Language development in a child with left hemispherectomy

A longitudinal study of a left hemispherectomized boy (AB) was conducted to document linguistic evolution and maturation and determine the extent to which right hemisphere processes allow development of language. Resection of the left hemisphere occurred at age 5 years 6 months, following intractable epilepsy. Tests of language comprehension (pointing, understanding of prepositions, understanding of narratives) and production (naming, repetition, lexical diversity, grammatical production) were administered at ages 6:2, 6:4, 6:6, and 6 years 9 months. Observations showed little progress, if any, in most aspects of linguistic performance. In contrast to studies with left-hemispherectomized children, AB showed only a modest expansion of the semantic lexicon and the phonological repertoire more than a year after the surgical intervention. These observations indirectly suggest (1) poor functional involvement of the right hemisphere in the development of adequate linguistic abilities, (2) the necessary integrity of the LH for adequate development of language, or (3) that variations in individual brain maturation rates may account for AB's linguistic progress.     

On the representation of language in the right hemisphere of right-handed people.

Laterality experiments using reaction time were conducted to assess the performance of the right hemisphere of normal people on verbal tasks. The results show that if the task calls for pictorial encoding of visually presented verbal material, then the right hemisphere's performance is superior to that of the left. When the task calls for linguistic analysis, the minor hemisphere displays no aptitude in dealing with the task. The latter finding is at variance with data from split-brain research. To reconcile these differences, it was proposed that language functions, though represented in the right hemisphere of normal people, are functionally localized in the left. When the control which the left hemisphere exerts over the right is weakened or removed, e.g., by commissurotomy, right hemisphere language is released. The application of this model to other neurological phenomena is briefly discussed.     

Neuropsychological assessment of a case of early right hemiplegia: qualitative and quantitative analysis

Evidence for normal development of linguistic but poor visuo-perceptual skills has been obtained with the neuropsychological assessment of a case of early left-brain injury. Data suggest the transfer of linguistic functions from the left to the right hemisphere at the expense of visuo-perceptual capacities for which the right hemisphere is potentially specialized.     

The effects of right and left hemiparkinsonism on prosody

Recent studies show right hemisphere dominance in the mediation of emotional prosody and left hemisphere contribution to linguistic prosody in patients with cortical injury. The present study investigated emotional and linguistic functions of prosody as well as facial and musical processing in 21 patients with lateralized subcortical disease. Fourteen right hemiparkinsonians (RPD) and 7 left hemiparkinsonians (LPD) were compared to 17 normal controls (NC). Patients were impaired on receptive and expressive tests of emotional and linguistic prosody. Patients were also selectively impaired on emotional processing of facial stimuli and in the musical processing of pitch and tonal memory, though not timber. These findings suggest that monotone speech reported in PD is of multimodal origins and may involve dysfunction in neural centers involved in emotional and linguistic processing. There were no differences between RPD and LPD groups in the pattern of deficits, suggesting bilateral involvement in emotional processing at the subcortical level.     

How normal is grammatical development in the right hemisphere following hemispherectomy? The root infinitive stage and beyond

We examined the morphosyntax of eight left hemispherectomized children at two different stages and compared it to MLU-matched normals. We found that the language of the hemispherectomies paralleled that of their MLU matches with respect to the specific morphosyntactic characteristics of each stage. Our findings provide strong evidence for the presence of functional categories in all early grammars and demonstrate that grammatical development, regardless of its neural substrate, is highly constrained by UG and follows a narrowly determined course. We discuss our findings within a neurobiological framework in which etiology defines the integrity of the remaining hemisphere, which in turn, determines its potential for linguistic reorganization and/or acquisition.     

The corpus callosum and cerebral speech lateralization

In order to specify the callosal involvement in the establishment of cerebral lateralization, a dichotic listening task was administered to six subjects with congenital absence of the corpus callosum, two callosotomized patients, and two hemispherectomized patients. The acallosal subjects were also compared to six subjects matched for age, sex, and hand dominance as well as to six subjects also matched for IQ. Our findings indicate that language functions, as assessed by dichotic listening performance, are more strongly lateralized in callosal agenesis subjects than in IQ-matched normal controls. Our results also reveal that hemispherectomized patients typically show a strong ear-advantage favoring the ear contralateral to their remaining hemisphere. Callosotomized patients, on the other hand, show a more variable pattern of results that seems to be related to the postsurgical time interval. Finally, our findings suggest that there might be a relationship between IQ and lateralization in subjects with borderline or mild deficiency.     

Language function and dysfunction among Chinese- and English-speaking polyglots: Cortical stimulation, Wada Testing, and clinical studies

Language functions in a group of Chinese- and English-speaking polyglots living in a multiracial society have been investigated by several methods: the effects of cortical stimulation on object-naming and reading tasks in patients who required awake craniotomy, lateralization of cerebral dominance for speech by the Wada Test, and the pattern of language loss and recovery following stroke. The data indicate that these polyglots were all left hemisphere dominant for the languages tested: no consistent evidence for increased participation by the right hemisphere for language functions was found. The cortical stimulation experiments provided data most compatible with the "differential localization" model of cerebral localization in bilingualism. The variable which most influenced performance in all of these investigations was which language was used primarily for speaking as well as reading and writing at the time of the study.     

Right-hemispheric dominance for processing extended non-linguistic frequency transitions

The left hemisphere is specialized for most linguistic tasks and the right hemisphere is specialized for many non-linguistic tasks, but the cause of these functional asymmetries is unknown. One of the stimulus factors that appears to influence these asymmetries is the rate at which stimuli change. In the present experiment, 41 participants completed the Fused Dichotic Words Test (FDWT) and a non-linguistic Frequency Transition Task (FTT) wherein the Frequency Transitions (FTs) were either rapid (40 ms) or relatively slow (200 ms). There was a right hemisphere advantage for slow FTs when the change was at the front of the stimulus, but no corresponding left hemisphere advantage for the rapid FTs. There was no relationship between either FTT and the left hemisphere advantage exhibited on the FDWT. This finding provides support for the position that the right hemisphere dominates tasks that require temporal processing over relatively long periods of time.     

Left hemispheric interference with nonverbal performance in aphasics: comparison with data from split-brain studies

Two nonverbal tasks (Nebes' Figural Unification Test and Arc-Circle Matching Task) were given to 10 aphasic patients and 10 normal controls. Observations in split-brain patients have shown that the right hemisphere performs almost normally on these tasks while the left hemisphere fails completely. Left and right hand performances of aphasics and controls were compared with those of split-brain patients as reported in the literature. In the Figural Unification Test the aphasics' left hand performance was significantly poorer than that of split-brain patients. This is interpreted as an effect of left hemispheric interference with right hemispheric nonverbal performance. The lack of a similar impairment of left hand performance in the Arc-Circle Matching Task suggests that this interference is only provoked by tasks which, due to the possible verbalization of stimulus material, tend to stimulate left hemispheric activity.     

The effect of word length on hemispheric word recognition: evidence from unilateral and bilateral-redundant presentations

Visual half field studies have repeatedly demonstrated the left hemisphere's superiority for language processing. Previous studies examined the effect of word length on bilateral and unilateral performance by comparing foveal and parafoveal presentations. The present study removed the potential confound of acuity by using parafoveal presentations for both unilateral and bilateral trials. Twenty participants named 3-, 4-, 5-, and 6-letter words. The results supported previous findings, with right hemisphere performance being particularly degraded with increases in word length. There was no difference between left hemisphere and bihemispheric performance in terms of speed or accuracy, suggesting that bihemispheric performance is reliant upon the strategy of the hemisphere superior for language processing. Overall, the pattern of results supports the notion that the left hemisphere's superior linguistic capacity results from a more parallel processing strategy, while the right hemisphere is reliant upon a more sequential mechanism.     

Unilateral brain lesions in childhood: performance on the Revised Token Test

Comprehension of connected language as assessed by the Revised Token Test (RTT) was studied in 17 children with left hemisphere lesions (LL) and 11 with right hemisphere lesions (RL). LL children's significantly lower performance on several subtests than left controls (LC) matched by age, sex, race, and social class appeared to be related to the memory demands of these subtests rather than the limited syntactic elements assessed by the RTT. LL subjects requested significantly more command repetitions than control or RL subjects and when a repetition was not requested LL subjects often responded with immediacy. Although RL children tended to perform lower than right matched controls (RC), these differences were not significant nor readily related to either the memory or specific linguistic structures assessed. RL subjects required fewer command repetitions than LL subjects and exhibited a significantly greater frequency of immediate responses than controls or LL subjects. While based on few children, a trend for LL children with retrorolandic lesions to perform more poorly than those with left prerolandic lesions was suggested. No systematic difference in performance was apparent for children with left cortical vs. left subcortical lesions or among discrete sites of lesions within the right hemisphere. Children with left lesions prior to 1 year of age performed no better and, in several instances, significantly poorer than LL patients sustaining lesions after 1 year of age. Among RL subjects, those sustaining lesions after 1 year of age had greater difficulty than those with lesion onset before 1 year of age, especially on linguistic elements which seemed to be dependent upon visual spatial properties. Further studies are needed to evaluate the comprehension of more complex linguistic structures among children with unilateral brain lesions as well as to study the role of more basic factors such as memory and attention in explaining the present findings.     

Language Development in Children with Simple-Partial Left-Hemisphere Epilepsy

The nature of cerebral involvement in the acquisition of language was addressed in this longitudinal study of children with an early diagnosis of epilepsy with simple-partial seizures (SPE) and with epileptogenic foci localized in the left frontal (LF) lobe. Yearly evaluations of six SPE-LF children on tests of linguistic comprehension (pointing, understanding of narrative, and understanding of prepositions) and production (repetition, lexical diversity, and grammatical production) were carried out between the ages of 3 and 8 years and compared to those of large samples of control children on the same tasks and at each age level. Linguistic production of all children were transcribed, coded, and analyzed using the Child Language Data Exchange System (MacWhinney & Snow, 1991). Individual evolution trajectories revealed that SPE-LF children showed a clear dissociation in linguistic performance between comprehension and production. Linguistic comprehension gradually improved to reach normal performance levels by age 7 while linguistic production, even at later stages, remained quite poor. This dissociation in the development of linguistic performance in SPE-LF children suggests a complex interplay between brain maturation dynamics and dysfunction modulating the succession of stages in language development. The observed persistent deficits in specific aspects of linguistic performance argue for an early involvement of the anterior areas of the left cerebral hemisphere in the production of language.     

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.     

Intermanual transfer of prism adaptation

The authors measured intermanual transfer in participants (N = 48) whose exposed or unexposed right or left hand was tested 1st after participants experienced prismatic displacement. Test order did not affect either participants' performance during prismatic exposure or the usual aftereffects, but transfer occurred only when the authors tested the exposed right hand 1st. Transfer did not occur, and proprioceptive shift for the exposed left limb decreased when the authors tested the unexposed right limb 1st. The present results suggest that transfer occurs during testing for aftereffects of prism exposure, but not during prism exposure itself, as researchers have previously assumed. Results are consistent with those of previous research that has shown that limb control is lateralized in opposite hemispheres and that the left hemisphere contains a spatial map only for the right limb.     

Speech-Language Outcomes of Hemispherectomy in Children and Young Adults

Children and young adults who had undergone right or left hemispherectomy for intractable seizures after a period of normal language acquisition were compared with respect to scores on speech and language tests. The majority of the subjects had full scale IQs in the borderline to mentally retarded range. Language scores were computed in relation to estimated mental age, not chronological age. On this basis, the left hemispherectomized children were more likely to show syntactic comprehension and rapid-rate auditory processing deficits than the right hemispherectomized. The two groups were similar to one another and to normal children in speech production. The findings are discussed in relation to developmental language disorders.     

Complementarity of Linguistic and Prosodic Processes in the Intact Brain

Despite considerable speculation in the research literature regarding the complementarity of functional lateralization of prosodic and linguistic processes in the normal intact brain, few studies have directly addressed this issue. In the present study, behavioral laterality indices of emotional prosodic and traditional linguistic speech functions were obtained for a sample of healthy young adults, using the dichotic listening method. After screening for adequate emotional prosody and linguistic recognition abilities, participants completed the Fused Rhymed Words Test (FRWT; Wexler & Halwes, 1983) and the Dichotic Emotion Recognition Test (DERT; McNeely & Netley, 1998). Examination of the difference in ear asymmetries for these measures within individuals revealed a complementary pattern in 78% of the sample. However, the correlation between laterality quotients for the FRWT and DERT was near zero, supporting Bryden's model of "statistical" complementarity (e.g., Bryden, 1990).     

攻击行为儿童大脑半球某些认知特点的研究

为了解攻击行为儿童大脑两半球的认知活动特点,采用侧视野速示呈现技术,对径“同伴提名量表”筛选的１７名攻南 儿童和１６名正常儿童进行了比较研究。     

Duplex perception: some initial findings concerning its neural basis

Duplex perception is the simultaneous perception of a speech syllable and of a nonspeech "chirp," and occurs when a single formant transition and the remainder (the "base") of a synthetic syllable are presented to different ears. The current study found a slight but nonsignificant advantage for correct labeling of the fused syllable when the chirp was presented to the left ear. This advantage was amplified in the performance of a "split-brain" subject. A subject with a left pontine lesion performed at chance level when the chirp was presented to her left ear. These findings suggest that some, if not complete, ipsilateral suppression does occur in the dichotic fusion procedure, and that identification of the fused syllable is maximal when the left hemisphere fully processes the linguistic characteristics of the base (through contralateral presentation), and at least minimally processes the frequency transition information of the chirp (through ipsilateral presentation).     

Encouraging pointing with the right hand,but not the left hand,gives right-handed 3-year-olds a linguistic advantage

Previous research has shown a strong positive association between right-handed gesturing and vocabulary development. However, the causal nature of this relationship remains unclear. In the current study, we tested whether gesturing with the right hand enhances linguistic processing in the left hemisphere, which is contralateral to the right hand. We manipulated the gesture hand children used in pointing tasks to test whether it would affect their performance. In either a linguistic task (verb learning) or a non-linguistic control task (memory), 131 typically developing right-handed 3-year-olds were encouraged to use either their right hand or left hand to respond. While encouraging children to use a specific hand to indicate their responses had no effect on memory performance, encouraging children to use the right hand to respond, compared to the left hand, significantly improved their verb learning performance. This study is the first to show that manipulating the hand with which children are encouraged to gesture gives them a linguistic advantage. Language lateralization in healthy right-handed children typically involves a dominant left hemisphere. Producing right-handed gestures may therefore lead to increased activation in the left hemisphere which may, in turn, facilitate forming and accessing lexical representations. It is important to note that this study manipulated gesture handedness among right-handers and does therefore not support the practice of encouraging children to become right-handed in manual activities.

Research Highlights

• Right-handed 3-year-olds were instructed to point to indicate their answers exclusively with their right or left hand in either a memory or verb learning task.
• Right-handed pointing was associated with improved verb generalization performance, but not improved memory performance.
• Thus, gesturing with the right hand, compared to the left hand, gives right-handed 3-year-olds an advantage in a linguistic but not a non-linguistic task.
• Right-handed pointing might lead to increased activation in the left hemisphere and facilitate forming and accessing lexical representations.

     

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.