Abstract
The neurobiology of sentence comprehension is well-studied but the properties and characteristics of sentence processing networks remain unclear and highly debated. Sign languages (i.e., visual-manual languages), like spoken languages, have complex grammatical structures and thus can provide valuable insights into the specificity and function of brain regions supporting sentence comprehension. The present study aims to characterize how these well-studied spoken language networks can adapt in adults to be responsive to sign language sentences, which contain combinatorial semantic and syntactic visual-spatial linguistic information. Twenty native English-speaking undergraduates who had completed introductory American Sign Language (ASL) courses viewed videos of the following conditions during fMRI acquisition: signed sentences, signed word lists, English sentences and English word lists. Overall our results indicate that native language (L1) sentence processing resources are responsive to ASL sentence structures in late L2 learners, but that certain L1 sentence processing regions respond differently to L2 ASL sentences, likely due to the nature of their contribution to language comprehension. For example, L1 sentence regions in Broca's area were significantly more responsive to L2 than L1 sentences, supporting the hypothesis that Broca's area contributes to sentence comprehension as a cognitive resource when increased processing is required. Anterior temporal L1 sentence regions were sensitive to L2 ASL sentence structure, but demonstrated no significant differences in activation to L1 than L2, suggesting its contribution to sentence processing is modality-independent. Posterior superior temporal L1 sentence regions also responded to ASL sentence structure but were more activated by English than ASL sentences. An exploratory analysis of the neural correlates of L2 ASL proficiency indicates that ASL proficiency is positively correlated with increased activations in response to ASL sentences in L1 sentence processing regions. Overall these results suggest that well-established fronto-temporal spoken language networks involved in sentence processing exhibit functional plasticity with late L2 ASL exposure, and thus are adaptable to syntactic structures widely different than those in an individual's native language. Our findings also provide valuable insights into the unique contributions of the inferior frontal and superior temporal regions that are frequently implicated in sentence comprehension but whose exact roles remain highly debated.
Highlights
The neurobiology of sentence comprehension has been extensively studied for decades
For English sentences, widespread significant activations were identified in the right middle frontal gyrus (MFG), right angular gyrus (AG), bilateral precentral gyrus (PrCG), inferior frontal gyri (IFG, predominately in the pars opercularis), superior temporal gyrus (STG), middle temporal gyrus (MTG), intraparietal sulcus (IPS), lingual gyrus, inferior occipital gyrus (IOG), middle occipital gyrus (MOG), fusiform gyrus, calcarine sulcus, and supplementary motor area (SMA)
In the English word list condition, significant activations were found in the bilateral inferior frontal gyrus (IFG), precentral gyrus, MFG, IOG, MOG, lingual gyrus, fusiform gyrus, and SMA superior parietal lobule (SPL), right MTG, AG, and insula (Figure 2B, Table 1)
Summary
The neurobiology of sentence comprehension has been extensively studied for decades. Yet, there remains intense debate regarding the nature and specificity of contributions to sentence comprehension of several left fronto-temporal brain regions. This work has identified a left-lateralized frontotemporo-parietal network that is activated by the presence of sentence structures, compared to a variety of acoustic controls, with the most common regions of interest in Broca’s area (posterior 2/3 of the left inferior frontal gyrus), the posterior superior temporal gyrus, and anterior temporal cortex (Dronkers et al, 2004; Hickok and Poeppel, 2007; Magnusdottir et al, 2013). These regions are frequently identified in studies of sentence comprehension, their respective contributions remain controversial. Posterior superior temporal regions have been implicated by many of these same studies in combinatorial semantics, syntax and prosody (Humphries et al, 2006; Griffiths et al, 2013; Wilson et al, 2014), as well as in lexical and phonological processing (Damasio et al, 2004; Hickok and Poeppel, 2007; Graves et al, 2008)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have