Vocabulary growth and composition in monolingual and bilingual Basque infants and toddlers

The question as to whether there is a threshold value for input below which bilinguals do not achieve a monolingual-like development often arises. Although input does not seem to be determining for learning syntax, according to Juan-Garau and PSrez-Vidal, the amount of vocabulary acquired is proportional to the time of exposure. This article contributes to the current discussion with data from very young children exposed either to monolingual input of Basque or to different degrees of bilingual input of Basque and Spanish/French. The corpus for the present investigation has been extracted from the adaptation to Basque of the MacArthur-Bates communicative development inventories 1 and 2 questionnaires based on parental reports. These questionnaires, adapted to more than 40 languages throughout the world (www.sci.sdsu.edu/cdi), involve monthly data collection from different children for each age interval between ages 8 and 30 months and have proved to be a powerful instrument to establish normal linguistic development and deviance at an early stage. This study finds that the development of productive vocabulary in the four input groups established follows the tendencies described by Bates et al. but at different paces corresponding to different vocabulary sizes. In other words, the 'nominal bias' lasts to a higher age in the lower input groups, and the lexical diversity appears earlier in the higher input groups. Furthermore, lexical verbs, not predicates, are analysed as a separate category based on the study by Barrena and Serrat, which showed a higher proportion of verbs appeared in Basque as compared to the surrounding Romance languages. This tendency towards the use of verbs is confirmed in the data collected from input groups with higher exposure to Basque.