EEG analysis of Brazilian sign language comprehension

Abstract

LIM 01, HCFMUSP, Sa˜o Paulo, BrazilSign languages result from the effort of the deaf community todiscover and create ways to communicate and they reach the com-plexity of any other spoken language, which includes: phonology,morphology, syntax; semantic and pragmatic fields. Phonology dividesthe minimal distinctive units of each arm, hand, and face movement.Morphology can be applied to create many different words from thesame radical. Syntax defines the word gesture positions of all thesymbols into the phrase. Word meanings are correlated with the ges-ture movements, but these movements are far from being just mimics.They have their own abstractions and can create a large semantic field.As any other language, the sign language depends on the effect createdby the gestures so the signer could evaluate their practical meaningsand power of expression.ASL is a very well known sign language, and neuroscience hasshown that most of the neural areas involved with oral languages pro-duction and comprehension are also involved in ASL processing. TheBrazilian Signed Language (Libras) is gaining importance in the Bra-zilian deaf community. Its first dictionary was recently published, butnothing is known about its brain processing. The present paper inves-tigated the brain activity associated with the comprehension of signedcharadesandstoriesbyagroupofBraziliandeafpeoplethatusesLibrasas their first language. The EEG methodology used here is the sameemployed by our group to study charade and story comprehension inoral languages (Foz, et al., Pediatric Neurology, 2002/26: 106–115).The most peculiar fact in the present results is the common en-rollment of neurons at parietal-medial (PZ), central (C3, C4), andfrontal (F3, F4) bilateral areas in Libras decoding. Frontal verbalareas (F7, FP1, F3) and left temporal areas (T3, T5) are also in-volved with the linguistic processing. The visual stimulus created bythe signal languages comprehend facial expression, hand shape andmovement, and the relative position of the hand in respect to thebody. The activation of the central and parietal areas of the lefthemisphere may be involved with the hand shape processing. It isnear Wernicke’s area, whose neurons are in charge of accessing thesemantics of the words. Also, the hand parietal area makes connec-tions with pre-motor cortex, and probably with Broca’s area. Theposition of the hands in relation to the body is also processed byneurons in the parietal areas, whereas hand movements are processedby neurons at temporal medial areas.The results show some similarities between Libras and oral lan-guages processing such as the involvement of the oral language areas atfrontal and temporal sites. But they also show the activation of centralandparietalareasprobablyinvolvedinmotionprocessingofhandsandarms and the activation of widely right brain areas may be involved insome visual representation of the signs and the spatial reference used insign languages. These results seem also to point to a common neuralprocessing for both Libras and ASL, which may indicate a particularneural structure for sign language comprehension.Brain and Language 87 (2003) 193www.elsevier.com/locate/b&l0093-934X/$ - see front matter 2003 Elsevier Science (USA). All rights reserved.doi:10.1016/S0093-934X(03)00266-9