Several definitions exist that offer to identify the boundaries between languages and dialects, yet these distinctions are inconsistent and are often as political as they are linguistic (Chambers & Trudgill, 1998). A different perspective is offered in this thesis, by investigating how closely related linguistic varieties are represented in the brain and whether they engender similar cognitive effects as is often reported for bilingual speakers of recognised independent languages, based on the principles of Green’s (1998) model of bilingual language control. Study 1 investigated whether bidialectal speakers exhibit similar benefits in non-linguistic inhibitory control as a result of the maintenance and use of two dialects, as has been proposed for bilinguals who regularly employ inhibitory control mechanisms, in order to suppress one language while speaking the other. The results revealed virtually identical performance across all monolingual, bidialectal and bilingual participant groups, thereby not just failing to find a cognitive control advantage in bidialectal speakers over monodialectals/monolinguals, but also in bilinguals; adding to a growing body of evidence which challenges this bilingual advantage in non-linguistic inhibitory control. Study 2 investigated the cognitive representation of dialects using an adaptation of a Language Switching Paradigm to determine if the effort required to switch between dialects is similar to the effort required to switch between languages. The results closely replicated what is typically shown for bilinguals: Bidialectal speakers exhibited a symmetrical switch cost like balanced bilinguals while monodialectal speakers, who were taught to use the dialect words before the experiment, showed the asymmetrical switch cost typically displayed by second language learners. These findings augment Green’s (1998) model by suggesting that words from different dialects are also tagged in the mental lexicon, just like words from different languages, and as a consequence, it takes cognitive effort to switch between these mental settings. Study 3 explored an additional explanation for language switching costs by investigating whether changes in articulatory settings when switching between different linguistic varieties could - at least in part – be responsible for these previously reported switching costs. Using a paradigm which required participants to switch between using different articulatory settings, e.g. glottal stops/aspirated /t/ and whispers/normal phonation, the results also demonstrated the presence of switch costs, suggesting that switching between linguistic varieties has a motor task-switching component which is independent of representations in the mental lexicon. Finally, Study 4 investigated how much exposure is needed to be able to distinguish between different varieties using two novel language categorisation tasks which compared German vs Russian cognates, and Standard Scottish English vs Dundonian Scots cognates. The results showed that even a small amount of exposure (i.e. a couple of days’ worth) is required to enable listeners to distinguish between different languages, dialects or accents based on general phonetic and phonological characteristics, suggesting that the general sound template of a language variety can be represented before exact lexical representations have been formed. Overall, these results show that bidialectal use of typologically closely related linguistic varieties employs similar cognitive mechanisms as bilingual language use. This thesis is the first to explore the cognitive representations and mechanisms that underpin the use of typologically closely related varieties. It offers a few novel insights and serves as the starting point for a research agenda that can yield a more fine-grained understanding of the cognitive mechanisms that may operate when speakers use closely related varieties. In doing so, it urges caution when making assumptions about differences in the mechanisms used by individuals commonly categorised as monolinguals, to avoid potentially confounding any comparisons made with bilinguals.

In the first decades of the 20th century, research on bilingualism was just beginning. The first studies on bilingual children proposed a substantial disadvantage with respect to intelligence and learning abilities. This first proposition was later discarded when Peal and Lambert (1962) suggested that, on the contrary, speaking two languages was providing children with significant advantages in their cognition. At the present time, it is assessed that, while knowing more than one language is not negative, the supposition that bilingualism might have positive effects on executive processing is subject to controversy. The Bilingual Executive Advantage (BEA) hypothesis has been tested many times and in several ways. Nevertheless, it appears more like an overstated theory rather than a real and proven fact. The purpose of this study is to contribute to this scholarly debate not only by conducting one more experiment but also by investigating a possible extension to the original hypothesis, more specifically, the possibility that additional languages might confer an even greater cognitive advantage than the one that has been claimed to exist for bilingual individuals. In the study, 23 young adults were tested on a version of the Attentional Network Task and a Colour-Shape switching task, both used in a previous study on professional interpreters (Babcock and Vallesi, 2017). The subjects were divided in two groups, bilinguals and multilinguals. The comparison of their performances in the two task revealed no significant difference in any of the examined measures.

Past research found performance differences between monolingual and bilingual children in the domain of executive functions (EF). Furthermore, recent studies have reported advantages in processing efficiency or mental effort in bilingual adults and children. These studies mostly focused on the investigation of “cold” EF tasks. Studies including measures of “hot” EF, i.e., tasks operating in an emotionally significant setting, are limited and hence results are inconclusive. In the present study, we extend previous research by investigating performance in a task of the “hot” EF domain by both behavioral data and mental effort via pupillary changes during task performance. Seventy-three monolingual and bilingual school children (mean age = 107.23 months, SD = 10.26) solved the Iowa Gambling Task in two different conditions. In the standard task, characterized by constant gains and occasional losses, children did not learn to improve their decision-making behavior. In a reversed task version, characterized by constant losses and occasional gains, both monolinguals and bilinguals learned to improve their decision-making behavior over the course of the task. In both versions of the task, children switched choices more often after losses than after gains. Bilinguals switched their choices less often than monolinguals in the reversed task, indicating a slightly more mature decision-making strategy. Mental effort did not differ between monolinguals and bilinguals. Conclusions of these findings for the bilingual advantage assumption will be discussed.