Liquan Liu The Effects of Bilingualism on Infant Language Development : The Acquisition of Sounds and Words This dissertation discusses the influence of bilingualism on infant sound and word acquisition in the first two years of life . It studies whether monolingual and bilingual infants follow the same language developmental trajectory , and displays similarities and differences between monolingual and bilingual infants . Monolingual and bilingual infants from 5 to 18 months were tested on their perception of consonant , vowel , tone contrasts , and their associative word learning ability . Parents filled in a Communicative Development Inventory questionnaire , and a multilingual infant questionnaire designed by the author . In the sound perception experiments , no evident / clear delay was observed between monolingual and bilingual infants . For consonants , an early unstable perception pattern was observed in bilingual infants in the first year of life , leaving space for future research . Bilingual infants displayed more sensitivity than monolinguals in their perception of native vowels and non - native tones . In word acquisition , bilingual infants kept the same pace as monolinguals in their associative word learning performance , as well as receptive and expressive vocabulary size . In the questionnaire study , parents â intuition of their bilingual infants â degree of exposure to each language covered not only the languages directly spoken to their infants , but also the indirect linguistic input from the ambient environment . To integrate various findings , two hypotheses , the heightened acoustic sensitivity hypothesis and the minimum threshold hypothesis , were formed . This dissertation is of interest to psycholinguists , phonologists , and researchers on bilingualism and infant studies . The multilingual infant questionnaire is recommended as a tool of degree of exposure estimation for bilingual infants . ISBN : 978 - 94 - 6093 - 129 - 1
