Abstract
A prominent theory of bilingual speech production holds that appropriate language selection is achieved via inhibitory control. Such inhibition may operate on the whole-language and/or item-specific level. In this study, we examined these two levels of control in parallel, by introducing a novel element into the traditional cued language switching paradigm: half of the stimuli were univalent (each required naming in the same language every time it appeared), and the other half were bivalent (each required naming in different languages on different trials). Contrasting switch and stay trials provided an index for whole-language inhibition, while contrasting bivalent and univalent stimuli provided an index for item-specific inhibition. We then investigated the involvement of domain-general brain mechanisms in these two levels of language control. Neuroimaging studies report activation of the pre-supplementary motor area (pre-SMA), a key region in the executive control brain network, during language switching tasks. However, it is unclear whether or not the pre-SMA plays a causal role in language control, and at which level it exerts control. Using repetitive transcranial magnetic stimulation (TMS) to transiently disrupt the pre-SMA, we observed an essential role of this brain region in general speech execution, while evidence for its specific involvement in each level of inhibition remains inconclusive.
Highlights
At least half of the world’s population today is bilingual or multilingual [1]
Using the same picture-naming task as Experiment 1, we investigate these questions by perturbing the pre-supplementary motor area (pre-SMA) via a repetitive transcranial magnetic stimulation (TMS) protocol and observing the effect on whole-language and item-specific inhibition
The present findings suggest that pre-SMA perturbation may have affected valence cost
Summary
At least half of the world’s population today is bilingual or multilingual [1]. Knowing more than one language comes with the benefit of having access to information from a wider range of sources, as well as being able to communicate with more diverse groups of people. It demands some kind of control mechanism to keep the languages separate and to ensure they do not interfere with each other. An influential view was put forward by Green [2], in his “inhibitory control model” of bilingual speech production. How do bilingual individuals coordinate their two languages successfully, so that they can speak the desired language at any given time? According to this model, appropriate language control is achieved via inhibition of the non-target language. That is, when bilinguals speak one language, they need to suppress the other language to avoid interference. Based on the assumption that lexical items in the more dominant language have a higher level of baseline activation, Green proposes that stronger inhibition needs to be placed on that language in order to enable speech production in the non-dominant language
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