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Speech Perception, Production and Bilingualism
Cognitive Neuroscience of Auditory Perception and Attention
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Executive control in Bilingual contexts

Project coordinator: Albert Costa.

Project members: César Ávila, Francisco Barceló, Vicente Belloch, Francesca Branzi, J.Carlos Bustamante, Jordi Costa-Faidella, Ian FitzPatrick, Gabriele Garbin, Mireia Hernández, Clara Martin, Aina Rodríguez-Pujadas, Núria Sebastián, Kristof Strijkers, Noelia Ventura.
       

GOALS OF THE PROJECT 

The main objective of this project is to explore how specific mechanisms of bilingual control affect the functioning of the domain-general executive control system. To this end, we conduct experiments related to various aspects of the executive control system (i.e., task switching, conflict resolution, etc.). We make use of behavioral and neuroimaging techniques (ERPs and fMRI) in monolinguals and early highly proficient bilinguals.

 

SUBPROJECT 1:  Bilingual advantage in conflict processing: Monitoring vs. resolution processes. 

The question regarding the potential impact of bilingualism on executive control stems from the need of bilinguals to control their two languages during speech production. Since bilinguals have two word forms associated to the same concepts (e.g., perro-gos), they need to prevent interference from the unintended language every time they produce speech. Thus, one of the executive control processes most likely to be affected by bilingualism is the one brought into play when individuals are faced with competing and conflicting responses. Therefore, we should expect bilinguals to outperform monolinguals in non-linguistic conflict resolution tasks (see previous results by Bialystok’s team in children, middle-age and old age bilinguals). In this subproject we aim to characterize more accurately the bilingual advantage in executive control. In particular, we explored the contribution of conflict monitoring and conflict resolution processes to this bilingual advantage, by making use of flanker and numerical Stroop paradigms. The results of these experiments revealed that bilingualism mostly affects the speed with which participants perform the task overall, that is, both in conditions in which there is conflicting information (incongruent trials) and in conditions where there is no conflict (congruent trials; Figure 1). This overall speed effect was attributed to a more efficient conflict monitoring system. However, the effect of bilingualism on the conflict resolution processes, as reflected by the magnitude of the conflict effect (the difference between incongruent and congruent trials) was much less reliable. In view of these results we conclude that: a) the impact of bilingualism on conflict processing is detectable even in individuals that are at the peak of their attentional capabilities, and b) this effect is mostly due to a more efficient conflict monitoring system.

 
  

        

Figure 1. Participants’ performance in a version of the flanker task. Reaction times broken by group of participants and type of trial. Error bars represent standard errors.

SUBPROJECT 2: Neural basis of task-switching and its relationship with bilingualism.

Early and highly proficient bilinguals have the remarkable ability to switch from one language to the other very quickly, easily, and without interference. Does this extra training in switching affect the efficiency of domain-general switching processes? In this subproject, we investigated non-linguistic task switching in monolinguals and bilinguals using behavioural measures and fMRI. Participants were asked to classify cards depending on their colour (red versus blue) or their form (circle versus square). Each card was presented with a cue indicating which criterion had to be used (“COLOR” or “FORM”). Depending on the cue, participants had to classify a card using the same criterion as for the previous trial (non-switch trial) or to use the other criterion (switch trial). Participants were overall better and faster for non-switch than switch trials. Interestingly, the switching cost (switch trial RTs – non-switch trial RTs) was larger for monolinguals than bilinguals. Using fMRI, we explored the potential differences in the recruitment of brain circuits involved in this non-linguistic switching-task between bilinguals and monolinguals. Monolinguals activated the right inferior frontal gyrus, an area typically related to task switching. Early bilinguals, in contrast, activated the left inferior frontal gyrus (left IFG), an area related to language switching and processing (Figure 2). Our study showed striking differences in the cortical network involved in cognitive control between monolinguals and bilinguals. The fact that the left IFG has been consistently related to bilingual language control is suggestive of a certain degree of overlap between the cortical network responsible for language control and general-purpose non-linguistic cognitive control in the case of bilinguals but not in monolinguals.

    

Figure 2. (a) Schematic illustration of the sequence of a trial with sound (the 49 Hz tactile vibration present in the first interval). (b) Results for one participant. Tactile threshold improves with frequency (x axis) and is better with accompanying sounds (green and blue) than without (red).