Intelligence and handedness: Meta-analyses of studies on intellectually disabled,typically developing,and gifted individuals

Understanding the relationship between cerebral laterality and intelligence is important in elucidating the neurological underpinnings of individual differences in cognitive abilities. A widely used, behavioral indicator for cerebral laterality, mainly of language, is handedness. A number of studies have compared cognitive abilities between groups of left- and right-handers, while others have investigated the handedness prevalence between groups of different cognitive abilities. The present study comprises five meta-analyses of studies that have assessed the handedness prevalence in (a) individuals with intellectual disability (ID) of unknown/idiopathic nature compared to typically developing (TD) individuals, and (b) individuals with intellectual giftedness (IG) compared to TD individuals. Nineteen data sets totaling 16,076 participants (5795 ID, 8312 TD, and 1969 IG) were included in the analyses. Elevated levels of atypical handedness were found to be robust only for the ID to TD comparison. Findings constrain the range of acceptable theories on the handedness distribution for different intelligence levels.     

Psychosoziale Merkmale bei Gehörlosen

In this publication, data from a special outpatient clinic for deaf patients in a general hospital are presented. All members of the treatment team have competency in sign language. From the patients who consecutively attended the outpatient clinic, 352 were investigated for medical and psychosocial problems. In social contacts, there is a strong orientation towards other deaf people, and communication is mainly based on sign language. Of the deaf patients, 85% of their partners are also deaf, whereas only 10.1% of children of the deaf group are also deaf. The prevalence of selected psychiatric disorders (ICD 10 F1, F2, F3, F4, F6) in deaf people was found to be similar to that in hearing populations, with the exception of somatoform disorders, which seem to be more frequent in the deaf. Deaf people also more often present with somatic and other complaints such as nervousness, anxiety, and stress. With specific outpatient clinics for the deaf in which members of the therapeutic team are competent in sign language, access to health services is equally possible for deaf people.     

The perceptual characteristics of voice-hallucinations in deaf people: insights into the nature of subvocal thought and sensory feedback loops

The study of voice-hallucinations in deaf individuals, who exploit the visuomotor rather than auditory modality for communication, provides rare insight into the relationship between sensory experience and how "voices" are perceived. Relatively little is known about the perceptual characteristics of voice-hallucinations in congenitally deaf people who use lip-reading or sign language as their preferred means of communication. The existing literature on hallucinations in deaf people is reviewed, alongside consideration of how such phenomena may fit into explanatory subvocal articulation hypotheses proposed for auditory verbal hallucinations in hearing people. It is suggested that a failure in subvocal articulation processes may account for voice-hallucinations in both hearing and deaf people but that the distinct way in which hallucinations are experienced may be due to differences in a sensory feedback component, which is influenced by both auditory deprivation and language modality. This article highlights how the study of deaf people may inform wider understanding of auditory verbal hallucinations and subvocal processes generally.     

Signed words in the congenitally deaf evoke typical late lexicosemantic responses with no early visual responses in left superior temporal cortex

Congenitally deaf individuals receive little or no auditory input, and when raised by deaf parents, they acquire sign as their native and primary language. We asked two questions regarding how the deaf brain in humans adapts to sensory deprivation: (1) is meaning extracted and integrated from signs using the same classical left hemisphere frontotemporal network used for speech in hearing individuals, and (2) in deafness, is superior temporal cortex encompassing primary and secondary auditory regions reorganized to receive and process visual sensory information at short latencies? Using MEG constrained by individual cortical anatomy obtained with MRI, we examined an early time window associated with sensory processing and a late time window associated with lexicosemantic integration. We found that sign in deaf individuals and speech in hearing individuals activate a highly similar left frontotemporal network (including superior temporal regions surrounding auditory cortex) during lexicosemantic processing, but only speech in hearing individuals activates auditory regions during sensory processing. Thus, neural systems dedicated to processing high-level linguistic information are used for processing language regardless of modality or hearing status, and we do not find evidence for rewiring of afferent connections from visual systems to auditory cortex.     

Hand dominance for signing: clues to brain lateralization of language

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.     

Cerebellar activation patterns in deaf participants for perception of sign language and written text

To address the influence of language presentation on cerebellar activation, hearing volunteers were compared with deaf individuals using functional magnetic resonance imaging during observation of German sign language and text reading. In deaf participants, German sign language revealed activation of the auditory and language-related areas including the medial temporal gyrus (BA 21) and Crus I. In normal hearing participants not understanding German sign language, Crus I was less activated during observation of German sign language but strongly activated during text reading and accompanied by activation of the medial temporal gyrus. Our results indicate that cerebellar activation in Crus I corresponds to language perception as correlated with cortical activation in language-related areas and is not dependent on the mode of language presentation.     

Changes in the spatial distribution of visual attention after early deafness

There is much anecdotal suggestion of improved visual skills in congenitally deaf individuals. However, this claim has only been met by mixed results from careful investigations of visual skills in deaf individuals. Psychophysical assessments of visual functions have failed, for the most part, to validate the view of enhanced visual skills after deafness. Only a few studies have shown an advantage for deaf individuals in visual tasks. Interestingly, all of these studies share the requirement that participants process visual information in their peripheral visual field under demanding conditions of attention. This work has led us to propose that congenital auditory deprivation alters the gradient of visual attention from central to peripheral field by enhancing peripheral processing. This hypothesis was tested by adapting a search task from Lavie and colleagues in which the interference from distracting information on the search task provides a measure of attentional resources. These authors have established that during an easy central search for a target, any surplus attention remaining will involuntarily process a peripheral distractor that the subject has been instructed to ignore. Attentional resources can be measured by adjusting the difficulty of the search task to the point at which no surplus resources are available for the distractor. Through modification of this paradigm, central and peripheral attentional resources were compared in deaf and hearing individuals. Deaf individuals possessed greater attentional resources in the periphery but less in the center when compared to hearing individuals. Furthermore, based on results from native hearing signers, it was shown that sign language alone could not be responsible for these changes. We conclude that auditory deprivation from birth leads to compensatory changes within the visual system that enhance attentional processing of the peripheral visual field.     

Cross-modal plasticity in deaf subjects dependent on the extent of hearing loss

Cross-modal plasticity in deaf subjects is still discussed controversial. We tried to figure out whether the plasticity is dependent on the extent of hearing loss. Three groups of volunteers, comprising twelve individuals each, were investigated. They were characterized by three distinctive features, one had normal hearing, the other one lost hearing and the third had only minimal residual hearing ability. All participants, except those of group one, were capable of using German Sign Language (GSL). The groups were studied with functional MRI in a standard block design during individuals' watching sign language videos alternating with black frame. During sign language conditions, deaf subjects revealed a significant activation of the auditory cortex in both hemispheres comprising Brodmann areas (BA) 42 and 22 corresponding to the secondary associative auditory areas. Additionally, activation of the angular and supramarginal gyrus was seen. Activation of the primary auditory cortex was revealed in deaf subjects with total hearing loss during sign language tasks but not in subjects with residual hearing ability. In conclusion our results indicate a cortical reorganization of the auditory cortex comprising primary auditory fields only present in subjects with total hearing loss.     

Facial affect recognition in pre-lingually deaf people with schizophrenia

The present study examined facial affect recognition in pre-lingually deaf individuals with schizophrenia. Affective facial-labeling task and the control task of face feature processing (the Benton facial recognition test) were performed by deaf subjects with schizophrenia using French sign language (FSL), hearing subjects with schizophrenia, and hearing healthy controls. Deaf subjects with schizophrenia performed more poorly than hearing clinical controls with schizophrenia or healthy controls on the affective facial-labeling task. No differences were found on the control task between deaf subjects with schizophrenia and hearing clinical or healthy controls. The results showed that facial affect recognition and face feature processing were differently impaired in pre-lingually deaf individuals with schizophrenia, suggesting that neurocognitive backgrounds of impaired affective facial processing may be distinct from those of general impairment in face processing.     

Issues in the modification of american sign language for instructional purposes

The use of manual communication and sign languages for language education of autistic, deaf retarded, and mentally retarded individuals is receiving increasing attention by educators. Modifications of sign systems for this purpose emphasize simplicity, redundancy, and English word order. Effective utilization of manual communication for these populations requires a better understanding of the physical and linguistic bases of sign languages than now exists. Preliminary evidence from studies of oralonly, manualonly, and oralmanual modes of communication suggests that flexibility in utilizing all modes is the most effective teaching method. The present paper will consider the possible utilization of modifications of the American Sign Language for use in three general areas: (1) instruction of deaf students in the classroom, (2) communication between hearing parents and young deaf children, and (3) communication with individuals with handicaps other than deafness.     

Sign language aphasia following right hemisphere damage in a left-hander: a case of reversed cerebral dominance in a deaf signer?

Recent lesion studies have shown that left hemisphere lesions often give rise to frank sign language aphasias in deaf signers, whereas right hemisphere lesions do not, suggesting similar patterns of hemispheric asymmetry for signed and spoken language. We present here a case of a left-handed, deaf, life-long signer who became aphasic after a right-hemisphere lesion. The subject exhibits deficits in sign language comprehension and production typically associated with left hemisphere damaged signers. He also exhibits evidence of local versus global deficits similar to left-hemisphere lesioned hearing patients. This case represents reversed lateralization for sign language and also may represent reversed lateralization for visuo-spatial abilities in a deaf signer.     

Selective,Non-lateralized Impairment of Motor Imagery Following Right Parietal Damage

Recent lesion studies have shown that left hemisphere lesions often give rise to frank sign language aphasias in deaf signers, whereas right hemisphere lesions do not, suggesting similar patterns of hemispheric asymmetry for signed and spoken language. We present here a case of a left-handed, deaf, life-long signer who became aphasic after a right-hemisphere lesion. The subject exhibits deficits in sign language comprehension and production typically associated with left hemisphere damaged signers. He also exhibits evidence of local versus global deficits similar to left-hemisphere lesioned hearing patients. This case represents reversed lateralization for sign language and also may represent reversed lateralization for visuo-spatial abilities in a deaf signer.     

Diagnostic considerations in deaf patients

Mental health professionals who are unfamiliar with the psychosocial development of prelingually deaf individuals are likely to misdiagnose deaf patients. Concrete and sometimes fragmented deaf communication can be similar to the disordered language present in schizophrenic and organic mental disorders. Egocentric and rigid behaviors, products of deaf enculturation, can be mistaken for personality disorders. Linguistic and cultural differences limit the usefulness of standard assessment methods such as the mental status examination and psychological testing. An awareness of the complex problems associated with hearing impairment and the assistance of a professional trained in deafness are indispensable in the evaluation of deaf patients.     

Comparing the effects of auditory deprivation and sign language within the auditory and visual cortex

To investigate neural plasticity resulting from early auditory deprivation and use of American Sign Language, we measured responses to visual stimuli in deaf signers, hearing signers, and hearing nonsigners using functional magnetic resonance imaging. We examined "compensatory hypertrophy" (changes in the responsivity/size of visual cortical areas) and "cross-modal plasticity" (changes in auditory cortex responses to visual stimuli). We measured the volume of early visual areas (V1, V2, V3, V4, and MT+). We also measured the amplitude of responses within these areas, and within the auditory cortex, to a peripheral visual motion stimulus that was attended or ignored. We found no major differences between deaf and hearing subjects in the size or responsivity of early visual areas. In contrast, within the auditory cortex, motion stimuli evoked significant responses in deaf subjects, but not in hearing subjects, in a region of the right auditory cortex corresponding to Brodmann's areas 41, 42, and 22. This hemispheric selectivity may be due to a predisposition for the right auditory cortex to process motion; earlier studies report a right hemisphere bias for auditory motion in hearing subjects. Visual responses within the auditory cortex of deaf subjects were stronger for attended than ignored stimuli, suggesting top-down processes. Hearing signers did not show visual responses in the auditory cortex, indicating that cross-modal plasticity can be attributed to auditory deprivation rather than sign language experience. The largest effects of auditory deprivation occurred within the auditory cortex rather than the visual cortex, suggesting that the absence of normal input is necessary for large-scale cortical reorganization to occur.     

Do deaf people see better? Texture segmentation and visual search compensate in adult but not in juvenile subjects.

The research concerning the visual perception in deaf subjects has led to contradictory results: Deaf subjects have been reported to show enhanced visual perceptual skills compared to hearing subjects (Neville & Lawson, 1987). On the other hand, there are indications that acoustic deprivation may produce an inferiority in all sensory modalities (Myklebust, 1964). These contradictions may be due to methodological differences: The investigators selected different conditions (e.g. attentive/nonattentive) and various samples of deaf subjects (e.g., different age, language, and aetiology groups). In our study, we tested a large sample of deaf subjects with texture segmentation and visual search conditions, which allowed us to differentiate between visual processing with and without attentional load. All deaf subjects had profound hearing loss within the first year of life. Our results suggest that the visual processing capacity of deaf children and adolescents does not exceed that of age- and gender-matched hearing subjects. Rather, deaf school children show deficits in visual processing in conditions with and without attentional load. Age (6 to 20 years), language used (oral, sign, oral + sign), and aetiology for deafness (genetic, maternal rubella, perinatal, infection in the first year of life, unknown) did not consistently influence the results. The deficits in visual processing were partially compensated for in adult deaf subjects. The performances of deaf and hearing adults in trials that could be solved preattentively did not differ statistically significantly, but in attention-dependent trials the deaf subjects were more efficient than the hearing controls. We conclude that visual compensation for deafness is limited to attention-dependent tasks and does not develop until adulthood.     

Comorbidity of schizophrenia and prelingual deafness: its impact on social network structures

Background: Prelingually deaf persons usually gain only a rudimentary command of speech and prefer sign language to communicate within the deaf community without the handicap they experience in the hearing world. Maintaining social contact within this rather scattered community, however, requires higher degrees of social initiative and mobility. The aim of the present paper was to study the quantity and quality of social integration among a group of prelingually deaf schizophrenic patients (n = 49) and two control groups comprising prelingually deaf psychiatric but non-psychotic patients (n = 38) and hearing schizophrenic patients (n = 30), with account being taken of the special socialisation conditions of deaf persons and of their cultural standards and values. Method: Data were collected with the help of semi-structured interviews; with the deaf patients these were conducted in German sign language. Using rating procedures we assessed seven social support components, selected items from a history schedule for schizophrenia, and the probands' visual and verbal language skills. Results: The social networks of the two deaf groups were found to have larger gaps than those of the hearing schizophrenic patients, with significant differences being registered most clearly in the comparison between deaf schizophrenic and hearing schizophrenic patients. Comparison of the verbal and visual language skills of the two deaf groups revealed a substantial deficit among the deaf schizophrenics. Visual language skills were found to correlate more strongly than verbal language skills with the social support components. Conclusion: Prelingual deafness has a strong impact on the course of schizophrenia. In the long run, many of these patients belong to a “minority within a minority”. Accepted: 16 July 1999     

How do Typically Developing Deaf Children and Deaf Children with Autism Spectrum Disorder Use the Face When Comprehending Emotional Facial Expressions in British Sign Language?

Facial expressions in sign language carry a variety of communicative features. While emotion can modulate a spoken utterance through changes in intonation, duration and intensity, in sign language specific facial expressions presented concurrently with a manual sign perform this function. When deaf adult signers cannot see facial features, their ability to judge emotion in a signed utterance is impaired (Reilly et al. in Sign Lang Stud 75:113–118, 1992). We examined the role of the face in the comprehension of emotion in sign language in a group of typically developing (TD) deaf children and in a group of deaf children with autism spectrum disorder (ASD). We replicated Reilly et al.’s (Sign Lang Stud 75:113–118, 1992) adult results in the TD deaf signing children, confirming the importance of the face in understanding emotion in sign language. The ASD group performed more poorly on the emotion recognition task than the TD children. The deaf children with ASD showed a deficit in emotion recognition during sign language processing analogous to the deficit in vocal emotion recognition that has been observed in hearing children with ASD.     

Handedness in schizophrenia: a quantitative review of evidence

OBJECTIVE: The prevalence of various anomalous handedness subtypes in schizophrenia patients remains ambiguous. Although current literature favours the notion that the shift in lateral preferences seen is because of an increase of mixed-handedness, several studies suggest that exclusive left handedness is more prevalent than in the general population. METHOD: Over 40 studies with reported prevalence data on various handedness subtypes in a schizophrenia population were evaluated by meta-analysis. Combined odds ratios for the three common handedness subtypes (left, mixed, and right) were separately calculated. RESULTS: Each of the three atypical hand dominance patterns were significantly greater in schizophrenia patients than in control subjects, showing that the leftward shift in handedness distribution is not entirely because of an increase in mixed-handedness alone. CONCLUSION: An increase of exclusive left-handedness is at variance with the prevailing assertion that the handedness shift in schizophrenia patients is because of a diffuse and bilateral hemispheric insult.     

Mental distress and quality of life in a deaf population

BACKGROUND: High risks of mental illness within the deaf community are reported. The assessment of the level of mental distress and quality of life in the deaf community is difficult due to communication problems in spoken and written language. The deaf community is characterized by the use of sign language. METHODS: A new measure of acceptable reliability using sign language is described. The interactive computerised package including special versions of the World Health Organisation's Brief Quality of Life questionnaire (WHOQOL-BREF), the 12-Item General Health Questionnaire (GHQ-12) and five subscales of the Brief Symptom Inventory (BSI) was administered to a large community sample of deaf people (n = 236), and results were compared with normative data for German-speaking hearing people. RESULTS: The deaf sample has a significantly poorer quality of life than the general population for the physical and psychological domains (p < 0.01) as measured by the WHOQOL-BREF. However, in the domain of social relationships, no significant difference (p = 0.19) was demonstrated. All findings with the GHQ-12 and the BSI show much higher levels (p = 0.01) of emotional distress among the deaf. CONCLUSION: Although a poorer quality of life and a higher level of mental distress are demonstrated, the similarity to the general population in the domain social relationships shows that this does not affect all domains. These findings show the need for easily accessible health services for the deaf which offer sensitive communication with them.     

Do deaf adults with limited language have advanced theory of mind?

Previous studies show that deaf children have deficits in false belief understanding due to their language impairment. However, it is not clear whether deaf adults still have problems in advanced theory of mind (ToM). The present study examined deaf adults’ performance on three aspects of advanced ToM. All of the deaf groups lacking mental state language tended to perform worse than the hearing group on explicit mental state understanding. Deaf groups with either vocabulary skill or interpersonal experience from early years were similar to the hearing group in implicit mental state reasoning. Individuals frequently using syntactic complements or having interpersonal experience with hearing people from early years tended to use ToM better. Moreover, language ability was the only predictor for explicit rather than implicit mental state understanding. Sufficient language is not necessary for all aspects of advanced ToM. Rich interpersonal experience as a substitute for language may facilitate deaf adults’ advanced ToM.