The cognitive effects of bilingualism: does knowing two languages impact children’s ability to reason about mental states?

University of Minnesota Ph.D. dissertation. April 2010. Major: Child Psychology. Advisor: Dr. Maria D. Sera. 1 computer file (PDF); ix, 116 pages, appendices A-B.In a number of studies, bilingual children have been shown to outperform monolingual children in false belief tasks, thus providing evidence that bilingualism affects children's ability to reason about the mental states of others. However, there are two limitations to this past work. The first limitation is that false belief tasks only measure a limited aspect of children's mental state reasoning abilities. Thus, performance in false belief tasks cannot be assumed to reflect a general ability to reason about the mental states of others. Secondly, the language skills of the bilingual groups included in this past work were only reliably measured in one language. Thus, we do not have a good understanding of how language proficiency across both languages impacts mental state reasoning abilities. In order to address these limitations, 3- to 5-year-old Spanish-English bilingual children and English monolingual children were tested using Wellman and Liu's (2004) scale which assesses a variety of aspects of mental state reasoning. The scale includes the following tasks: a Diverse Desires task, a Diverse Beliefs task, a Knowledge Access task, a Contents False Belief task, an Explicit False Belief task, a Belief-Emotion task, and a Real-Apparent Emotion task. Additionally, the language proficiency of the bilingual group was measured in both English and Spanish using standardized measures of vocabulary comprehension (the PPVT and the TVIP). Results indicate that when English vocabulary level was controlled, the bilingual children outperformed the monolingual children in the Diverse Desires task. Furthermore, effect sizes suggest that the bilingual children also outperformed the monolingual children in the Knowledge Access, Belief-Emotion, and Real-Apparent Emotion tasks when English vocabulary level was controlled. Overall, these findings provide evidence that bilingualism contributes to a broader effect on mental state reasoning than has been previously found