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fMRI of Speech and Sign Provides Evidence for a Core Modality-Independent Language Production Network
Poster Session B, Wednesday, September 30, 4:30 - 6:30 pm, Wangari Maathai
Idil Demircan1, Rabia Ergin2, Alexis Hervais-Adelman1,3; 1University of Geneva, 2Independent researcher, 3University of Zurich
Shadowing entails rapid overt repetition of an incoming linguistic signal, and has been used to investigate mechanisms of sensorimotor integration during production. Previous neuroimaging studies of speech shadowing have shown engagement of a bilateral perisylvian network spanning superior temporal, sensorimotor, and inferior frontal cortices, alongside subcortical and cerebellar activations (Peschke et al., 2009; Hervais-Adelman et al., 2015). While studies of speech shadowing have provided invaluable insights into auditory-motor integration, a similar neuroimaging paradigm has not, to our knowledge, been applied to sign languages, leaving open whether the sensorimotor network supporting shadowing is shared or different across language modalities. As part of a functional magnetic resonance imaging (fMRI) study of cross-modal simultaneous interpreting between Turkish and Turkish Sign Language (TİD) in Children of Deaf Adults (CODAs), we collected within-modality shadowing data to serve as a within-language control for the perception, production, and self-monitoring demands of simultaneous interpreting. We note with interest that these data also constitute the first within-subject bimodal comparison of speech and sign shadowing in early balanced bimodal bilinguals (N = 17, mean age = 27.7, SD = 8.6; mean AoA for TİD = 1.4 years, SD = 1.5; mean AoA for Turkish = 1.4 years, SD = 1.4). Participants were asked to complete the tasks of simultaneously interpreting, shadowing, and passively attending the sentences in each language. Here, we report shadowing relative to passive conditions in each modality, and a conjunction across the two to identify the neural underpinnings of sensorimotor integration across language production mechanisms. All reported results are cluster-level FWE-corrected p<.05 with cluster-forming threshold p<.001. Shadowing in Turkish (versus passive listening) recruited a bilateral perisylvian sensorimotor network, including rolandic operculum, supplementary motor area (SMA), cingulate, superior temporal cortex, and insula, alongside bilateral cerebellar engagement and subcortical recruitment of thalamus and basal ganglia. Shadowing in TİD (versus passive watching) recruited a more extensive bilateral motor network extending into superior frontal cortex, bilateral SMA, and bilateral cingulate, together with left supramarginal gyrus, right inferior frontal operculum, bilateral visual association cortex (lingual and cuneus), and bilateral cerebellar and thalamic engagement. A cross-modal conjunction analysis revealed a shared, modality-independent network for shadowing. This network comprised bilateral perisylvian cortex (rolandic operculum), medial premotor cortex (SMA and cingulate), left sensorimotor cortex, bilateral inferior frontal operculum, cerebellum, and thalamus. These regions have been previously associated with distinct individual functions: perisylvian cortex (rolandic operculum) in auditory-motor integration, medial premotor cortex (SMA and cingulate) in action sequencing and monitoring, sensorimotor cortex in sensorimotor control, inferior frontal operculum in articulatory planning, cerebellum in forward-model prediction and motor timing, and thalamus in sensorimotor relay. Furthermore, the activations observed in the conjunction analysis point towards a core network supporting motor planning, execution and self-monitoring demands of linguistic output, irrespective of language modality. Taken together, we suggest that modality-independent network revealed for shadowing across spoken and signed languages constitutes a core coordination network engaged by linguistic output, alongside sensory and articulator-specific engagement reflecting the distinct demands of each modality.
Topic Areas: Speech Motor Control, Signed Language and Gesture