tasks with overt speech production. Results: In Study 1, participants were significantly left lateralised for both L1 and L2, with a high correlation (r = .70) in the size of laterality indices for L1 and L2. In Study 2, again there was good agreement between LIs for the two languages (r = .77 for both word generation tasks). There was no evidence in either study of an effect of age of acquisition, though the sample sizes were too small to detect any but large effects. Conclusion: In proficient bilinguals, there is strong concordance for cerebral lateralisation of first and second language as assessed by a verbal fluency task.

The picture-word task presents participants with a number of pictured objects together with a written distractor word superimposed upon each picture, and their task is to name the depicted object while ignoring the distractor word. Depending on the specific picture and word combination, various effects, including the identity facilitation effect (e.g., DOG + dog) and the semantic interference effect (e.g., GOAT + cow), are often observed. The response patterns of the picture-word task in terms of naming latencies reflect the mechanisms underlying lexical selection in speech production. Research using this method, however, has typically focused on alphabetic languages, or involved bilingual populations, making it difficult to specifically investigate orthographic effects in isolation. In this paper, we report five experiments investigating the role of orthography in the picture-word task by varying distractor script (using the multiscriptal language Japanese, and pseudohomophonic spellings in English) across three different populations (Japanese monolinguals, Japanese-English bilinguals, and English monolinguals), investigating both the identity facilitation effect and the semantic interference effect. The results generally show that the magnitude of facilitation is affected by orthography even within a single language. The findings and specific patterns of results are discussed in relation to current theories on speech production.