中英雙語幼童語音處理中雙語轉移效應的神經機制

Abstract

雙語學習對孩童監控語言能力發展造成影響。在成人研究中，學習外語英文導致的轉移效應，使得中英文雙語者比起中文單語者，對於中文音韻知識有更高的覺察。然而，對於中英雙語幼童處理語音轉移效應，大腦運作的神經機制尚未有完整的理解。本研究對象為小學一年級孩童，包含29位中文單語孩童以及33位中英文雙語孩童。單語孩童進行中文聽覺語音判斷作業，雙語孩童分別進行中文與英文語音判斷作業，同時利用功能性近紅外光譜（fNIRS）量測其大腦皮質活動。在聽覺語音判斷作業中，孩童依序聆聽三個詞，並決定後兩詞中何者與首詞具有相同的韻首。作業依照詞首音素切割的難度，區分為困難及簡單兩個條件。在困難減去簡單條件的對比中，雙語孩童執行英文作業相較於中文作業，出現較強的左側角迴腦區活化，顯示英文語音處理需要較多不同詞彙表徵之間的轉換。此外，單語孩童相較於雙語孩童，在中文作業中出現較強的的左側中額下迴活化，推論單語孩童在中文語音處理中需要更多的選擇歷程。研究結果支持雙語轉移效應，推論雙語孩童的語音處理策略，包含字音至字形轉換歷程的涉入，而中文單語孩童則受到母語影響有較強的選擇歷程涉入。

Bilingualism is related to how children develop metalinguistic skills, being beneficial for learning languages mostly. For Chinese-English bilingual adults, compared to Chinese monolingual adults, learning an alphabetic language (e.g. English) allows them to become more aware of the phonological knowledge in Chinese. The neural substrates of phonological transfer, however, are still unknown in young Chinese children learning English. This study recruited 29 Chinese monolingual and 33 Chinese-English bilingual first graders. They performed an auditory phonological judgment task during fNIRS (functional Near Infrared Spectroscopy) neuroimaging. During the task, children heard three words in a sequential order and were instructed to choose the word that shared the same phonological onset with the first word. The difficulty of phonological segmentation had the hard and easy conditions. The bilingual children completed both Chinese and English tasks, whereas the monolinguals completed only the Chinese task. The contrast of the hard versus easy conditions was defined to reveal the hemodynamic activity in phonological processing. In the English task, bilingual children showed a trend of greater activation in the left angular gyrus relative to the Chinese task, demonstrating increased demands of mapping between phonological and orthographic representations of words. In the Chinese tasks, monolingual children showed greater activation in the mid-ventral region of left inferior frontal gyrus over bilingual children, suggesting more prominent selection process among multiple homophones in Chinese. The results of greater activation in the left angular gyrus support the idea of bilingual transfer effects, suggesting that bilingual children may involve the grapheme to phoneme conversion in phonological processing. Also, Chinese monolingual children may engage a brain area correlated with a selection process more in Chinese phonological processing.