A longitudinal study of lexical development in very young French–English bilinguals is reported. The Computerized Comprehension Test (CCT) was used to directly assess receptive vocabulary and processing efficiency, and parental report (CDI) was used to measure expressive vocabulary in monolingual and bilingual infants at 16 months, and six months later, at 22 months. All infants increased their comprehension and production of words over the six-month period, and bilingual infants acquired approximately as many new words in each of their languages as the monolinguals did. Speed of online word processing was also equivalent in both groups at each wave of data collection, and increased significantly across waves. Importantly, significant relations emerged between language exposure, vocabulary size, and processing speed, with proportion of language exposure predicting vocabulary size at each time point. This study extends previous findings by utilizing a direct measure of receptive vocabulary development and online word processing.
