Cerebral lateralization of deaf and hearing individuals for linguistic comparison judgments.

A group of congenitally deaf adults and a group of hearing adults, both fluent in sign language, were tested to determine cerebral lateralization. In the most revealing task, subjects were given a series of trials in which they were fist presented with a videotaped sign and then with a word exposed tachistoscopically to the right visual field or left visual field, and were required to judge whether the word corresponded to the sign or not. The results suggested that the comparison processes involved in the decision were performed more efficiently by the left hemisphere for hearing subjects and by the right hemisphere for deaf subjects. However, the deaf subjects performed as well as the hearing subjects in the left hemisphere, suggesting that the deaf are not impeded by their auditory-speech handicap from developing the left hemisphere for at least some types of linguistic processing.     

Cerebral lateralization for speech in deaf and normal children

The cerebral lateralization pattern for speech production in normal hearing and congenitally deaf children was studied using the dual-task paradigm. Performance under the verbal task conditions showed predicted left hemispheric dominance for speech production in the normal hearing children. No developmental trends in asymmetry were found, suggesting that speech lateralization is present in normal 3-year-old children. These data support the developmental invariance hypothesis of cerebral organization. Deaf children showed more symmetrical patterns of cerebral control for speech production. No developmental trends in functional brain organization were observed among prepubescent deaf children.     

视觉语言对听觉障碍人群阅读能力的影响及作用机制

听觉障碍人群由于听觉部分或完全受损, 视觉语言——唇读和手语就成为其阅读能力发展的主要途径。唇读有助于听觉障碍人群形成语音表征, 与词汇知识相互影响, 且可以促进字词阅读及阅读理解的水平; 口语或书面语的加工可以激活相应的手语表征, 手语影响着听觉障碍人群各个层次的阅读能力。未来研究应该关注语音意识、词汇知识等技能在视觉语言影响听觉障碍人群阅读能力过程中的作用机制, 并以视觉语言为中心, 发展出适合汉语听觉障碍人群阅读能力习得的理论模型。     

Lateral-frontal slow potential shifts preceding language acts in deaf and hearing adults

Slow potential EEG shifts (SPSs) recorded over Broca's area and the paired contralateral site preceding cued language acts have been reported to identify the language-dominant hemisphere. A contingent negative variation paradigm SPS method was applied to the comparative study of 10 hearing adults and of 10 adult prelingually deaf persons whose first learned language was American Sign Language. Volunteers performed both language and non-language acts in both oral and manual expressive modes. The hearing group showed no lateralized SPS, failing to replicate previous reports. The deaf group showed a nonsignificant trend opposite in laterality to that of hearing groups in previous reports.     

The effects of linguistic experience on cerebral lateralization for speech production in normal hearing and deaf adolescents

The cerebral lateralization patterns for speech production in 57 normal hearing and deaf adolescents were studied using the dual-task paradigm. Normal hearing subjects showed left hemispheric dominance for speech production, whereas both the congenitally deaf and those with early acquired deafness showed atypical cerebral representation for speech production. Deaf subjects whose hearing loss occurred after 2 years of age displayed a pattern of mixed cerebral dominance related to complexity of speech production or task difficulty. These results are interpreted as evidence for a relationship between linguistic/cognitive stage of development and the ontogenesis of cerebral lateralization. A parallel lateralization hypothesis of left cerebral dominance for speech production is offered.     

Sign language as cognition for deaf people: Pitfalls and prospects

With a tradition reliance on verbal paradigms cognitive psychology has repeatedly rediscovered the centrality of verbal processes in the cognitive representation of the world. Frequently it has been considered that non-speaking groups offer the proof of such psychological theories. Deaf people, because of their apparently poor memory, retardation in reading, relative lack of speech, yet cognitive viability, have offered an ideal test population for cognitive paradigs. Unfortunately deaf people turn out not to be a non linguistic control. We have now discovered sign language—a visual, spatial representation form used naturally by profoundly deaf people. This apparently offers the key the deaf people's cognition without speech. This paper describes some aspects of what we know of deaf people and their language, critically examines some of the evidence for sign representation in memory, and discusses the methodological problems to be faced by anyone searching for conclusive evidence on deaf people's working memory. Despite the attractiveness of ‘sings for words’ in cognition, this paper argues that the evidences is weak and signs may not be equated easily with words.     

Cerebral lateralization in simultaneous interpretation

Cerebral asymmetries for L1 (Italian), L2 (English), and L3 (French, German, Spanish, or Russian) were studied, by using a verbal-manual interference paradigm, in a group of Italian right-handed polyglot female students at the Scuola Superiore di Lingue Moderne per Interpreti e Traduttori (SSLM-School for Interpreters and Translators) of the University of Trieste and in a control group of right-handed monolingual female students at the Medical School of the University of Trieste. In an automatic speech production task no significant cerebral lateralization was found for the mother tongue (L1) either in the interpreting students or in the control group; the interpreting students were not significantly lateralized for the third language (L3), while weak left hemispheric lateralization was shown for L2. A significantly higher degree of verbal-manual interference was found for L1 than for L2 and L3. A significantly higher disruption rate occurred in the meaning-based mode of simultaneous interpretation (from L2 into L1 and vice versa) than in the word-for-word mode (from L2 into L1 and vice versa). No significant overall or hemispheric differences were found during simultaneous interpretation from L1 into L2 or from L2 into L1.     

Cerebral lateralization and reading dysfunction

The laterality preference patterns and types of oral reading errors were examined for 90 seventh-grade males. Specifically, scores on a self-report measure of lateral preference for 30 readers with adequate decoding skills but low comprehension and 30 readers who lacked decoding skills were compared with each other and with 30 good readers. As predicted, poor readers with grade appropriate word recognition scores were found to be generally more confused in their lateral preference than were good readers or poor readers who lacked decoding skills. Results of oral reading errors confirmed a visual integration problem for the more bilateral reader. Poor comprehenders with word recognition skills also reported significantly greater mixed lateral patterns for their fathers than did other readers. The results were interpreted as supporting the initial argument that difference-poor readers fail to comprehend because of problems in organizing visual input, which seems intimately tied to a bilateralization of functions.     

The interplay between early social interaction,language and executive function development in deaf and hearing infants

In this article, we review the influence of early social interaction on the development of executive function and language in infants. We first define social interaction, executive function and language and show how they are related in infant development. Studies of children born deaf are used to illustrate this connection because they represent cases where there has been a disruption to early social interaction and the development of intersubjectivity. Unlike other groups, the disturbance to development is known to be largely environmental rather than neuro-biological. This enables us to more accurately tease apart those impacts on EF that are associated with social interaction and language, since the potential confounds of disordered cognitive development are largely controlled for. The review offers a unifying model for how social, cognitive and linguistic development work together in early human development.     

Tactile gap detection and language lateralization

Recent work suggests that hemispheric language lateralization might be related to the fine-grained temporal discriminations that are required for linguistic processing (Nicholls, 1996). Studies concerning tactile processing have also shown a significant left-hemisphere (L-H) advantage for tactile gap detection (Nicholls & Whelan, 1997). We hypothesized that language and tactile processing are both preferentially processed by the left hemisphere because it is specialized for tasks requiring fine-grained temporal resolution. Thirty-two participants (16 right and 16 left handers) were tested for both linguistic processing (using the Fused Dichotic Words Test (FDWT)) and tactile gap detection. Both right and left handers showed a significant L-H advantage for both language processing and tactile gap detection. The present study supports recent claims that language lateralization is attributable to the left hemisphere's better suitability to process tasks that require fine-grained temporal resolution.     

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.     

Left hemisphere language lateralization in bilinguals and monolinguals

Tachistoscopic studies of lateralization in bilinguals suggest that there is a greater degree of right hemisphere involvement in their processing of language than is typically found in monolinguals. However, most of the studies reviewed failed to control the sex, handedness, and degree of fluency of the subjects and did not include a monolingual comparison group. The present study used adult right-handed males (Portuguese-English bilinguals and English-speaking monolinguals) in a tachistoscopic word-reading task. In Experiment 1, the words from the bilinguals’ two languages were presented in mixed blocks, while in Experiment 2, they were presented in separate blocks. The results were: (1) a similar level of left hemisphere advantage for language in the bilingual and the monolingual groups, (2) no evidence of greater heterogeneity of asymmetry patterns in bilinguals, and (3) a significant correlation (r=.61) for lateralization levels of the bilinguals’ two languages. These results indicate that language is processed primarily in the left hemisphere of both bilinguals and monolinguals.     

Communication and language in severely deaf adolescents

One of the most important psychological effects of early severe or profound deafness is an impairment in natural language-processing ability, with a consequent reduction in communicative skill secondary to the sensory deficit. Prelingual damage blocks the development of certain sequential/syntactical skills necessary for the acquisition of normal linguistic competence. Educators of the deaf in the UK have typically attempted to improve linguistic ability using amplification and intensive training in lip-reading, but evidence from several psychological studies suggests that communication systems based upon manual signing are more productive of both linguistic and basic cognitive skills. This paper reports an experimental study of the communicative characteristics of both oral and total communication systems as a function of language structure. For almost all types of structure investigated, the total system was found to be the more effective method of communication.     

Differences in language performance in variations of lateralization

Language proficiency was studied in 489 primary-school-aged children classified as extreme left-, extreme right-, mild left-, and mild right-handers on the basis of both hand-preference and hand-skill, using a test battery of seven measures. An ANOVA run on factor scores showed neither significant association of language proficiency with variations of lateralization regarding hand-preference and hand-skill nor differences in factor structure derived from a principal component analysis between extreme vs. mild hand-preference and hand-skill groups. Moreover, low language proficiency was not significantly associated with specific patterns of lateralization in hand-preference subgroups. In contrast, low language performers with poor hand-skill were significantly overrepresented both in the extreme left-handed group alone and when combined with the extreme right-handed, in comparison to mild left- and mild right-handed with respect to population. The data are not consistently accommodated by the theory of balanced polymorphism (mainly Annett, 1978, 1985 Annett & Manning, 1989 ). Alternately, factors such as lag of maturation ( Bishop, 1980, 1984, 1990a, 1990b ), delay of growth ( Geschwind & Galaburda, 1985b ), and developmental instability associated with unique patterns of variations in lateralization ( Yeo, Gangestad, & Daniel, 1993 ) are discussed as possible factors accounting for the present results.     

Reproducibility of fMRI-determined language lateralization in individual subjects

This study investigated within-subject test-retest reproducibility (i.e., reliability) of language lateralization obtained with fMRI. Nine healthy subjects performed the same set of three different language tasks during two fMRI sessions on separate days (verb generation, antonym generation, and picture naming). A fourth task analysis was added in which the three tasks were analyzed conjointly (combined task analysis, CTA). The CTA targets brain areas that are commonly used in different language tasks, aiming more selectively at language-critical structures. The number of active voxels (i.e., robustness) and calculated lateralization index (LI) were compared across sessions, tasks, subjects, and two a priori defined volumes of interest (classical language regions versus whole hemisphere) for a wide range of statistical thresholds. Robustness and reliability strongly varied between task analyses. The CTA was a robust detector of language-related brain activity, in contrast to the single task approaches. The CTA and verb generation task allowed for reliable calculation of the LI. Higher thresholds yielded a clear increase in left lateralization, which was largest when calculated from active voxels in classical language regions.