Communication and reasoning skills of deaf and hearing signers

Six tests of intellectual performance were administered to 25 deaf and 21 hearing adult signers. The two groups were not significantly different on tests of Lip Reading and Reception of Signed English but the hearing subjects were superior on tests of non-verbal reasoning and perceptual speed. The hearing were greatly superior on a test of verbal reasoning.     

The effects of spatial attention on motion processing in deaf signers,hearing signers,and hearing nonsigners

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.     

Visual field asymmetries for motion processing in deaf and hearing signers

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.     

Temporal processing in deaf signers

The auditory and visual modalities differ in their capacities for temporal analysis, and speech relies on more rapid temporal contrasts than does sign language. We examined whether congenitally deaf signers show enhanced or diminished capacities for processing rapidly varying visual signals in light of the differences in sensory and language experience of deaf and hearing individuals. Four experiments compared rapid temporal analysis in deaf signers and hearing subjects at three different levels: sensation, perception, and memory. Experiment 1 measured critical flicker frequency thresholds and Experiment 2, two-point thresholds to a flashing light. Experiments 3-4 investigated perception and memory for the temporal order of rapidly varying nonlinguistic visual forms. In contrast to certain previous studies, specifically those investigating the effects of short-term sensory deprivation, no significant differences between deaf and hearing subjects were found at any level. Deaf signers do not show diminished capacities for rapid temporal analysis, in comparison to hearing individuals. The data also suggest that the deficits in rapid temporal analysis reported previously for children with developmental language delay cannot be attributed to lack of experience with speech processing and production.     

Visual-spatial processing in deaf brain-damaged signers

Sign language displays all the complex linguistic structure found in spoken languages, but conveys its syntax in large part by manipulating spatial relations. This study investigated whether deaf signers who rely on a visual-spatial language nonetheless show a principled cortical separation for language and nonlanguage visual-spatial functioning. Four unilaterally brain-damaged deaf signers, fluent in American Sign Language (ASL) before their strokes, served as subjects. Three had damage to the left hemisphere and one had damage to the right hemisphere. They were administered selected tests of nonlanguage visual-spatial processing. The pattern of performance of the four patients across this series of tests suggests that deaf signers show hemispheric specialization for nonlanguage visual-spatial processing that is similar to hearing speaking individuals. The patients with damage to the left hemisphere, in general, appropriately processed visual-spatial relationships, whereas, in contrast, the patient with damage to the right hemisphere showed consistent and severe visual-spatial impairment. The language behavior of these patients was much the opposite, however. Indeed, the most striking separation between linguistic and nonlanguage visual-spatial functions occurred in the left-hemisphere patient who was most severely aphasic for sign language. Her signing was grossly impaired, yet her visual-spatial capacities across the series of tests were surprisingly normal. These data suggest that the two cerebral hemispheres of congenitally deaf signers can develop separate functional specialization for nonlanguage visual-spatial processing and for language processing, even though sign language is conveyed in large part via visual-spatial manipulation.     

Memory in deaf signers and embodied cognition of sign languages

Abstract:  In the first half of this paper, the experimental investigations on memory and cognition in deaf signers are reviewed in order to reveal how deaf signers rely on sign-based coding when they process linguistic information. It is suggested that deaf signers tactically employ a set of originally separate memory strategies relying on multiple components of working memory. In the second half of this paper, the author shows possible factors that could contribute to a sign language advantage. It is indicated that deaf signers' cognitive activities are deeply rooted in the signers' interaction with the environment. Some concrete examples of Japanese Sign Language signs and their use are provided to support this hypothesis.     

Discourse deficits following right hemisphere damage in deaf signers

Previous findings have demonstrated that hemispheric organization in deaf users of American Sign Language (ASL) parallels that of the hearing population, with the left hemisphere showing dominance for grammatical linguistic functions and the right hemisphere showing specialization for non-linguistic spatial functions. The present study addresses two further questions: first, do extra-grammatical discourse functions in deaf signers show the same right-hemisphere dominance observed for discourse functions in hearing subjects; and second, do discourse functions in ASL that employ spatial relations depend upon more general intact spatial cognitive abilities? We report findings from two right-hemisphere damaged deaf signers, both of whom show disruption of discourse functions in absence of any disruption of grammatical functions. The exact nature of the disruption differs for the two subjects, however. Subject AR shows difficulty in maintaining topical coherence, while SJ shows difficulty in employing spatial discourse devices. Further, the two subjects are equally impaired on non-linguistic spatial tasks, indicating that spared spatial discourse functions can occur even when more general spatial cognition is disrupted. We conclude that, as in the hearing population, discourse functions involve the right hemisphere; that distinct discourse functions can be dissociated from one another in ASL; and that brain organization for linguistic spatial devices is driven by its functional role in language processing, rather than by its surface, spatial characteristics.     

Brain activations associated with sign production using word and picture inputs in deaf signers

Effective literacy education in deaf students calls for psycholinguistic research revealing the cognitive and neural mechanisms underlying their written language processing. When learning a written language, deaf students are often instructed to sign out printed text. The present fMRI study was intended to reveal the neural substrates associated with word signing by comparing it with picture signing. Native deaf signers were asked to overtly sign in Chinese Sign Language (CSL) common objects indicated with written words or presented as pictures. Except in left inferior frontal gyrus and inferior parietal lobule where word signing elicited greater activation than picture signing, the two tasks engaged a highly overlapping set of brain regions previously implicated in sign production. The results suggest that word signing in the deaf signers relies on meaning activation from printed visual forms, followed by similar production processes from meaning to signs as in picture signing. The present study also documents the basic brain activation pattern for sign production in CSL and supports the notion of a universal core neural network for sign production across different sign languages.     

Belief attribution in deaf and hearing infants

Based on anticipatory looking and reactions to violations of expected events, infants have been credited with 'theory of mind' (ToM) knowledge that a person's search behaviour for an object will be guided by true or false beliefs about the object's location. However, little is known about the preconditions for looking patterns consistent with belief attribution in infants. In this study, we compared the performance of 17- to 26-month-olds on anticipatory looking in ToM tasks. The infants were either hearing or were deaf from hearing families and thus delayed in communicative experience gained from access to language and conversational input. Hearing infants significantly outperformed their deaf counterparts in anticipating the search actions of a cartoon character that held a false belief about a target-object location. By contrast, the performance of the two groups in a true belief condition did not differ significantly. These findings suggest for the first time that access to language and conversational input contributes to early ToM reasoning.     

Semantic organization in deaf and hearing subjects

Hierarchical cluster analysis of data from the sorting of noun words was used to compare semantic structures in 63 profoundly deaf and 63 hearing adolescents. In the first study, performance differed only for a set of words referring to sounds, where deaf persons have no experience, and not for a set of common noun words and pictures. In the second study, differences between matched sets of high- and low-imagery words were comparable for 63 deaf and 63 hearing subjects. It is concluded that deaf subjects manifested abstract hierarchical relations and were not dependent on visual mediators or hindered by the absence of acoustic mediators.This investigation was supported in part by National Institutes of Health Research Grant NS-09590-03 from the National Institute of Neurological Diseases and Stroke and in part by a Faculty Research Grant from Bowling Green State University.Portions of Study 1 were previously reported at the Eighty-first Annual Convention of the American Psychological Association, Montreal, 1973.     

Sign recall by hearing signers: Evidences of dual coding

Deaf participants' sign recall is affected by sign similarity, sign length, irrelevant signing and manual articulatory suppression, suggesting the existence of a phonological loop for signs. In two experiments we explore whether hearing signers (who have learned Spanish Sign Language as second language) use a phonological loop for signs, whether they use their phonological loop for words or whether they use both when recalling sign lists. Articulatory suppression (manual and vocal) and list similarity (word similarity and sign similarity) were manipulated in two experiments. Results clearly suggest that our participants recode orally the signs and use those representations to recall sign lists, but visuospatial information is also used in this task.     

Short-term memory coding by deaf signers: the primary language coding hypothesis reconsidered

Shand (Cognitive Psychology, 1982, 14, 1-12) hypothesized that strong reliance on a phonetic code by hearing individuals in short-term memory situations reflects their primary language experience. As support for this proposal, Shand reported an experiment in which deaf signers' recall of lists of printed English words was poorer when the American Sign Language translations of those words were structurally similar than when they were structurally unrelated. He interpreted this result as evidence that the deaf subjects were recoding the printed words into sign, reflecting their primary language experience. This primary language interpretation is challenged in the present article first by an experiment in which a group of hearing subjects showed a similar recall pattern on Shand's lists of words, and second by a review of the literature on short-term memory studies with deaf subjects. The literature survey reveals that whether or not deaf signers recode into sign depends on a variety of task and subject factors, and that, contrary to the primary language hypothesis, deaf signers may recode into a phonetic code in short-term recall.     

Intralist interference and imagery in deaf and hearing children

Children from populations lacking verbal proficiency were given an interference list of paired associates (high within-list stimulus similarity) or 1 of 2 noninterference lists (low stimulus similarity), under a standard control condition (pictorial items side by side) or an imagery condition (items depicted as interacting). In Experiment I, with deaf children 6–10 years old, the imagery condition facilitated performance on the interference list, mainly by reducing generalization errors. There was significant interference only in the control condition. Unexpectedly, imagery failed to improve performance on the noninterference lists. In Experiment II, with hearing children 4–5 years old, there was significant interference in both the imagery and the control condition. Imagery significantly facilitated performance in all lists, but did not reduce interference, apparently because it did not reduce generalization errors. Thus, imagery (a) facilitates performance by increasing the memorability of stimulus-response associations, and (b) reduces interference by reducing confusion among similar stimuli.     

Neural substrates for verbal working memory in deaf signers: fMRI study and lesion case report

The nature of the representations maintained in verbal working memory is a topic of debate. Some authors argue for a modality-dependent code, tied to particular sensory or motor systems. Others argue for a modality-neutral code. Sign language affords a unique perspective because it factors out the effects of modality. In an fMRI experiment, deaf participants viewed and covertly rehearsed strings of non-sense signs; analyses focused on regions responsive in both sensory and rehearsal phases. Compared with previous findings in hearing subjects, deaf subjects showed a significantly increased involvement of parietal regions. A lesion case study indicates that this network is left-dominant. The findings support the hypothesis that linguistic working memory is supported by modality-specific neural systems, but some modality-neutral systems may also be involved.     

Recall of order information by deaf signers: Phonetic coding in temporal order recall

To examine the claim that phonetic coding plays a special role in temporal order recall, deaf and hearing college students were tested on their recall of temporal and spatial order information at two delay intervals. The deaf subjects were all native signers of American Sign Language. The results indicated that both the deaf and hearing subjects used phonetic coding in short-term temporal recall, and visual coding in spatial recall. There was no evidence of manual or visual coding among either the hearing or the deaf subjects in the temporal order recall task. The use of phonetic coding for temporal recall is consistent with the hypothesis that recall of temporal order information is facilitated by a phonetic code.     

Parafoveal attention in congenitally deaf and hearing young adults

This reaction-time study compared the performance of 20 congenitally and profoundly deaf, and 20 hearing college students on a parafoveal stimulus detection task in which centrally presented prior cues varied in their informativeness about stimulus location. In one condition, subjects detected a parafoveally presented circle with no other information being present in the visual field. In another condition, spatially complex and task-irrelevant foveal information was present which the subjects were instructed to ignore. The results showed that although both deaf and hearing people utilized cues to direct attention to specific locations and had difficulty in ignoring foveal information, deaf people were more proficient in redirecting attention from one spatial location to another in the presence of irrelevant foveal information. These results suggest that differences exist in the development of attentional mechanisms in deaf and hearing people. Both groups showed an overall right visual-field advantage in stimulus detection which was attenuated when the irrelevant foveal information was present. These results suggest a left-hemisphere superiority for detection of parafoveally presented stimuli independent of cue informativeness for both groups.