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PubMed2004

The neurology of sign language.

Forms of sign language have developed in a number of countries. American Sign Language, which originated from French signing, has been most extensively researched. As sign language is based on gestures executed in space and perceived visually it might be thought that it would mainly be a function of the right cerebral hemisphere when this is the non-dominant one. A number of studies are reviewed showing that sign language is a language in its own right and therefore, as with spoken language, its primary site of organization is in the dominant hemisphere. This does not mean that there is not a significant contribution from the other hemisphere with an interplay between the two. Each research project usually contributes some facet of knowledge apart from the main conclusions. These included the importance of distinguishing signs from gestures, the localization of different types of signing within the left dominant cerebral hemisphere, the fact that lesions of the right non-dominant hemisphere, although not causing a loss of signing will result in dyspraxia, and that aphasic symptoms of signing and speech are not modality dependant but reflected a disruption of language processes common to all languages. Examples are given of discoveries made by the use of the newer neuroradiological techniques such as functional magnetic resonance imaging and positron emission tomography, and no doubt these will lead to further advances in knowledge. The use of sign language in the treatment of patients with verbal aphasia is considered, especially of children with the Landau-Kleffner syndrome, but therapy of this kind can be used in children with delayed language development, and in other types of acquired aphasia at any age. Other methods of treatment than signing, such as cochlear implants may be increasingly used in the future, but it seems likely that sign language will continue to be a dominant feature in the deaf culture.

Aphasia↗
PubMed2005

Arabic sign language: a perspective.

Sign language in the Arab World has been recently recognized and documented. Many efforts have been made to establish the sign language used in individual countries, including Jordan, Egypt, Libya, and the Gulf States, by trying to standardize the language and spread it among members of the Deaf community and those concerned. Such efforts produced many sign languages, almost as many as Arabic-speaking countries, yet with the same sign alphabets. This article gives a tentative account of some sign languages in Arabic through reference to their possible evolution, which is believed to be affected by the diglossic situation in Arabic, and by comparing some aspects of certain sign languages (Jordanian, Palestinian, Egyptian, Kuwaiti, and Libyan) for which issues such as primes, configuration, and movement in addition to other linguistic features are discussed. A contrastive account that depicts the principal differences among Arabic sign languages in general and the spoken language is given.

Arab World↗
PubMed1993

Electromyographic study of overuse syndromes in sign language interpreters.

Sign language is the fourth most common language in the United States; this mode of communication involves sustained, repetitive use of the hand, wrist, and arm. Signers, therefore, are at risk of overuse disorders as carpal tunnel syndrome (CTS) and ulnar neuritis (UL). Using electrodiagnostic methods, the prevalence of hand nerve entrapments in signers was investigated. Thirty-three signers, six of whom were deaf, were compared to 21 age-matched controls (mean age = 31 and 29 years; respectively). Demographics were obtained by questionnaire. Physical examination and nerve conduction studies followed; 78 hands were examined. No significant mean differences in median motor or sensory latencies discriminated signers from controls. Although no signer's median SNAP latency was greater than 2 SDs from controls, some signers could be considered "abnormal" by other published criteria (eg, median/ulnar mid-palmer comparisons). Using these, 10 of 33 signers had mild abnormalities, five suggestive of CTS, three of UL, and two of both; of controls, two had CTS and two UL. The ratio of electrodiagnostic abnormalities did not differentiate the two groups (p > .05). Reports of hand and/or wrist pain were extremely high in interpreters (nondeaf signers) and were linked to EMG findings (p < .05). Deaf signers, even those with ED findings consistent with CTS, all reported no symptoms, possibly because their signing is less stressful or learned at an earlier age.

Carpal Tunnel Syndrome↗
PubMed1993

Processing a dynamic visual-spatial language: psycholinguistic studies of American Sign Language.

American Sign Language (ASL) has evolved within a completely different biological medium, using the hands and face rather than the vocal tract and perceived by eye rather than by ear. The research reviewed in this article addresses the consequences of this different modality for language processing, linguistic structure, and spatial cognition. Language modality appears to affect aspects of lexical recognition and the nature of the grammatical form used for reference. Select aspects of nonlinguistic spatial cognition (visual imagery and face discrimination) appear to be enhanced in deaf and hearing ASL signers. It is hypothesized that this enhancement is due to experience with a visual-spatial language and is tied to specific linguistic processing requirements (interpretation of grammatical facial expression, perspective transformations, and the use of topographic classifiers). In addition, adult deaf signers differ in the age at which they were first exposed to ASL during childhood. The effect of late acquisition of language on linguistic processing is investigated in several studies. The results show selective effects of late exposure to ASL on language processing, independent of grammatical knowledge.

Age Factors↗
PubMed2004

Baby hands that move to the rhythm of language: hearing babies acquiring sign languages babble silently on the hands.

The "ba, ba, ba" sound universal to babies' babbling around 7 months captures scientific attention because it provides insights into the mechanisms underlying language acquisition and vestiges of its evolutionary origins. Yet the prevailing mystery is what is the biological basis of babbling, with one hypothesis being that it is a non-linguistic motoric activity driven largely by the baby's emerging control over the mouth and jaw, and another being that it is a linguistic activity reflecting the babies' early sensitivity to specific phonetic-syllabic patterns. Two groups of hearing babies were studied over time (ages 6, 10, and 12 months), equal in all developmental respects except for the modality of language input (mouth versus hand): three hearing babies acquiring spoken language (group 1: "speech-exposed") and a rare group of three hearing babies acquiring sign language only, not speech (group 2: "sign-exposed"). Despite this latter group's exposure to sign, the motoric hypothesis would predict similar hand activity to that seen in speech-exposed hearing babies because language acquisition in sign-exposed babies does not involve the mouth. Using innovative quantitative Optotrak 3-D motion-tracking technology, applied here for the first time to study infant language acquisition, we obtained physical measurements similar to a speech spectrogram, but for the hands. Here we discovered that the specific rhythmic frequencies of the hands of the sign-exposed hearing babies differed depending on whether they were producing linguistic activity, which they produced at a low frequency of approximately 1 Hz, versus non-linguistic activity, which they produced at a higher frequency of approximately 2.5 Hz - the identical class of hand activity that the speech-exposed hearing babies produced nearly exclusively. Surprisingly, without benefit of the mouth, hearing sign-exposed babies alone babbled systematically on their hands. We conclude that babbling is fundamentally a linguistic activity and explain why the differentiation between linguistic and non-linguistic hand activity in a single manual modality (one distinct from the human mouth) could only have resulted if all babies are born with a sensitivity to specific rhythmic patterns at the heart of human language and the capacity to use them.

Hand↗
PubMed2002

Neural correlates of British sign language comprehension: spatial processing demands of topographic language.

In all signed languages used by deaf people, signs are executed in "sign space" in front of the body. Some signed sentences use this space to map detailed "real-world" spatial relationships directly. Such sentences can be considered to exploit sign space "topographically." Using functional magnetic resonance imaging, we explored the extent to which increasing the topographic processing demands of signed sentences was reflected in the differential recruitment of brain regions in deaf and hearing native signers of the British Sign Language. When BSL signers performed a sentence anomaly judgement task, the occipito-temporal junction was activated bilaterally to a greater extent for topographic than nontopographic processing. The differential role of movement in the processing of the two sentence types may account for this finding. In addition, enhanced activation was observed in the left inferior and superior parietal lobules during processing of topographic BSL sentences. We argue that the left parietal lobe is specifically involved in processing the precise configuration and location of hands in space to represent objects, agents, and actions. Importantly, no differences in these regions were observed when hearing people heard and saw English translations of these sentences. Despite the high degree of similarity in the neural systems underlying signed and spoken languages, exploring the linguistic features which are unique to each of these broadens our understanding of the systems involved in language comprehension.

Adolescent↗
PubMed2004

Children creating core properties of language: evidence from an emerging sign language in Nicaragua.

A new sign language has been created by deaf Nicaraguans over the past 25 years, providing an opportunity to observe the inception of universal hallmarks of language. We found that in their initial creation of the language, children analyzed complex events into basic elements and sequenced these elements into hierarchically structured expressions according to principles not observed in gestures accompanying speech in the surrounding language. Successive cohorts of learners extended this procedure, transforming Nicaraguan signing from its early gestural form into a linguistic system. We propose that this early segmentation and recombination reflect mechanisms with which children learn, and thereby perpetuate, language. Thus, children naturally possess learning abilities capable of giving language its fundamental structure.

Adolescent↗
PubMed1993

First-language acquisition after childhood differs from second-language acquisition: the case of American Sign Language.

This study determined whether the long-range outcome of first-language acquisition, when the learning begins after early childhood, is similar to that of second-language acquisition. Subjects were 36 deaf adults who had contrasting histories of spoken and sign language acquisition. Twenty-seven subjects were born deaf and began to acquire American Sign Language (ASL) as a first language at ages ranging from infancy to late childhood. Nine other subjects were born with normal hearing, which they lost in late childhood; they subsequently acquired ASL as a second language (because they had acquired spoken English as a first language in early childhood). ASL sentence processing was measured by recall of long and complex sentences and short-term memory for signed digits. Subjects who acquired ASL as a second language after childhood outperformed those who acquired it as a first language at exactly the same age. In addition, the performance of the subjects who acquired ASL as a first language declined in association with increasing age of acquisition. Effects were most apparent for sentence processing skills related to lexical identification, grammatical acceptability, and memory for sentence meaning. No effects were found for skills related to fine-motor production and pattern segmentation.

Adolescent↗
PubMed1996

Hemispheric specialization for sign language.

Most studies on sign lateralization provide inconclusive results about the role of the two hemispheres in sign language processing, whereas the cases reported in the clinical literature show sign language impairment only following left hemisphere damage, suggesting a similar neural organization to spoken languages. By discriminating different levels of processing, a tachistoscopic study found that in deaf subjects matches of sign language handshapes based on equivalence of meaning are processed faster in the right visual field, thus demonstrating a left hemisphere superiority.

Adolescent↗
PubMed2004

Neural correlates of working memory for sign language.

Eight, early bilingual, sign language interpreters participated in a PET study, which compared working memory for Swedish Sign Language (SSL) with working memory for audiovisual Swedish speech. The interaction between language modality and memory task was manipulated in a within-subjects design. Overall, the results show a previously undocumented, language modality-specific working memory neural architecture for SSL, which relies on a network of bilateral temporal, bilateral parietal and left premotor activation. In addition, differential activation in the right cerebellum was found for the two language modalities. Similarities across language modality are found in Broca's area for all tasks and in the anterior left inferior frontal lobe for semantic retrieval. The bilateral parietal activation pattern for sign language bears similarity to neural activity during, e.g., nonverbal visuospatial tasks, and it is argued that this may reflect generation of a virtual spatial array. Aspects of the data suggesting an age of acquisition effect are also considered. Furthermore, it is discussed why the pattern of parietal activation cannot be explained by factors relating to perception, production or recoding of signs, or to task difficulty. The results are generally compatible with Wilson's [Psychon. Bull. Rev. 8 (2001) 44] account of working memory.

Adult↗
PubMed2001

Sign language in childhood epileptic aphasia (Landau-Kleffner syndrome).

Acquired epileptic aphasia (AEA, or Landau-Kleffner syndrome) is a unique condition in which children can lose oral language (OL) comprehension and expression for a prolonged period. These children can benefit from visual forms of language, mainly sign language (SL), but the quality of SL has never been analyzed. The case is reported here of a boy with AEA who lost speech comprehension and expression from 3 years 6 months to 7 years and was educated in SL from the age of 6 years. His SL was evaluated at the age of 13 years and 6 months and compared with a control child with congenital sensorineural deafness. It was found that: (1) our patient achieved the same proficiency in SL as the control child with deafness; (2) SL learning did not compete with, but perhaps even hastened, the recovery of OL. Intact ability to learn a new linguistic code such as SL suggests that higher-order language areas were preserved and received input from a separate visual route, as shown by neuropsychological and functional imaging research in deaf and hearing signers.

Adolescent↗
PubMed2004

The neural correlates of spatial language in English and American Sign Language: a PET study with hearing bilinguals.

Rather than specifying spatial relations with a closed-class set of prepositions, American Sign Language (ASL) encodes spatial relations using space itself via classifier constructions. In these constructions, handshape morphemes specify object type, and the position of the hands in signing space schematically represents the spatial relation between objects. A [15O]water PET study was conducted to investigate the neural regions engaged during the production of English prepositions and ASL locative classifier constructions in hearing subjects with deaf parents (ASL-English bilinguals). Ten subjects viewed line drawings depicting a spatial relation between two objects and were asked to produce either an ASL locative classifier construction or an English preposition that described the spatial relation. The comparison task was to name the figure object (colored red) in either ASL or in English. Describing spatial relations in either ASL or English engaged parietal cortex bilaterally. However, an interaction analysis revealed that right superior parietal cortex was engaged to a greater extent for ASL than for English. We propose that right parietal cortex is involved in the visual-motoric transformation required for ASL. The production of both English prepositions and ASL nouns engaged Broca's area to a greater extent than ASL classifier constructions. We suggest that Broca's area is not engaged because these constructions do not involve retrieval of the name of an object or the name of a spatial relation. Finally, under the same task conditions, only left parietal activation was observed for monolingual English speakers producing spatial prepositions (H. Damasio et al., 2001, NeuroImage, 13). We conclude that the right hemisphere activation observed for ASL-English bilinguals was due to their life-long experience with spatial language in ASL.

Adult↗
PubMed2001

Impact of early deafness and early exposure to sign language on the cerebral organization for motion processing.

This functional magnetic resonance imaging study investigated the impact of early auditory deprivation and/or use of a visuospatial language [American sign language (ASL)] on the organization of neural systems important in visual motion processing by comparing hearing controls with deaf and hearing native signers. Participants monitored moving flowfields under different conditions of spatial and featural attention. Recruitment of the motion-selective area MT-MST in hearing controls was observed to be greater when attention was directed centrally and when the task was to detect motion features, confirming previous reports that the motion network is selectively modulated by different aspects of attention. More importantly, we observed marked differences in the recruitment of motion-related areas as a function of early experience. First, the lateralization of MT-MST was found to shift toward the left hemisphere in early signers, suggesting that early exposure to ASL leads to a greater reliance on the left MT-MST. Second, whereas the two hearing populations displayed more MT-MST activation under central than peripheral attention, the opposite pattern was observed in deaf signers, indicating enhanced recruitment of MT-MST during peripheral attention after early deafness. Third, deaf signers, but neither of the hearing populations, displayed increased activation of the posterior parietal cortex, supporting the view that parietal functions are modified after early auditory deprivation. Finally, only in deaf signers did attention to motion result in enhanced recruitment of the posterior superior temporal sulcus, establishing for the first time in humans that this polymodal area is modified after early sensory deprivation. Together these results highlight the functional and regional specificity of neuroplasticity in humans.

Adolescent↗
PubMed1991

Recessive hereditary deafness, assortative mating, and persistence of a sign language.

We model the cultural transmission of sign language when there is one-locus genetic variation for deafness and hearing. Our premises are that the deaf are more motivated to learn sign language than the hearing, and that a vertically transmitted sign language, unlike recessive hereditary deafness, cannot "jump a generation." Conditions are obtained for persistence (i.e. protection from loss) of signers. These conditions are more easily satisfied the greater the fraction of the hearing who also learn sign language and as the frequency of the recessive gene for deafness increases. Persistence is also facilitated by assortative mating for deafness, but not by assortment for signing. With vertical transmission only, it is necessary that one signer parent be able to transmit sign language with greater than one-half the efficiency of two. Under the assumption that the hearing do not learn sign language, the following additional results are obtained. Persistence is more likely with dominant as opposed to recessive inheritance. When recessive hereditary and acquired deafness co-occur, increasing the frequency of the latter has opposite effects depending on the degree of assortment. Opportunities for the deaf to learn sign language outside the family seem not to affect the conditions for persistence.

Deafness↗
PubMed1983

Processes controlling human movement: neuromotor constraints on American Sign Language.

The study of sign languages provides a promising vehicle for investigating language production because the movements of the articulators in sign are directly observable. Movement of the hands and arms is an essential element not only in the lexical structure of American Sign Language (ASL), but most strikingly, in the grammatical structure of ASL: It is in patterned changes of the movement of signs that many grammatical attributes are represented. The "phonological" (formational) structure of movement in ASL surely reflects in part constraints on the channel through which it is conveyed. We evaluate the relation between one neuromotor constraint on movement-regulation of final position rather than of movement amplitude-and the phonological structure of movement in ASL. We combine three-dimensional measurements of ASL movements with linguistic analyses of the distinctiveness and predictability of the final position (location) versus the amplitude (length). We show that final position, not movement amplitude, is distinctive in the language and that a phonological rule in ASL predicts variation in movement amplitude-a development which may reflect a neuromuscular constraint on the articulatory mechanism through which the language is conveyed.

Journal Article↗