The impact of bilingualism on executive functions in healthy adults

Approximately half of the world’s population is bilingual or multilingual. The bilingual advantage theory claims that the constant need to control known languages that are always active in the brain to use the one suitable for each specific context improves cognitive functions, specifically executive functions. However, some authors do not agree on the bilingual effect, given the controversial results of studies on this topic. This doctoral thesis aims to analyze the impact of bilingualism on executive functions. Two systematic reviews are presented in Chapters 1 and 3. The first is focused on investigating the effect of bilingualism on cognitive and motor inhibition; the second summarizes the results of studies that assessed language ability and executive functions using verbal fluency tasks. Subsequently, three experimental chapters are presented. The first study investigated cognitive and motor inhibition in the bilingual population and the effect of the task on performance. The second study analyzed verbal fluency performance using various variables such as qualitative, quantitative, and time-course indices. The last study explored the impact of the language used to perform the verbal fluency task by comparing the performance of a bilingual group who completed the test using both the dominant language and the L2. All chapters of the thesis are designed to investigate the effects that contribute to a bilingual advantage in executive functions. In general, the results of the two systematic reviews and the experimental data presented in this dissertation did not sustain the bilingual effect on the executive functions. The systematic review evidenced that the differences between language groups rarely emerge. The experimental studies failed to show differences in cognitive and motor inhibition ability, and no advantages in executive functioning emerge when considering the performance on the verbal fluency task. Moreover, bilinguals performed better when they completed the task in their dominant language.