<p>Bilingualism and its effect on individuals have been studied within different disciplines. Although the first psychological study of bilingualism was couducted by Cattell as early as 1887, only a few studies have exclusively investigated the effect of bilingualism on memory systems’ functioning. In the field of cognitive psychology of bilingualism, there is some evidence for the positive influence of bilingualism on children’s cognitive ability across various domains but there is little knowledge about the relationship between bilingualism and memory in a lifespan perspective. This thesis’s main aim was to investigate memory systems’ functioning and development in bilingual individuals. To this end, two studies were performed: a cross-sectional study of bilingual children (Study I) and a longitudinal study of young and older adults (Study II). The purpose of Studies I and II was to determine whether there are differences between monolinguals and bilinguals regarding various memory systems’ functioning. Study I compared monolingual and bilingual children’s performance on episodic and semantic memory, and Study II investigated performance on episodic and semantic memory in bilingual younger and older adults. Specifically, these studies aimed to examine a) which memory systems will be affected more as a function of language, and b) to what extent the differences would manifest themselves during a subject’s lifespan. The purpose of Study III was to explain the relation among word representations, lexical access and lexical selection in a bilingual word production paradigm. In this study, a model of bilingual production was developed to explain the results and clarify the role of automatic and controlled processes in using two languages. The results of Studies I and II showed a superiority of bilinguals over monolinguals as well as a variation of association between memory performance and bilingualism across different periods of adulthood. It appears that the lifelong experience of managing two languages enhances control processes, which in turn play an important role in enhancing memory performance. Using a “dual mechanism model”, Study III explains the efficiency of inhibitory processing when having two languages activated.</p>

Bilingualism and its effect on individuals have been studied within different disciplines. Although the first psychological study of bilingualism was couducted by Cattell as early as 1887, only a few studies have exclusively investigated the effect of bilingualism on memory systems’ functioning. In the field of cognitive psychology of bilingualism, there is some evidence for the positive influence of bilingualism on children’s cognitive ability across various domains but there is little knowledge about the relationship between bilingualism and memory in a lifespan perspective. This thesis’s main aim was to investigate memory systems’ functioning and development in bilingual individuals. To this end, two studies were performed: a cross-sectional study of bilingual children (Study I) and a longitudinal study of young and older adults (Study II). The purpose of Studies I and II was to determine whether there are differences between monolinguals and bilinguals regarding various memory systems’ functioning. Study I compared monolingual and bilingual children’s performance on episodic and semantic memory, and Study II investigated performance on episodic and semantic memory in bilingual younger and older adults. Specifically, these studies aimed to examine a) which memory systems will be affected more as a function of language, and b) to what extent the differences would manifest themselves during a subject’s lifespan. The purpose of Study III was to explain the relation among word representations, lexical access and lexical selection in a bilingual word production paradigm. In this study, a model of bilingual production was developed to explain the results and clarify the role of automatic and controlled processes in using two languages. The results of Studies I and II showed a superiority of bilinguals over monolinguals as well as a variation of association between memory performance and bilingualism across different periods of adulthood. It appears that the lifelong experience of managing two languages enhances control processes, which in turn play an important role in enhancing memory performance. Using a “dual mechanism model”, Study III explains the efficiency of inhibitory processing when having two languages activated.