The development of audiovisual vowel processing in monolingual and bilingual infants: a cross-sectional and longitudinal study.
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The aim of the current dissertation is to investigate to what extent infants acquiring one language (monolinguals) and infants acquiring two languages (bilinguals) share their strategies during audiovisual speech processing. The dissertation focuses on typically developing Basque and Spanish monolingual and bilingual infants' processing of matching and mismatching audio-visual vowels at 4 and 8 months of age. Using an eye-tracker, the infants' attention to audiovisual match versus mismatch conditions and to the speakers' eyes versus mouth was measured in a cross-sectional and a longitudinal design. The cross-sectional data revealed that bilingual and monolingual infants exhibited similar audiovisual matching ability. Furthermore, they exhibited similar looking pattern: at 4 months of age, monolinguals and bilinguals attended more to the speakers' eyes, whereas at 8 months of age they attended equally to the eyes and to the mouth. Finally, the longitudinal data revealed that infants' attention to the eyes versus the mouth is correlated between 4 and 8 months of age, regardless of the linguistic group. Taken together, the current research demonstrated no clear difference in audiovisual vowel processing between monolingual and bilingual infants. Overall, the dissertation has made fundamental contributions to understanding underlying processes in language acquisition across linguistically diverse populations.