Spanish Sign Language processing in hearing bimodal bilinguals: an fMRI study

Costello, B. . 1 , Villameriel, S. 1 , Paz-Alonso, P. 1 & Carreiras, M. . 1, 2, 3

2 Ikerbasque, Basque Foundation for Science

Previous neuroimaging evidence has shown that SL recruits a similar set of left-lateralized perisylvian regions to those engaged in spoken languages, including the inferior frontal gyrus (IFG). Various questions remain regarding the functional dynamics supporting SL processing: Does engagement of left-lateralized perisylvian regions during language processing differ as a function of modality? Is there a specific functional signature of SL processing? To what extent does language processing rely on different neural dynamics as a function of being a native versus a L2 signer?
We investigated these questions with an fMRI study with 23 native Spanish Sign Language (LSE)-Spanish bilinguals, 20 late LSE-Spanish bilinguals and 23 bilingual controls without LSE knowledge. Results confirmed that SL and spoken language recruited a similar set of left-perisylvian regions. Nevertheless, signers exhibited significant stronger regional engagement for SL processing than for spoken language processing across left-perisylvian nodes. Moreover, signers showed stronger activation in left IFG to process signs compared to sign-naïve controls. Furthermore, L2 signers showed involvement of the right parietal lobe relative to native signers (Fig. 1C). These results constitute the strongest evidence so far showing differential modality-specific neural dynamics involving SL processing in hearing bilinguals.