Deaf Native Signers Research Articles

Visual memory for shapes in deaf signers and nonsigners and in hearing signers and nonsigners: Atypical lateralization and enhancement.

Deaf and hearing individuals who either used sign language (signers) or not (nonsigners) were tested on visual memory for objects and shapes that were difficult to describe verbally with a same/different matching paradigm. The use of 4 groups was designed to permit a separation of effects related to sign language use (signers vs. nonsigners) and effects related to auditory deprivation (deaf vs. hearing). Forty deaf native signers and nonsigners and 51 hearing signers and nonsigners participated in the study. Signing individuals (both deaf and hearing) were more accurate than nonsigning individuals (deaf and hearing) at memorizing shapes. For the shape memory task but not the object task, deaf signers and nonsigners displayed right hemisphere (RH) advantage over the left hemisphere (LH). Conversely, both hearing groups displayed a memory advantage for shapes in the LH over the RH. Results indicate that enhanced memory performance for shapes in signers (deaf and hearing) stems from the visual skills acquired through sign language use and that deafness, irrespective of language background, leads to the use of a visually based strategy for memory of difficult-to-describe items.

Visual Constructive and Visual-Motor Skills in Deaf Native Signers

Visual constructive and visual-motor skills in the deaf population were investigated by comparing performance of deaf native signers (n=20) to that of hearing nonsigners (n=20) on the Beery-Buktenica Developmental Test of Visual-Motor Integration, Rey-Osterrieth Complex Figure Test, Wechsler Memory Scale Visual Reproduction subtest, and Stanford-Binet Intelligence Scale Paper Folding and Cutting subtest. Deaf signers were found to perform similarly to hearing controls, suggesting that these tests are valid assessment instruments to use with deaf individuals.

Comparing Action Gestures and Classifier Verbs of Motion: Evidence From Australian Sign Language, Taiwan Sign Language, and Nonsigners' Gestures Without Speech

Recent research into signed languages indicates that signs may share some properties with gesture, especially in the use of space in classifier constructions. A prediction of this proposal is that there will be similarities in the representation of motion events by sign-naive gesturers and by native signers of unrelated signed languages. This prediction is tested for deaf native signers of Australian Sign Language (Auslan), deaf signers of Taiwan Sign Language (TSL), and hearing nonsigners using the Verbs of Motion Production task from the Test Battery for American Sign Language (ASL) Morphology and Syntax. Results indicate that differences between the responses of nonsigners, Auslan signers, and TSL signers and the expected ASL responses are greatest with handshape units; movement and location units appear to be very similar. Although not definitive, these data are consistent with the claim that classifier constructions are blends of linguistic and gestural elements.

Dissociating linguistic and nonlinguistic gestural communication in the brain

Gestures of the face, arms, and hands are components of signed languages used by Deaf people. Signaling codes, such as the racecourse betting code known as Tic Tac, are also made up of such gestures. Tic Tac lacks the phonological structure of British Sign Language (BSL) but is similar in terms of its visual and articulatory components. Using fMRI, we compared the neural correlates of viewing a gestural language (BSL) and a manual-brachial code (Tic Tac) relative to a low-level baseline task. We compared three groups: Deaf native signers, hearing native signers, and hearing nonsigners. None of the participants had any knowledge of Tic Tac. All three groups activated an extensive frontal-posterior network in response to both types of stimuli. Superior temporal cortex, including the planum temporale, was activated bilaterally in response to both types of gesture in all groups, irrespective of hearing status. The engagement of these traditionally auditory processing regions was greater in Deaf than hearing participants. These data suggest that the planum temporale may be responsive to visual movement in both deaf and hearing people, yet when hearing is absent early in development, the visual processing role of this region is enhanced. Greater activation for BSL than Tic Tac was observed in signers, but not in nonsigners, in the left posterior superior temporal sulcus and gyrus, extending into the supramarginal gyrus. This suggests that the left posterior perisylvian cortex is of fundamental importance to language processing, regardless of the modality in which it is conveyed.

Motion velocity thresholds in deaf signers: changes in lateralization but not in overall sensitivity

In a series of three experiments, we tested whether deaf native signers process motion velocity information differently from hearing nonsigners. In Experiment 1, participants watched radially moving dots and were asked to detect the quadrant in which the velocity of the dots had changed. Similar 79% thresholds were observed in the two populations. In Experiments 2 and 3, peripheral and central thresholds were assessed separately as previous studies suggest early deafness leads mainly to changes in the processing of visual peripheral information. Neither condition produced an overall population difference. These negative results were not due to a lack of sensitivity in our experiments. Indeed, as has been previously reported, deaf native signers exhibited better thresholds in the right than in the left visual field, whereas the opposite pattern was observed in the hearing. This effect appears triggered by experience with American Sign Language (ASL) rather than deafness per se. Overall, this study confirms that early deafness does not enhance motion processing, and suggests that most of the changes previously described in the literature are instead attributable to changes in attention, and possibly special alterations of attention-to-motion processes.

Neural Systems Underlying Spatial Language in American Sign Language

A [15O]water PET experiment was conducted to investigate the neural regions engaged in processing constructions unique to signed languages: classifier predicates in which the position of the hands in signing space schematically represents spatial relations among objects. Ten deaf native signers viewed line drawings depicting a spatial relation between two objects (e.g., a cup on a table) and were asked either to produce a classifier construction or an American Sign Language (ASL) preposition that described the spatial relation or to name the figure object (colored red). Compared to naming objects, describing spatial relationships with classifier constructions engaged the supramarginal gyrus (SMG) within both hemispheres. Compared to naming objects, naming spatial relations with ASL prepositions engaged only the right SMG. Previous research indicates that retrieval of English prepositions engages both right and left SMG, but more inferiorly than for ASL classifier constructions. Compared to ASL prepositions, naming spatial relations with classifier constructions engaged left inferior temporal (IT) cortex, a region activated when naming concrete objects in either ASL or English. Left IT may be engaged because the handshapes in classifier constructions encode information about object type (e.g., flat surface). Overall, the results suggest more right hemisphere involvement when expressing spatial relations in ASL, perhaps because signing space is used to encode the spatial relationship between objects.

Neural Systems Underlying Spatial Language in American Sign Language

A [ 15O]water PET experiment was conducted to investigate the neural regions engaged in processing constructions unique to signed languages: classifier predicates in which the position of the hands in signing space schematically represents spatial relations among objects. Ten deaf native signers viewed line drawings depicting a spatial relation between two objects (e.g., a cup on a table) and were asked either to produce a classifier construction or an American Sign Language (ASL) preposition that described the spatial relation or to name the figure object (colored red). Compared to naming objects, describing spatial relationships with classifier constructions engaged the supramarginal gyrus (SMG) within both hemispheres. Compared to naming objects, naming spatial relations with ASL prepositions engaged only the right SMG. Previous research indicates that retrieval of English prepositions engages both right and left SMG, but more inferiorly than for ASL classifier constructions. Compared to ASL prepositions, naming spatial relations with classifier constructions engaged left inferior temporal (IT) cortex, a region activated when naming concrete objects in either ASL or English. Left IT may be engaged because the handshapes in classifier constructions encode information about object type (e.g., flat surface). Overall, the results suggest more right hemisphere involvement when expressing spatial relations in ASL, perhaps because signing space is used to encode the spatial relationship between objects.

Signposts to development: theory of mind in deaf children.

Possession of a "theory of mind" (ToM)--as demonstrated by an understanding of the false beliefs of others--is fundamental in children's cognitive development. A key question for debate concerns the effect of language input on ToM. In this respect, comparisons of deaf native-signing children who are raised by deaf signing parents with deaf late-signing children who are raised by hearing parents provide a critical test. This article reports on two studies (N = 100 and N = 39) using "thought picture" measures of ToM that minimize verbal task-performance requirements. These studies demonstrated that even when factors such as syntax ability, mental age in spatial ability, and executive functioning were considered, deaf late signers still showed deficits in ToM understanding relative to deaf native signers or hearing controls. Even though the native signers were significantly younger than a sample of late signers matched for spatial mental age and scores on a test of receptive sign language ability, native signers outperformed late signers on pictorial ToM tasks. The results are discussed in terms of access to conversation and extralinguistic influences on development such as the presence of sibling relationships, and suggest that the expression of a ToM is the end result of social understanding mediated by early conversational experience.

Issues in development of the test battery for Australian sign language morphology and syntax.

In this article, we outline the initial stages in development of an assessment instrument for Australian Sign Language and explore issues involved in the development of such a test. We first briefly describe the instruments currently available for assessing grammatical skills in Australian Sign Language and discuss the need for a more objective measure. We then describe our adaptation of an existing American Sign Language test, the Test Battery for American Sign Language Morphology and Syntax. Finally, this article presents some of the data collected from a group of deaf native signers. These data are used to demonstrate the range of variability in key grammatical features of Australian Sign Language and to raise methodological issues associated with signed language test design.

Written Language Abilities in Deaf Italians

Written texts produced by 10 Italian deaf native signers in four different writing tasks were analyzed. Data analysis focused on linguistic and orthographic nonstandard forms. The written production of deaf subjects with deaf parents (DD) was compared to the written production in two control groups: a group of 10 hearing subjects with deaf parents (HD) and a group of 10 subjects who have had no contact with deaf people or sign language (HH). The results duplicate findings from previous studies. Deaf subjects display a pattern of selective difficulty with Italian grammatical morphology, especially with free-standing function words. The four different writing tasks used in the present study yield results indicating that text type does influence our assessment of deaf writing abilities. A comparison of the texts written by deaf native signers with those of two hearing groups confirms the view that difficulties in the acquisition of written Italian are best explained by deafness itself, not by the influence of a previously acquired Sign Language, and that the specific difficulties with grammatical morphology displayed by our deaf subjects cannot be attributed solely to their limited experience with written Italian.

Neural Systems Mediating American Sign Language: Effects of Sensory Experience and Age of Acquisition

ERPs were recorded from deaf and hearing native signers and from hearing subjects who acquired ASL late or not at all as they viewed ASL signs that formed sentences. The results were compared across these groups and with those from hearing subjects reading English sentences. The results suggest that there are constraints on the organization of the neural systems that mediate formal languages and that these are independent of the modality through which language is acquired. These include different specializations of anterior and posterior cortical regions in aspects of grammatical and semantic processing and a bias for the left hemisphere to mediate aspects of mnemonic functions in language. Additionally, the results suggest that the nature and timing of sensory and language experience significantly impact the development of the language systems of the brain. Effects of the early acquisition of ASL include an increased role for the right hemisphere and for parietal cortex and this occurs in both hearing and deaf native signers. An increased role of posterior temporal and occipital areas occurs in deaf native signers only and thus may be attributable to auditory deprivation.

The basis of hemispheric asymmetries for language and spatial cognition: Clues from focal brain damage in two deaf native signers

Abstract The existence of hemispheric asymmetries for language processing and visuospatial processing is well established. In this report we investigate the basis of these asymmetries through the window of American Sign Language (ASL). ASL uses spatial contrasts to encode grammatical information at all levels of representation, including phonology, morphology, and syntax. In addition, however, ASL uses space in an iconic fashion to represent spatial information directly, as, for example, in describing the layout of objects in a room. We tested the performance of two deaf, native signers—one with left hemisphere damage (LHD) and one with right hemisphere damage (RHD)—on tasks involving the use of space, within ASL, to represent linguistic versus spatial information. We found a double dissociation: the LHD signer was impaired on tasks involving the use of space for encoding grammatical information, but performed well on tasks involving the use of space to encode spatial information iconically; the RHD signe...

Perceptual Evidence Against Internal Structure in American Sign Language Syllables

Syllables in spoken languages have been argued to have an internal structure which may cluster the consonants and vowels into subgroups. The most commonly used subgroups are the Onset (initial consonants) and Rhyme (vowel and remaining consonants), with the further possibility of dividing the Rhyme into Nucleus (the vowel and any on- or off-glides) and the Coda (the final consonants). Although linguistic debate continues about the exact formulation of such syllable models, the evidence is clear that listeners identify rhythmic beats at a particular point inside the syllable, namely at the release of the initial consonants into the following linguistically stressed vowels (referred to as the syllable peak, assumed to be part of the Nucleus). To determine whether such loci would be identified for syllables in American Sign Language, deaf native signers, hearing native signers, and hearing subjects unfamiliar with sign language were asked to tap to videotaped signed stimuli. Analysis of the tap locations in signed syllables revealed a relatively flat distribution across the syllable for all three groups and for individual subjects. The absence of syllable peak perception is discussed in relation to the motoric characteristics of sign production.

Perception of movement in American Sign Language: effects of linguistic structure and linguistic experience.

In order to reveal the psychological representation of movement from American Sign Language (ASL), deaf native signers and hearing subjects unfamiliar with sign were asked to make triadic comparisons of movements that had been isolated from lexical and from grammatically inflected signs. An analysis of the similarity judgments revealed a small set of physically specifiable dimensions that accounted for most of the variance. The dimensions underlying the perception of lexical movement were in general different from those underlying inflectional movement, for both groups of subjects. Most strikingly, deaf and hearing subjects significantly differed in their patterns of dimensional salience for movements, both at the lexical and at the inflectional levels. Linguistically relevant dimensions were of increased salience to native signers. The difference in perception of linguistic movement by native signers and by naive observers demonstrates that modification of natural perceptual categories after language acquisition is not bound to a particular transmission modality, but rather can be a more general consequence of acquiring a formal linguistic system.

Visual and "Phonetic" Coding of Movement: Evidence from American Sign Language

Hearing subjects unfamiliar with American Sign Language and deaf native signers made triadic comparisons of movements of the hands and arms isolated from American Sign Language. Clustering and scaling of subjects' judgments revealed different psychological representations of movement form for deaf and hearing observerd. Linguistically relevant dimensions acquired modified salience for users ofa visual-gestural language. The data indicate that the modification of natural perceptual categories after language acquisition is not bound to a particular transmission modality, but rather can be a more general consequence of acquiring a formal linguistic system.