Abstracts

Abstract

The intracarotid amobarbital procedure (IAP) was conducted with a profoundly deaf young man prior to right anteromedial temporal lobectomy for pharmacologically refractory partial complex seizures. The IAP required considerable modification in order to take into account the use of varying sign language methods and related issues. Visual memory, American Sign Language, signed English, and finger-spelling functioning were all assessed. The patient manifested left hemisphere dominance for all these abilities, performing well under right hemisphere anesthesia. In contrast, no ability to function on these tasks was detectable when the left hemisphere was anesthetized. This demonstrates that an intact left temporal lobe and related structures are sufficient to support sign language functioning. The development of a deaf adaptation of the IAP is of methodological significance, as the IAP is thereby rendered accessible for deaf patients.     

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.     

Contrastive patterns of intrahemispheric interference to verbal and spatial concurrent tasks in right-handed, left-handed and stuttering populations

A time-sharing paradigm was used to assess hemispheric lateralization for both language and visuo-spatial processing in right-handed, left-handed and stuttering populations. A right hand only tapping disruption, indicative of left hemisphere interference, accompanied concurrent verbal tasks only in the dextral group. Left-handers and stutterers revealed symmetrical patterns of hemispheric language interference. Significantly different absolute levels of language interference were found for the three groups, with dextrals having the least, followed by sinistrals, and being greatest for stutterers. These magnitude differences were explained in relation to a hypothesis of strength of language representation within a given hemisphere. Visuo-spatial right hemisphere interference was shown for left-handers with a concurrent object chimera task.     

Evidence of minimal cerebral asymmetries for the processing of English words and American sign language in the congenitally deaf

Previous investigators reported that auditory association cortex is usually larger within the left than within the right hemisphere, even in the newborn. They suggested that this asymmetry could play a causal role in the predominant tendency for language processes to lateralize in the left rather than in the right hemisphere. For congenitally deaf persons, however, the role of auditory association area asymmetry presumably would be nullified. This question was addressed by comparing the performances of congenitally deaf college students and hearing persons on lateralized tachistoscopic tasks thought to reflect hemispheric language and spatial processing efficiencies. The results indicated that indicated that congenitally deaf Ss showed minimal half-field asymmetries for both English word stimuli and for American Sign Language stimuli (drawings of hand configurations representing letters and words for the deaf Ss). Results were interpreted as supporting auditory experience as a major determinant of cerebral functional asymmetries and as contradictory to clinical reports that had suggested that the cerebral organization of “communicative” functions were entirely comparable in deaf and hearing persons.     

Zur hemispha¨rendominanz fu¨r sprache und rechnen: Elektrophysiologische korrelate einer linksdominanz bei linksha¨ndern

Slow brain potentials were recorded in left-handers and right-handers during: (i) processing of language and mental arithmetic tasks, without vocalization, and (ii) subsequent writing down of the answers with either the right or left hand. Left-sided laterality of negative potentials was taken as evidence of hemispheric dominance. It appeared during the processing of words and numbers in 26 of the 30 left-handers and was localized mainly in the left frontal and temporal parietal regions. Similar results were found with the right-handers. This electrophysiological evidence indicates that the left hemisphere is dominant for language and calculation in the vast majority of left-handers. Only when writing with either their left or right hand do left-handers show less left-sided laterality than right-handers.     

Hemispheric dominance for speech and calculation: electrophysiologic correlates of left dominance in left handedness

Slow brain potentials were recorded in left-handers and right-handers during: (i) processing of language and mental arithmetic tasks, without vocalization, and (ii) subsequent writing down of the answers with either the right or left hand. Left-sided laterality of negative potentials was taken as evidence of hemispheric dominance. It appeared during the processing of words and numbers in 26 of the 30 left-handers and was localized mainly in the left frontal and temporal parietal regions. Similar results were found with the right-handers. This electrophysiological evidence indicates that the left hemisphere is dominant for language and calculation in the vast majority of left-handers. Only when writing with either their left or right hand do left-handers show less left-sided laterality than right-handers.     

A case of ‘sign blindness’ following left occipital damage in a deaf signer

We report on a right-handed, deaf, life long signer who suffered a left posterior cerebral artery (PCA) stroke. The patient presented with right homonymous hemianopia, alexia and a severe sign comprehension deficit. Her production of sign language was, however, virtually normal. We suggest that her syndrome can be characterized as a case of ‘sign blindness’, a disconnection of the intact right hemisphere visual areas from intact left hemisphere language areas. This case provides strong evidence that the neural systems supporting sign language processing are predominantly in the left hemisphere, but also suggests that there are some differences in the neural organization of signed vs spoken language within the left hemisphere.     

Neural basis of action understanding: Evidence from sign language aphasia

Background: The neural basis of action understanding is a hotly debated issue. The mirror neuron account holds that motor simulation in fronto-parietal circuits is critical to action understanding including speech comprehension, while others emphasise the ventral stream in the temporal lobe. Evidence from speech strongly supports the ventral stream account, but on the other hand, evidence from manual gesture comprehension (e.g., in limb apraxia) has led to contradictory findings.

Aims: Here we present a lesion analysis of sign language comprehension. Sign language is an excellent model for studying mirror system function in that it bridges the gap between the visual–manual system in which mirror neurons are best characterised and language systems which have represented a theoretical target of mirror neuron research.

Methods & Procedures: Twenty-one life-long deaf signers with focal cortical lesions performed two tasks: one involving the comprehension of individual signs and the other involving comprehension of signed sentences (commands). Participants’ lesions, as indicated on MRI or CT scans, were mapped onto a template brain to explore the relationship between lesion location and sign comprehension measures.

Outcomes & Results: Single sign comprehension was not significantly affected by left hemisphere damage. Sentence sign comprehension impairments were associated with left temporal–parietal damage. We found that damage to mirror system related regions in the left frontal lobe were not associated with deficits on either of these comprehension tasks.

Conclusions: We conclude that the mirror system is not critically involved in action understanding.     

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.     

Language lateralization in a bimanual language

Unlike spoken languages, sign languages of the deaf make use of two primary articulators, the right and left hands, to produce signs. This situation has no obvious parallel in spoken languages, in which speech articulation is carried out by symmetrical unitary midline vocal structures. This arrangement affords a unique opportunity to examine the robustness of linguistic systems that underlie language production in the face of contrasting articulatory demands and to chart the differential effects of handedness for highly skilled movements. Positron emission tomography (PET) technique was used to examine brain activation in 16 deaf users of American Sign Language (ASL) while subjects generated verb signs independently with their right dominant and left nondominant hands (compared to the repetition of noun signs). Nearly identical patterns of left inferior frontal and right cerebellum activity were observed. This pattern of activation during signing is consistent with patterns that have been reported for spoken languages including evidence for specializations of inferior frontal regions related to lexical-semantic processing, search and retrieval, and phonological encoding. These results indicate that lexical-semantic processing in production relies upon left-hemisphere regions regardless of the modality in which a language is realized, and that this left-hemisphere activation is stable, even in the face of conflicting articulatory demands. In addition, these data provide evidence for the role of the right posterolateral cerebellum in linguistic-cognitive processing and evidence of a left ventral fusiform contribution to sign language processing.     

Hemispheric control of the writing hand: the effect of callosotomy in a left-hander

We report a case of a left-hander with left hemispheric language. After callosotomy, he could use the left hand to write only random letters and digits, and he became right-handed for writing. Therefore, writing by left-handers with left hemispheric language dominance may be accomplished by transcallosal transmission of the linguistic content from the left hemisphere to the right.     

Attention to central and peripheral visual space in a movement detection task. III. Separate effects of auditory deprivation and acquisition of a visual language

We employed event-related brain potentials (ERPs) and measures of signal detectability to compare attention to peripheral and central visual stimuli in normal hearing subjects who were born to deaf parents (HD Ss) and whose first language was American Sign Language (ASL). The results were compared with those obtained from normal hearing Ss and congenitally deaf Ss in the same paradigm. Task performance and ERPs during attention to the foveal region were similar in the 3 groups. In contrast, with attention to the peripheral stimuli the deaf Ss displayed attention effects over the occipital regions of both hemispheres that were several times larger than those in the hearing and the HD Ss. However, both HD and deaf Ss displayed lateral asymmetries in behavior and ERPs that were opposite in direction to those of the hearing Ss. Whereas hearing Ss detected the direction of target motion better when it occurred in the left visual field, deaf and HD Ss performed better for right visual field targets. Consistent with these results, the amplitude of the attention-related increases in the ERPs were larger from temporal and parietal regions of the right than the left hemisphere in hearing Ss, but were larger from the left than the right hemisphere in both the HD and the deaf Ss. These results suggest that auditory deprivation and the acquisition of a visual language have marked and different effects on the development of cortical specializations in humans.     

Inverted handwriting position,language laterality,and the Levy-Nagylaki genetic model of handedness and cerebral organization

Levy's hypothesis that left-handers who employ an “inverted” handwriting position (the pen being pointed toward the writer's body) are left hemisphere dominant for language functions was tested by assessing the relationship of the inverted and noninverted writing styles to dichotic and lateralized tachistoscopic indices of hemispheric language specializations. Results failed to show any difference in the degree of left hemisphere language dominance for the two writing position groups. It also was found that males employed the inverted hand position significantly more often than females. Both findings cast doubt on the validity of the Levy-Nagylaki genetic model of left-handedness and the cerebral organizations of the left- handed.     

Motor control of the hands: the effect of familial sinistrality.

Left- and right-handed subjects, selected on the basis of degree of hand preference and for the presence or absence of familial sinistrality, responded to monaurally presented tonal stimuli (440 Hz note played on four different instruments) using their right and left hands on separate occasions. It was found that in both the strong left-handers and the inconsistent strong right-handers, motor control of the hands was related to familial sinistrality (FS). Specifically, strong left-handers and inconsistent strong right-handers with FS have a difference in the motor control of the hands in the left hemisphere, with a left hemisphere-left hand advantage. Strong left-handers and inconsistent strong right-handers with no FS have a difference in the motor control of the hands in the right hemisphere, with a right hemisphere-left hand advantage.     

Lateralization of language and spatial functions in left-handed populations.

The level of performance in the execution of a tactual-linguistic task was studied in two left-handed populations, one with language lateralized to the left and the other with language lateralized to the right hemisphere, according to Kimura's dichotic digit test. The results showed that left-handers with speech most likely lateralized to the left hemisphere performed significantly better in the tactual-linguistic task with the left hand, while the ones with speech probably lateralized to the right hemisphere, did better with the right hand. The data suggest that integration of functions asymmetrically represented is facilitated by their differential lateralization.     

Mirror writing, left-handedness, and leftward scripts

This minireview concerns a new observation on mirror writing. An uncommon form of writing, mirror writing is seen among healthy individuals, but it can also follow a variety of neurological diseases; it is nearly always carried out with the left hand and is more easily undertaken by left-handers. We have found that a particularly high prevalence of left-handed mirror writing has been reported among those whose native languages are traditionally written in a leftward direction, including Chinese, Japanese, and Hebrew. Innate left-handers and those whose languages are written leftward thus share an unusual facility for left-handed mirror writing, an observation that may have implications for understanding hemisphere specialization in relation to handedness.     

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.     

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.     

DIRECTION OF HAND PREFERENCE: THE CONNECTION WITH SPEECH AND THE INFLUENCE OF FAMILIAL HANDEDNESS

Taking familial handedness into account, right- and left-handers with differing degrees of hand preference were monaurally presented with verbal stimuli (CVs) to which they responded using their right and left hands at separate times. This reaction time design was used to ascertain the relative cognitive functioning capacity of each hemisphere for verbal processing. However, the results disclosed more about the determination of direction of hand preference than about cognitive processing, per se. It was found that in both strong right-handers and strong left-handers with an incongruent hand preference (i.e., own handedness incongruent with family history of handedness) direction of hand preference is the result of suppression of the nonpreferred hand in the left hemisphere. Strong right- and strong left-handers with a congruent hand preference (i.e., hand preference congruent with family history of handed ness) appear to have a more direct hand preference-left hemisphere mechanism. The findings of the present study are used to form part of a new theory of hand preference determination.