Journal Article

Sign and speech: amodal commonality in left hemisphere dominance for comprehension of sentences

Kuniyoshi L. Sakai, Yoshinori Tatsuno, Kei Suzuki, Harumi Kimura and Yasuhiro Ichida

in Brain

Published on behalf of The Guarantors of Brain

Volume 128, issue 6, pages 1407-1417
Published in print June 2005 | ISSN: 0006-8950
Published online February 2005 | e-ISSN: 1460-2156 | DOI: http://dx.doi.org/10.1093/brain/awh465
Sign and speech: amodal commonality in left hemisphere dominance for comprehension of sentences

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The neural basis of functional lateralization in language processing is a fundamental issue in systems neuroscience. We used functional MRI (fMRI) to examine hemispheric dominance during the processing of signed and spoken sentences. By using tasks involving comprehension of sentences (Sc) and sentential non-word detection (Sn), we compared different groups and stimulus conditions. Under the sign condition with sentence stimuli in Japanese Sign Language (JSL), we tested two groups of subjects: Deaf signers (Deaf) of JSL, and hearing bilinguals (children of Deaf adults, CODA) of JSL and Japanese (JPN). Under the speech condition, we tested hearing monolinguals (Mono) of JPN with auditory JPN stimuli alone (AUD), or with an audiovisual presentation of JPN and JSL stimuli (A&V). We found that the overall bilateral activation patterns under the four experimental conditions of Deaf, CODA, AUD and A&V were almost identical, despite differences in stimuli (JSL and JPN) and groups (Deaf, CODA and Mono). Moreover, consistently left-dominant activations involving frontal and temporo-parietal regions were observed across all four conditions. Furthermore, irrespective of the modalities of sign and speech, the main effects of task (Sc–Sn) were found primarily in the left regions: the ventral part of the inferior frontal gyrus (F3t/F3O), the precentral sulcus, the superior frontal gyrus, the middle temporal gyrus, the angular gyrus and the inferior parietal gyrus. Among these regions, only the left F3t/F3O showed no main effects of modality condition. These results demonstrate amodal commonality in the functional dominance of the left cortical regions for comprehension of sentences, as well as the essential and universal role of the left F3t/F3O in processing linguistic information from both signed and spoken sentences.

Keywords: deaf; sign language; speech; functional lateralization; frontal cortex; AG = angular gyrus; ASL = American Sign Language; AUD = auditory JPN stimuli alone; A&V = audiovisual presentation of JPN and JSL stimuli; BA = Brodmann area; BSL = British Sign Language; CODA = hearing bilinguals, children of Deaf adults; Deaf = Deaf signers; F1 = superior frontal gyrus; F2 = middle frontal gyrus; F3O = inferior frontal gyrus, orbital part; F3t = inferior frontal gyrus, triangular part; fMRI = functional MRI; IPG = inferior parietal gyrus; JPN = Japanese; JSL = Japanese Sign Language; L1 = first language; L2 = second language; Mono = hearing monolinguals; MTG = middle temporal gyrus; PrCS = precentral sulcus; R = repetition detection; Sc = comprehension of sentences; SMG = supramarginal gyrus; Sn = sentential non-word detection; STG = superior temporal gyrus

Journal Article.  6902 words.  Illustrated.

Subjects: Neurology ; Neuroscience

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