The modern understanding of the term metacognition encompasses two levels of processing: a lower level awareness or knowledge of one’s own thoughts and a higher level regulation or control of our thinking. Metacognition, therefore, bears conceptual similarity with executive function: both are concerned with top-down monitoring and control of cognition in the service of ongoing goal-directed behaviour. Previous studies have shown a possible executive function advantage in multilingual speakers but also a possible disadvantage in metacognitive processing. To progress theory on metacognitive processing and the relationship with executive function and linguistic experience across the lifespan, we conducted a study testing 330 healthy individuals in four age groups from 7 to 80 years old. All participants performed a metacognition task and two measures of executive function, which included the Simon task and the Tower of London task. Half the participants were multilingual speakers since birth. We built developmental trajectories of metacognitive and executive function across the lifespan. The best metacognitive efficiency was observed in mid-adulthood, whereas the best executive function processing reached its peak in young adulthood. A steep cognitive decline was observed in older age, while metacognitive efficiency was preserved. Exploratory factor analysis indicated that metacognition and executive function are served by different factors across all ages. Contrary to previous findings in the bilingual literature, a multilinguistic experience conferred neither any significant advantage nor disadvantage in both executive function and metacognitive processing across the lifespan.

The development of verbal fluency is associated with the maturation of executive function skills, such as the ability to inhibit irrelevant information, shift between tasks and hold information in working memory. Some evidence suggests that multilinguistic upbringing may underpin disadvantages in verbal fluency and lexical retrieval, but can also afford executive function advantages beyond the language system including possible beneficial effects in older age. This study examined the relationship between verbal fluency and executive function in 324 individuals across the lifespan by assessing the developmental trajectories of English monolingual and multilingual children aged 7 to 15 years (N=154) and adults from 18 to 80 years old (N=170). The childhood data indicated patterns of improvement in verbal fluency and executive function skills as a function of age. Multilingual and monolingual children had comparable developmental trajectories in all linguistic and non-linguistic measures used in the study with the exception of planning, for which monolingual children showed a steeper improvement over the studied age range relative to multilingual children. For adults, monolinguals and multilingual participants had comparable performance on all measures with the exception of non-verbal inhibitory control and response times on the Tower of London task: monolinguals showed a steeper decline associated with age. Exploratory factor analysis indicated that verbal fluency was associated with working memory and fluid intelligence in monolingual participants but not in multilinguals. These findings raise the possibility that early acquisition of an additional language may impact on the development of the functional architecture serving high-level human cognition.

Research on speech comprehension in noise indicates that a multilinguistic experience may confer advantages in filtering out verbal interference, an effect observed both in children acquiring two or more languages since birth (Filippi, Morris, Richardson, et al., 2015) and in second language learner adults (Filippi, Leech, Thomas, et al., 2012). A possible interpretation for this advantage is that the multilingual mind is "trained" to control interference from the language not in use. This constant effort may support optimization of cognitive resources that are necessary for successfully selecting, processing and interpreting complex linguistic information. The present study aimed to extend this line of research by including a non-verbal interference condition. 209 typically developing children (132 English monolinguals and 77 multilinguals from different linguistic backgrounds) carried out a sentence interpretation task in the presence of verbal and non-verbal interference. We found no evidence for a reliable group difference in our data. Instead, findings indicated that background cognitive ability and socioeconomic status were the best indicators of successful control of interference, irrespective of whether participants were bilingual or monolingual. These findings are discussed in the light of previous research and, more widely, on the account of the current debate on the bilingual advantage.

Previous research has shown that cognitive development is sensitive to socio-economic status (SES) and multilinguistic experiences. However, these effects are difficult to disentangle and SES may modulate the effects of multilingualism. The present study used data from a large cohort of pupils who took part in the Study of Cognition, Adolescents and Mobile Phones (SCAMP) at ages 11–12 (T1) and 13–15 years old (T2). Cognitive measures were derived from tasks of cognitive flexibility, verbal, spatial and visuo-spatial working memory, speech processing and non-verbal reasoning. Using SES information collected through questionnaires (school type, level of deprivation, parental education and occupation), the sample was clustered into high/medium/low SES groups. Comparisons focused on 517 monolingual and 329 multilingual pupils in the high/low SES groups. Having controlled for multiple comparisons, the results indicated a significant beneficial effect of bilingualism in measures of working memory, visuo-spatial processing and non-verbal reasoning. These effects were present in both high and low SES individuals and sustained at both times of development, with a particularly significant improvement of working memory abilities in low SES bilinguals at T2 as compared to monolingual peers. Theoretical and practical implications of these findings are considered and guidance for educators is discussed.