Polish Sign Language comprehension: effects of modality and proficiency. An fMRI study of hearing late-learners and deaf users

Banaszkiewicz, A. 1 , Matuszewski, J. 1 , Bola, ?. 1, 2 , Szczepanik, M. 1 , Rutkowski, P. . 3 , Szwed, M. 2 , Emmorey, K. 4 , Jednoróg, K. . 5 & Marchewka, A. 1

1 Laboratory of Brain Imaging, Neurobiology Center, Nencki Institute of Experimental Biology, Polish Academy of Sciences, Warsaw, Poland
2 Institute of Psychology, Jagiellonian University, Kraków, Poland
3 Section for Sign Linguistics, Faculty of Polish Studies, University of Warsaw, Warsaw, Poland
4 Laboratory for Language and Cognitive Neuroscience, San Diego State University, San Diego, USA
5 Laboratory of Psychophysiology, Nencki Institute of Experimental Biology, Polish Academy of Sciences, Warsaw, Poland

Previous fMRI studies comparing spoken audio-visual (AV) and sign languages (SL) have identified modality-independent (fronto-temporal) and modality-dependent (occipito-parietal for SL and auditory for AV) language systems. However, these findings were based on comparisons between native users of both languages - little is known, how these networks develop in hearing late-learners (HLL) of SL.
In Experiment 1, HLL group (N=21) performed lexical and sentential tasks in Polish Sign Language (PJM) and AV Polish after a 8 months-long PJM course. Modality-independent activations (conjunction of PJM and AV) were located in bilateral inferior frontal and superior/middle temporal gyri, while modality dependent clusters were found in occipito-parietal (PJM>AV) and superior temporal (AV>PJM) regions. In Experiment 2, HLL brain activity was compared to deaf users of SL (N=14), to investigate differences between novel and native SL processing networks. Similarities in activation during comprehension of signs and sentences were present, however, HLL recruited superior parietal lobule (SPL) to a greater extent. Additionally, we observed cross-modal activation in secondary auditory region (STG) in deaf subjects. Our study shows modality-dependent and modality-independent language systems, engaged also in non-proficient hearing individuals. Moreover, HLL rely more on SPL (involved in spatial properties of signed material) than native deaf individuals.