Exploring the cognitive effects of bilingualism: neuroimaging investigations of lexical processing, executive control, and the bilingual advantage

Bilingualism has been shown to influence a variety of cognitive functions, most notably lexical processing and cognitive control. These effects are both detrimental and advantageous. On the one hand, it has been proposed that bilinguals experience delayed lexical access compared to monolinguals, both in the less-proficient language and in the native language, due to the relatively reduced frequency of use. On the other hand, the constant need to juggle and control two languages enhances cognitive control abilities in bilinguals, such that they outperform monolinguals on tasks of executive processing and conflict resolution. This dissertation explores these cognitive changes associated with bilingualism, primarily through the use of a Stroop task. As it combines lexical processing with cognitive control, the Stroop task is a unique paradigm in which to investigate these abilities in bilinguals. Using behavioural measures, electroencephalography, and functional magnetic resonance imaging, the experiments presented here seek to deepen our understanding of lexical processing and cognitive control in bilingualism, in order to better understand how the now-common use of multiple languages affects the functional brain

Exploring the cognitive effects of bilingualism: neuroimaging investigations of lexical processing, executive control, and the bilingual advantage

Bilingualism has been shown to influence a variety of cognitive functions, most notably lexical processing and cognitive control. These effects are both detrimental and advantageous. On the one hand, it has been proposed that bilinguals experience delayed lexical access compared to monolinguals, both in the less-proficient language and in the native language, due to the relatively reduced frequency of use. On the other hand, the constant need to juggle and control two languages enhances cognitive control abilities in bilinguals, such that they outperform monolinguals on tasks of executive processing and conflict resolution. This dissertation explores these cognitive changes associated with bilingualism, primarily through the use of a Stroop task. As it combines lexical processing with cognitive control, the Stroop task is a unique paradigm in which to investigate these abilities in bilinguals. Using behavioural measures, electroencephalography, and functional magnetic resonance imaging, the experiments presented here seek to deepen our understanding of lexical processing and cognitive control in bilingualism, in order to better understand how the now-common use of multiple languages affects the functional brain

Electrophysiological explorations of the bilingual advantage: evidence from a stroop task

Bilinguals have been shown to exhibit a performance advantage on executive control tasks, outperforming their monolingual counterparts. Although a wealth of research has investigated this 'bilingual advantage' behaviourally, electrophysiological correlates are lacking. Using EEG with a Stroop task that manipulated the stimulus onset asynchrony (SOA) of word and colour presentation, the current study addressed two facets of the bilingual advantage. The possibility that bilinguals experience superior conflict processing relative to monolinguals (a 'conflict-specific advantage') was investigated by comparing behavioural interference effects as well as the amplitude of the Ninc, a conflict-related ERP component occurring from approximately 300-500 ms after the onset of conflict. In contrast, the hypothesis that bilinguals experience domain-general, conflict-independent enhancements in executive processing (a 'non-conflict-specific advantage') was evaluated by comparing the control condition (symbol strings) between groups. There was some significant, but inconsistent, evidence for a conflict-specific bilingual advantage. In contrast, strong evidence emerged for a non-conflict-specific advantage, with bilinguals demonstrating faster RTs and reduced ERP amplitudes on control trials compared to monolinguals. Importantly, when the control stimulus was presented before the colour, ERPs to control trials revealed group differences before the onset of conflict, suggesting differences in the ability to ignore or suppress distracting irrelevant information. This indicates that bilinguals experience superior executive processing even in the absence of conflict and semantic salience, and suggests that the advantage extends to more efficient proactive management of the environment

The Influence of Cross-Language Similarity on within- and between-Language Stroop Effects in Trilinguals

This study investigated effects of cross-language similarity on within- and between-language Stroop interference and facilitation in three groups of trilinguals. Trilinguals were either proficient in three languages that use the same-script (alphabetic in German–English–Dutch trilinguals), two similar scripts and one different script (Chinese and alphabetic scripts in Chinese–English–Malay trilinguals), or three completely different scripts (Arabic, Chinese, and alphabetic in Uyghur–Chinese–English trilinguals). The results revealed a similar magnitude of within-language Stroop interference for the three groups, whereas between-language interference was modulated by cross-language similarity. For the same-script trilinguals, the within- and between-language interference was similar, whereas the between-language Stroop interference was reduced for trilinguals with languages written in different scripts. The magnitude of within-language Stroop facilitation was similar across the three groups of trilinguals, but smaller than within-language Stroop interference. Between-language Stroop facilitation was also modulated by cross-language similarity such that these effects became negative for trilinguals with languages written in different scripts. The overall pattern of Stroop interference and facilitation effects can be explained in terms of diverging and converging color and word information across languages

Visual and linguistic narrative comprehension in autism spectrum disorders:Neural evidence for modality-independent impairments

Individuals with autism spectrum disorders (ASD) have notable language difficulties, including with understanding narratives. However, most narrative comprehension studies have used written or spoken narratives, making it unclear whether narrative difficulties stem from language impairments or more global impairments in the kinds of general cognitive processes (such as understanding meaning and structural sequencing) that are involved in narrative comprehension. Using event-related potentials (ERPs), we directly compared semantic comprehension of linguistic narratives (short sentences) and visual narratives (comic panels) in adults with ASD and typically-developing (TD) adults. Compared to the TD group, the ASD group showed reduced N400 effects for both linguistic and visual narratives, suggesting comprehension impairments for both types of narratives and thereby implicating a more domain-general impairment. Based on these results, we propose that individuals with ASD use a more bottom-up style of processing during narrative comprehension

The timing and magnitude of Stroop interference and facilitation in monolinguals and bilinguals

Executive control abilities and lexical access speed in Stroop performance were investigated in English monolinguals and two groups of bilinguals (English–Chinese and Chinese–English) in their first (L1) and second (L2) languages. Predictions were based on a bilingual cognitive advantage hypothesis, implicating cognitive control ability as the critical factor determining Stroop interference; and two bilingual lexical disadvantage hypotheses, focusing on lexical access speed. Importantly, each hypothesis predicts different response patterns in a Stroop task manipulating stimulus onset asynchrony (SOA). There was evidence for a bilingual cognitive advantage, although this effect was sensitive to a number of variables including proficiency, language immersion, and script. In lexical access speed, no differences occurred between monolinguals and bilinguals in their native languages, but there was evidence for a delay in L2 processing speed relative to the L1. Overall, the data highlight the multitude of factors affecting executive control and lexical access speed in bilinguals