title: Examining the contribution of motor movement and language dominance to increased left lateralization during sign generation in native signers.
abstract: The neural systems supporting speech and sign processing are very similar, although not identical. In a previous fTCD study of hearing native signers (Gutierrez-Sigut, Daws, et al., 2015) we found stronger left lateralization for sign than speech. Given that this increased lateralization could not be explained by hand movement alone, the contribution of motor movement versus 'linguistic' processes to the strength of hemispheric lateralization during sign production remains unclear. Here we directly contrast lateralization strength of covert versus overt signing during phonological and semantic fluency tasks. To address the possibility that hearing native signers' elevated lateralization indices (LIs) were due to performing a task in their less dominant language, here we test deaf native signers, whose dominant language is British Sign Language (BSL). Signers were more strongly left lateralized for overt than covert sign generation. However, the strength of lateralization was not correlated with the amount of time producing movements of the right hand. Comparisons with previous data from hearing native English speakers suggest stronger laterality indices for sign than speech in both covert and overt tasks. This increased left lateralization may be driven by specific properties of sign production such as the increased use of self-monitoring mechanisms or the nature of phonological encoding of signs.
authors.affiliation: Deafness, Cognition & Language Research Centre, University College London, United Kingdom; Departamento de Metodología de las Ciencias del Comportamiento, Universitat de València, Spain. Electronic address: eva.gutierrez@ucl.ac.uk.
authors.forename: Eva
authors.initials: E
authors.lastname: Gutierrez-Sigut
authors.affiliation: Deafness, Cognition & Language Research Centre, University College London, United Kingdom; Institute of Cognitive Neuroscience, University College London, United Kingdom. Electronic address: h.payne@ucl.ac.uk.
authors.forename: Heather
authors.initials: H
authors.lastname: Payne
authors.affiliation: Deafness, Cognition & Language Research Centre, University College London, United Kingdom; Institute of Cognitive Neuroscience, University College London, United Kingdom. Electronic address: m.macsweeney@ucl.ac.uk.
authors.forename: Mairéad
authors.initials: M
authors.lastname: MacSweeney
mesh_terms: D000293:Adolescent; D000328:Adult; D003638:Deafness / Q000503:physiopathology; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006225:Hand / Q000502:physiology; D006309:Hearing / Q000502:physiology; D006801:Humans; D007802:Language; D008037:Linguistics; D008297:Male; D009068:Movement / Q000502:physiology*; D012660:Semantics; D012813:Sign Language; D013060:Speech / Q000502:physiology; D013997:Time Factors; D055815:Young Adult
keywords: Language lateralization; Overt language production; Phonological fluency; Semantic fluency; Sign language; fTCD