[Sign language, a Danish dialect?].
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Since sign language conveys many grammatical relations by manipulating spatial relations, its study provides a unique opportunity to investigate cerebral specialization for language. Three deaf signers with damage to the left hemisphere were administered an array of formal sign language tests and a linguistic analysis of their spontaneous signing was performed. All three signers showed aphasia for sign language. Strikingly, in these patients, differential damage within the left hemisphere appeared to lead to selective impairment of the structural layers of sign language (e.g. lexicon versus grammar). These data provide the first demonstration of grammatical breakdown in sign language. Importantly, the language impairments of these patients stood in marked contrast to their relatively intact capacities to process nonlanguage visual-spatial relationships. These results suggest that the two cerebral hemispheres of deaf signers can develop separate specializations for linguistic and for visual-spatial processing, even for a visual-spatial language. They further suggest that the left hemisphere has an innate predisposition for language.
Since signed languages utilize visual-gestural channels, their study allows a unique opportunity for insight into the ways language and gesture may be represented in the brain. The separability of apraxia and aphasia for sign language was examined in four deaf signers who had unilateral brain damage, three to the left hemisphere and one to the right hemisphere. These patients were administered various tests for apraxia and a test of pantomime recognition. The patient with damage to the right hemisphere was not apraxic as we would expect. For the patients with damage to the left hemisphere, all of whom were aphasic for sign language, strong dissociations emerged between their capacities for sign language and their nonlinguistic motor skills. The language deficits of these patients seemed related to specific linguistic components of sign language rather than to an underlying motor disorder or an underlying disorder in the capacity to express and comprehend symbols of any kind. This separation between linguistic and nonlinguistic function is all the more striking, because sign language and gesture are transmitted in the same modality.
Unlike spoken languages, sign languages of the deaf make use of two primary articulators, the right and left hands, to produce signs. This situation has no obvious parallel in spoken languages, in which speech articulation is carried out by symmetrical unitary midline vocal structures. This arrangement affords a unique opportunity to examine the robustness of linguistic systems that underlie language production in the face of contrasting articulatory demands and to chart the differential effects of handedness for highly skilled movements. Positron emission tomography (PET) technique was used to examine brain activation in 16 deaf users of American Sign Language (ASL) while subjects generated verb signs independently with their right dominant and left nondominant hands (compared to the repetition of noun signs). Nearly identical patterns of left inferior frontal and right cerebellum activity were observed. This pattern of activation during signing is consistent with patterns that have been reported for spoken languages including evidence for specializations of inferior frontal regions related to lexical-semantic processing, search and retrieval, and phonological encoding. These results indicate that lexical-semantic processing in production relies upon left-hemisphere regions regardless of the modality in which a language is realized, and that this left-hemisphere activation is stable, even in the face of conflicting articulatory demands. In addition, these data provide evidence for the role of the right posterolateral cerebellum in linguistic-cognitive processing and evidence of a left ventral fusiform contribution to sign language processing.
In humans the two cerebral hemispheres of the brain are functionally specialized with the left hemisphere predominantly mediating language skills. The basis of this lateralization has been proposed to be differential localization of the linguistic, the motoric, or the symbolic properties of language. To distinguish among these possibilities, lateralization of spoken language, signed language, and nonlinguistic gesture have been compared in deaf and hearing individuals. This analysis, plus additional clinical findings, support a linguistic basis of left hemisphere specialization.
Congenitally deaf individuals, interpreters for the deaf and hearing controls viewed words, dots, American sign language signs and drawings of objects presented tachistoscopically. The stimuli were presented both bilaterally and unilaterally to the subjects. The deaf subjects showed a significant left visual field (LVF) superiority for the processing of the drawings while the nondeaf groups showed significant right visual field (RVF) advantages. Laterality differences between groups on the other tasks were nonsignificant. The deaf group also showed a significant LVF advantage in the bilateral condition across all tasks as opposed to a RVF advantage yielded by nondeaf groups. A significant LVF advantage for words and dots was found compared to the RVF advantage for signs across all subjects. The differences between deaf and nondeaf groups are discussed in terms of processing strategies and the critical period for language acquisition theory.
This paper traces the development of a new technology, the Interactive Video-Questionnaire, for interviewing Deaf persons by using manually signed questionnaires. After encountering numerous obstacles to conducting surveys with Deaf persons about substance abuse using the same methods typically used with hearing persons, the researchers, with a Small Business Innovative Research grant from the National Institute on Drug Abuse, piloted a survey method that uses videodisc and bar code readers to present survey questions signed on screen in American Sign Language and Signed English. Following consultations with Deaf participants, deficiencies of this method were identified and corrected. An interactive multimedia program was created in Phase II of this research effort that offered questions visually in American Sign Language, Signed English, or Speechreading. All questions were subtitled in written English, with Touchscreen entry and automatic data capture and storage. The potential exists for many important uses of the Interactive Video-Questionnaire.
As language is such a fundamental tool in the determination of a diagnosis and in patient education, non-English-speaking patients and deaf patients often suffer from inferior medical care. Deaf adults and adults studying English as a second language (third- to fifth-grade English-comprehension level) were compared. Participants completed a survey and a test of commonly used medical vocabulary. The two populations did not differ significantly in education level or in vocabulary test scores. Deaf patients were often less able to speak to their physician in their customary language (sign language); as a result, they perceive greater difficulties in expressing themselves to their physicians and reexplain themselves less frequently in response to misunderstandings. It is clear that deaf patients should be recognized as a subset of non-English-speaking patients who are at increased risk for poor physician-patient communication.
Hearing impairment in children is considered in its various aspects: medical, sociological, psychological, and educational. After a review of the aetiologies, the biological consequences of early auditory deprivation are underlined. The necessity of avoiding or reducing them justifies the efforts made to insure early diagnosis and adequate intervention. Screening and diagnostic techniques are described and illustrated by current results. The particular features of deafness, which stands out among other physical handicaps by the fact that it has given birth to a language, sign language, are stressed and the resulting socio-cultural implications are described. The relationships between deafness and psychology are treated so as to point out that there are no psychological features which characterize deafness, but that it can lead to several cognitive and behavioural consequences. The multiple interventions requested by a child's hearing impairment are detailed, emphasizing that medical or surgical actions must be part of a team work. The physician is called upon to play an essential part in this work, which he can correctly fulfill only by taking into account the sociological, cultural, psychological, educational and prosthetic aspects. The principles of prosthetic adaptation and the different types of prosthetic devices are presented, with special mention of recent and prospective developments. After a historical survey of deaf education, the evolution of ideas and methods from 1972 to 1987 is related, and the presently utilized methods are described and discussed. The different educational structures and their respective merits are outlined, as well as the action in favour of deaf children and their families of social services and parental cooperation.
We consider the earliest stages of language acquisition in both vocal and gestural modalities. The basic hypothesis is that there is a kind of equipotentiality between the two modalities and that the choice between the two depends on the linguistic input to which the child is exposed. We set forth the results of studies conducted in deaf and hearing children who acquire as native language the sign language used by deaf persons (gestural modality) and discuss the data on language acquisition in hearing and deaf children exposed to the American Sign Language (ASL) and in deaf children exposed to the Italian Sign Language (LIS). We go on to present the results of work in deaf children exposed to a bimodal Italian input. Against the background of studies in hearing children exposed to spoken Italian only we discuss the role of the gestural modality in the language acquisition of these children from the holophrastic to the diphrastic period. The comparison of sign language acquisition and spoken language acquisition will enable us to assess which aspects may be considered universal and which modality-related.
Virtually all right-handed individuals are left hemisphere dominant for language. Sign languages of the deaf provide an unusual vehicle for exploring the link between handedness and hemispheric specialization for language since in sign language the hands themselves are the language articulators. Performance of the right and left hand was examined in deaf native users of American Sign Language (ASL) for speeded production of one-handed signs and for shadowing of signed discourse. Opposite patterns of asymmetries in hand performance were found in right- and left-handers. However, left-handers were more flexible than right-handers in signing with their non-preferred hand. Furthermore, unusual patterns of hand use for sign were found in a deaf signer with a left hemisphere lesion, possibly indexing increased mediation of the intact hemisphere. Implications for brain organization of language in a visual-gestural mode are discussed.
Visual abilities in deaf individuals may be altered as a result of auditory deprivation and/or because the deaf rely heavily on a sign language (American Sign Language, or ASL). In this study, we asked whether attentional abilities of deaf subjects are altered. Using a direction of motion discrimination task in the periphery, we investigated three aspects of spatial attention: orienting of attention, divided attention, and selective attention. To separate influences of auditory deprivation and sign language experience, we compared three subject groups: deaf and hearing native signers of ASL and hearing nonsigners. To investigate the ability to orient attention, we compared motion thresholds obtained with and without a valid spatial precue, with the notion that subjects orient to the stimulus prior to its appearance when a precue is presented. Results suggest a slight advantage for deaf subjects in the ability to orient spatial attention. To investigate divided attention, we compared motion thresholds obtained when a single motion target was presented to thresholds obtained when the motion target was presented among confusable distractors. The effect of adding distractors was found to be identical across subject groups, suggesting that attentional capacity is not altered in deaf subjects. Finally, to investigate selective attention, we compared performance for a single, cued motion target with that of a cued motion target presented among distractors. Here, deaf, but not hearing, subjects performed better when the motion target was presented among distractors than when it was presented alone, suggesting that deaf subjects are more affected by the presence of distractors. In sum, our results suggest that attentional orienting and selective attention are altered in the deaf and that these effects are most likely due to auditory deprivation as opposed to sign language experience.
Transcribing sign communication used simultaneously with spoken English presents investigators with a unique problem: the singular quality of the bimodal communicative interactions cannot be accurately depicted using accepted conventions for recording either spoken or signed language samples. This article proposes guidelines for transcribing such data. The need for guidelines arose during an earlier study of the language development of a hearing child of deaf parents. To meet the immediate needs of that study, rules and conventions from previous studies were combined with newly generated ones, resulting in the guidelines proposed in this article. The guidelines can be applied to data in which intermodal linguistic influence is suspected.
Recently, we reported a strong right visual field/left hemisphere advantage for motion processing in deaf signers and a slight reverse asymmetry in hearing nonsigners (Bosworth & Dobkins, 1999). This visual field asymmetry in deaf signers may be due to auditory deprivation or to experience with a visual-manual language, American Sign Language (ASL). In order to separate these two possible sources, in this study we added a third group, hearing native signers, who have normal hearing and have learned ASL from their deaf parents. As in our previous study, subjects performed a direction-of-motion discrimination task at different locations across the visual field. In addition to investigating differences in left vs right visual field asymmetries across subject groups, we also asked whether performance differences exist for superior vs inferior visual fields and peripheral vs central visual fields. Replicating our previous study, a robust right visual field advantage was observed in deaf signers, but not in hearing nonsigners. Like deaf signers, hearing signers also exhibited a strong right visual field advantage, suggesting that this effect is related to experience with sign language. These results suggest that perceptual processes required for the acquisition and comprehension of language (motion processing in the case of ASL) are recruited by the left, language-dominant, hemisphere. Deaf subjects also exhibited an inferior visual field advantage that was significantly larger than that observed in either hearing group. In addition, there was a trend for deaf subjects to perform relatively better on peripheral than on central stimuli, while both hearing groups showed the reverse pattern. Because deaf signers differed from hearing signers and nonsigners along these domains, the inferior and peripheral visual field advantages observed in deaf subjects is presumably related to auditory deprivation. Finally, these visual field asymmetries were not modulated by attention for any subject group, suggesting they are a result of sensory, and not attentional, factors.
Most deaf children are born to hearing parents. Yet, many hearing parents are unable to communicate clearly and unambiguously with their deaf offspring. This study looked at changes in the number of parents of deaf offspring who learn sign language, and the signing skills of those parents. It found that over the years the signing skills of these parents have been improving. Of the younger deaf offspring in this study, 73% reported that their parents knew some sign language. Younger offspring rated their parents' signing skills higher than did older offspring. These results may indicate that more parents are now learning sign language.
The intracarotid amobarbital procedure (IAP) was conducted with a profoundly deaf young man prior to right anteromedial temporal lobectomy for pharmacologically refractory partial complex seizures. The IAP required considerable modification in order to take into account the use of varying sign language methods and related issues. Visual memory, American Sign Language, signed English, and finger-spelling functioning were all assessed. The patient manifested left hemisphere dominance for all these abilities, performing well under right hemisphere anesthesia. In contrast, no ability to function on these tasks was detectable when the left hemisphere was anesthetized. This demonstrates that an intact left temporal lobe and related structures are sufficient to support sign language functioning. The development of a deaf adaptation of the IAP is of methodological significance, as the IAP is thereby rendered accessible for deaf patients.