Differences in cognitive processing? The role of verbal processes and mental effort in bilingual and monolingual children's planning performance.

Past research documents a bilingual advantage in the domain of executive functions (EFs). However, controversial debates have questioned the robustness of those behavioral differences. The current study aimed to better understand the underlying cognitive prerequisites in bilingual students as compared with monolingual students and focused on two processes: the role of verbal processes, on the one hand, and mental effort during task execution, on the other. The use of self-regulatory speech has been found to be related to performance in tasks requiring EFs. For bilinguals who have grown up with two language systems from an early age, those relations are not fully understood. Furthermore, results from neuroimaging studies have shown that bilinguals might exhibit less mental effort in EF tasks. We investigated both processes in German-speaking monolingual elementary school students (n = 33; Mage  = 8.78 years) and German-Russian bilingual elementary school students (n = 34; Mage  = 8.88 years) solving a planning task. Results showed that monolinguals were impaired by a verbal secondary task in comparison with a motor control condition, whereas bilinguals performed in both tasks at an equal level, indicating a differential role of self-regulatory speech in both language groups. Analyses of changes in pupil diameter revealed less mental effort during task execution for bilingual children as compared with monolingual children. The current study adds to the existing literature by supplying further evidence for cognitive differences between monolingual and bilingual children.