Vocabulary Size and Accuracy of Monolingual and Bilingual Preschool Children

Large numbers of children in the world are acquiring one language as their native language and subsequently learning another. There are also many children who are acquiring two or more languages simultaneously in early childhood as part of the natural consequences of being a member of bilingual families and communities. Because bilingualism brings about advantages to children that have an effect on their future development, understanding differences between monolinguals and bilinguals becomes a question of interest. However, on tests of vocabulary bilinguals frequently seem to perform at lower levels than monolinguals (Ben Zeev, 1977b; Doyle, Champagne, & Segalowitz, 1978). The reason for this seems to be that bilingual children have to learn two different labels for everything, which reduces the frequency of a particular word in either language (Ben Zeev, 1977b). This makes the task of acquiring, sorting, and differentiating vocabulary and meaning in two languages much more difficult when compared to the monolingual child’s task in one language (Doyle et al., 1978). Many researchers (Genesee & Nicoladis, 1995; Patterson, 1998; Pearson, Fernandez, and Oller, 1993) have raised questions about the appropriateness of using monolingual vocabulary norms to evaluate bilinguals. In the past, when comparing monolingual and bilingual performance, researchers mainly considered only one language of the bilingual (Ben Zeev, 1977b; Bialystok, 1988; Doyle et al., 1978). However, there is considerable evidence of a vocabulary overlap in the lexicon of bilingual children’s two languages, differing from child to child (Umbel, Pearson, Fernandez, and Oller, 1992). This vocabulary overlap is attributed to the child acquiring each language in different contexts resulting in some areas of complementary knowledge across the two languages (Saunders, 1982). It is crucial to examine both languages of bilingual children and account for this overlap in order to assess the size of bilinguals’ vocabulary with validity. This has been very difficult to do, since there are a few standardized measures for vocabulary knowledge in two languages concurrently and no measure are normed for bilingual preschool age children. It has been suggested that when the vocabulary scores of tests in both languages of the bilingual child are combined, their vocabulary equals or exceeds that of monolingual children (Bialystok, 1988; Doyle et al., 1978; Genesee & Nicoladis, 1995). However, this measure of Total Vocabulary (total scores achieved in language A + language B) is not sufficient for the examination of differences in vocabulary size of bilinguals and monolinguals due to the vocabulary overlap. A measure of total unique words or Conceptual Vocabulary, which is a combination of vocabulary scores in both languages considering words describing the same concept as one word, provides additional information about bilinguals’ vocabulary size with regards to knowledge of concepts. Pearson et al. (1993) conducted the only study considering both Total Vocabulary (language A + language B) and Conceptual Vocabulary (language A U language B) for bilingual children in comparison to their monolingual peers. Based on a sample of 25 simultaneous English/Spanish bilinguals and 35 monolinguals it was suggested that there exists no basis for concluding that the bilingual children were slower to develop early vocabulary than were their monolingual peers. There is a possibility that quite the opposite is true with regards to vocabulary comprehension when both languages are involved. There is a need for further study evaluating vocabulary size of preschool bilinguals to verify patterns identified by Pearson et al. (1993).