Bilingualism: Advantages and Disadvantages in Cognitive Processing, Language and Reading Comprehension

The overall aim of this study is, as suggested by Bialystok (2009), to investigate whether bilingual learners have an advantage in executive functions and a disadvantage in language compared to monolingual learners. In addition, the thesis examines whether the theory holds true for different groups of bilingual learners and different aspects of language and cognitive domains.

The study has a multi-method approach. It consists of a meta-analysis investigating the bilingual advantage theory in executive functions (EF) and two studies based on data from the longitudinal study The Stavanger Project—The Learning Child (The Stavanger Project). Study 2 uses data from the first wave of The Stavanger Project. The study investigates Norwegian language comprehension in a monolingual control group and three different groups of bilingual children at 2 years and 9 months. The three bilingual groups had different amounts of exposure to Norwegian. The third article is based on data from the fourth wave of The Stavanger Project and investigates different aspects of Norwegian language and reading skills across bilingual learners and a monolingual control group of 5^th graders. The sample in Study 3 is a subsample of the participants in Study 2; thus, the bilingual learners had been systematically exposed to Norwegian by early childhood education and care (ECEC) attendance and schools from at least the age of 2.

The thesis contributes three main findings. The first article provides little support for a bilingual advantage in overall EF. Moderator analysis targeting sample characteristics of bilingual subgroups that are theorized to have the largest bilingual advantage in EF shows no relation to the overall outcome of the analysis of differences in executive functions between bilingual and monolingual learners. Furthermore, there is limited evidence for a bilingual advantage in any EF domain. There is an advantage in switching, but not for all populations of bilingual learners.

The second article shows that bilingual toddlers have weaker second language comprehension skills than monolingual toddlers, but the differences in second language skills between different groups of bilingual learners are not fully explained by the time on task hypothesis. Bilingual children with mostly first language (L1) input at home had poorer Norwegian language comprehension than the two other bilingual groups. Bilingual toddlers with both first and second language input at home and bilingual toddlers with mostly second language input at home had equivalent second language skills. It therefore seems likely that a threshold value exists for the amount of second language input necessary to develop good second language skills rather than a direct relationship between the amount of input and language skills.

The third article shows that even after long and massive exposure to the second language, early bilingual 5^th graders have lower vocabulary depth, listening comprehension and reading comprehension in their second language than their monolingual peers. The difference cannot be explained by differences in socioeconomic status (SES). Their decoding and text cohesion vocabulary skills are equal to those of monolingual learners. In contrast to some other studies, the strength of the predictive path between different aspects of language skills and reading comprehension was found to be equal across language groups.

In total, these findings contribute to the knowledge base of what is typical development of language, reading skills and executive functions for different groups of bilingual learners. Without information of what is typical development for different bilingual groups, it is difficult to identify atypical development. Hence, the knowledge this thesis provides can support educators in identifying bilingual learners with learning disabilities earlier and with greater certainty, thereby reducing the risk of both over- and under-identifying bilingual learners in need of special needs education.