The Neural Cost of the Auditory Perception of Language Switches: An Event-Related Functional Magnetic Resonance Imaging Study in Bilinguals

Abstract

One of the most remarkable abilities of bilinguals is to produce and/or to perceive a switch from one language to the other without any apparent difficulty. However, several psycholinguistic studies indicate that producing, recognizing, and integrating a linguistic code different from the one in current use may entail a processing cost for the speaker/listener. Up to now, the underlying neural substrates of perceiving language switches are unknown. In the present study, we investigated the neural mechanisms of language switching during auditory perception in bilinguals. Event-related functional magnetic resonance imaging was performed in 12 early, highly proficient Italian/French bilinguals, who were more exposed to their second language. Subjects had to listen to narratives containing "switched passages" that could either respect (i.e., regular switches) or violate (i.e., irregular switches) the constituents of sentence structure. The results indicate that switching engages an extensive neural network, including bilateral prefrontal and temporal associative regions. Moreover, a clear dissociation is observed for the types of switches. Regular switches entail a pattern of brain activity closely related to lexical processing, whereas irregular switches engage brain structures involved in syntactic and phonological aspects of language processing. Noteworthy, when switching into the less-exposed language, we observed the selective engagement of subcortical structures and of the anterior cingulate cortex, putatively involved in cognitive and executive control. This suggests that switching into a less-exposed language requires controlled processing resources. This pattern of brain activity may constitute an important neural signature of language dominance in bilinguals.

Bilingualism at the core of the brain. Structural differences between bilinguals and monolinguals revealed by subcortical shape analysis

“…Importantly to our current goals, fMRI studies specifically focused on bilingualism have tended to underscore the relevance of subcortical structures for managing two or more languages. In particular, different studies have reported increased activation of the caudate nucleus in language switching (Abutalebi et al 2007a;Crinion et al 2006;Garbin et al 2011;Wang et al 2007;Wang et al 2009). Also, there is evidence of recruitment of the putamen during demanding articulatory and motor control processes, generally observed in bilinguals (Abutalebi et al 2013;Klein et al 1994;Tettamanti et al 2005).…”

“Il piccolo principe est allé”: Processing of Language Switches in Auditory Sentence Comprehension

“…Although behaviorally there were no differences in relative language proficiency in the participants' first or second languages, results revealed that perceiving language switches from French (second language) to Italian (first) resulted in less activation of the left caudate and bilateral anterior cingulate cortices than perceiving language switches from Italian to French [Abutalebi et al (2007), their Fig. 4 (http://www.jneurosci.org/cgi/content/ full/27/50/13762/F4)].…”

“…Indeed, a number of functional imaging studies on productive language switching (e.g., Hernandez et al, 2001) have found activation in areas linked to cognitive control (among others the anterior cingulate cortex, dorsolateral prefrontal cortex, and basal ganglia). The study by Abutalebi et al (2007), which was published recently in The Journal of Neuroscience, is one of few studies to have investigated the comprehension of language switches that occurred in spoken sentences. Despite the value of this study, its explanation of the difference between regular and irregular language switches is debatable.…”

“…The study by Abutalebi et al (2007) represents an important step forward in bilingual research and may prove to have long-lasting implications for models of bilingual language switching and bilingual language comprehension. In particular, the finding that perception of language switches activates areas related to cognitive control suggests the existence of an "input switch" between a bilingual's languages, a concept that has hitherto received little support.…”

“…Furthermore, the hypothesis that irregular language switching may require a greater amount of phonological and syntactic processing is never sufficiently justified by the authors, and neither is the supposedly greater involvement of lexical-semantic processing for the regular switches. In fact, in addition to lexical-semantic and phonological/syntactic processing, the areas reported in Abutalebi et al (2007) have been found to be activated by numerous other cognitive processes (e.g., inferior frontal regions have been connected to almost all aspects of language processing as well as various non-language-related tasks (cf. Poldrack, 2006).…”