Functional asymmetry in schizophrenic patients during auditory speech processing

In two experiments, functional laterality and interhemispheric transfer was investigated in schizophrenic patients (n=14) and healthy controls (n=17). In Experiment 1, words and pseudowords were presented either to the left or right ear (monaural condition) or simultaneously to both ears (binaural condition). In Experiment 2, subjects had to discriminate two tones differing in frequency during monaural and binaural stimulation.Healthy controls showed a right ear advantage (REA) for word stimuli, indicating left-hemispheric superiority for word processing. The same lateralization pattern was found in schizophrenic patients, indicating unimpaired functional lateralization of auditory language processing. In both groups, no REA was found for pseudowords resulting in significant WordnessxEar interactions. When presented binaurally, auditory processing of words and pseudowords did not differ significantly from any of the two monaural conditions. Tone discrimination did not lead to any ear asymmetry. The results show normal patterns of functional asymmetry during auditory language processing and tone discrimination in schizophrenic patients.     

Interhemispheric cooperation for familiar but not unfamiliar face processing

Evidence for interhemispheric cooperation during language processing has been demonstrated for words, but not for meaningless pseudowords. Specifically, responses were found to be faster and more accurate when identical copies of a word were presented bilaterally to both hemispheres, relative to unilateral single presentations. This bilateral advantage for words seems to be a robust effect in normals. The present study addressed the question of whether the bilateral advantage is restricted to lexical material or whether it is a more global phenomenon occurring for meaningful material in general. Thirty healthy participants performed a familiarity decision in which one copy of familiar and unfamiliar faces was presented tachistoscopically to the right visual hemifield (RVF), the left visual hemifield (LVF) or simultaneously to both visual hemifields (bilateral condition, BVF). We obtained a highly significant familiarity by visual field interaction(P < 0.006) showing that only for familiar faces, a bilateral advantage was obtained. Unfamiliar face processing did not yield a bilateral advantage. We conclude that interhemispheric cooperation only occurs for meaningful material for which cortical representations can be assumed.     

Hemispheric lateralization of spatial attention in right- and left-hemispheric language dominance

Hemispheric lateralization of the neural systems supporting language and spatial attention most commonly dissociate in healthy individuals. However, the reverse pattern with association of language and attention within the right hemispheres has also been observed. We investigated in 75 healthy volunteers (37 right-handed, 38 left-handed) if language and spatial attention may associate not only in individuals with an atypical pattern of language lateralization, but also in subjects showing the standard, i.e. left-hemispheric dominance for language. Hemispheric lateralization of cerebral perfusion was determined with functional transcranial Doppler ultrasonography during a visuospatial attention, and a word generation task. We found that language and visuospatial attention associated within the left hemisphere in five subjects and within the right hemisphere in eight subjects. We conclude that all combinations of cerebral lateralization for language and attention may exist in the healthy brain.     

精神分裂症患者大脑两半球功能协同异常研究

目的：探索精神分裂症患者大脑两半球功能协同异常。方法：对20例以阳性症状为主的男性精神分裂症患者和20名男性正常人进行对照,采用两耳分听技术分别测验大脑两半球在刺激驱动条件（自动加工）和指令驱动条件（控制加工）时的注意与执行功能。结果：在刺激驱动条件下,精神分裂症患者表现为两耳分听汉语单字词的左耳（右半球）优势,而正常人则为右耳（左半球）优势;在注意左耳或右耳时患者的被注意耳的成绩虽有明显提高,但对另一侧耳刺激信息加工的抑制能力与正常人相比明显减弱,差异显著。结论：精神分裂症患者两半球功能协同有障碍,其大脑功能一侧化异常,可能与此有关。     

Language activation distributions revealed by fMRI in post-operative epilepsy patients: differences between left- and right-sided resections

OBJECTIVE: To reveal differences of cerebral activation related to language functions in post-operative temporal lobe epilepsy (TLE) patients. METHODS: Right (RTL) and left temporal lobe (LTL) resected patients, and healthy controls were studied using functional magnetic resonance imaging (fMRI). Only patients with complete left-hemispheric language dominance according to the intracarotid amytal procedure (IAP) were included. Language-related activations were evoked by performing word generation and text reading language tasks. Activation lateralization and temporo-frontal distribution effects were analysed. RESULTS: For word generation, only LTL patients showed reduced left lateralized activation compared to controls, due to a decrease in activation in the left prefrontal cortex and an increase in the right prefrontal cortex. For reading, the left-hemispheric lateralization in RTL patients increased because of enhanced activity in the left prefrontal cortex, whereas for LTL patients the activation became bilaterally distributed over the temporal lobes. Lateralization results between pre-operative IAP and post-operative fMRI were highly discordant. Significant temporo-frontal distribution changes manifested from the reading but not from the word generation task. CONCLUSION: The cerebral language representation in post-operative LTL epilepsy patients is more bi-hemispherically lateralized than in controls and RTL patients. Post-operative temporo-frontal and interhemispheric redistribution effects, involving contralateral homologous brain areas, are suggested to contribute to the cerebral reorganisation of language function.     

Recognition of emotions in facial expression of visual half-field images by schizophrenic and depressed patients]

Twenty schizophrenics, 20 depressives, and 20 normal controls were asked to identify positive and negative emotional expressions of faces tachistoscopically presented to the left and/or right visual hemifields. Results replicated the frequently cited recognition advantage for emotional stimuli presented in the left visual hemifield (right hemispheric processing). A significant reduction in decoding advantage was observed in both patient groups, which could be explained in terms of an interhemispheric disconnection syndrome in schizophrenics and depressives. Bilateral findings in particular tend to support this hypothesis, since they revealed that both cerebral hemispheres processed contrary information simultaneously.     

Stronger left-hemisphere lateralization in older versus younger adults while processing conventional metaphors

Thirty younger (age 20–30) and 30 older (age 69–85) right-handed Hebrew speakers performed a semantic judgement task while processing literal word pairs and conventional metaphors, presented in the divided visual field paradigm. Older adults responded more accurately to conventional metaphors in the right visual field/left hemisphere versus the left visual field/right hemisphere, whereas younger adults showed no lateralization. Vocabulary scores cancelled group differences in lateralization. An additional lexical decision task replicated the main finding of left-hemisphere lateralization in older but not in younger participants. We suggest that accumulated knowledge increases left-hemisphere lateralization on tasks of language comprehension in older relative to younger adults.     

Symmetrical hemispheric priming in spatial neglect: A hyperactive left-hemisphere phenomenon?

Hemispheric rivalry models of spatial neglect suggest that the left hemisphere becomes hyperactive following right-hemisphere lesions since the two hemispheres normally exert an inhibitory influence on each other via callosal connections. Using a masked hemifield priming paradigm, we investigated whether the putative change in hemispheric balance involves other, higher-order abstract representational systems in spatial neglect. Participants consisted of 12 neglect patients with right-hemisphere damage and three groups of control participants, i.e., 12 young healthy controls, 10 age-matched healthy controls and 10 right-hemisphere patients without spatial neglect. In each trial, participants made semantic categorization about a centrally presented target word which was preceded by a masked prime flashed either to the left or right visual field. All three control groups exhibited strong left-hemisphere advantage in inhibitory syllabic priming, consistent with the known left-hemisphere dominance in lexical inhibition during reading. By contrast, neglect patients exhibited a symmetrical pattern of priming between the left and right visual fields. These results suggest that (1) the neglected hemifield can rapidly extract abstract information even from weak and normally non-perceptible visual stimuli, but that (2) the normal left hemispheric dominance in reading is absent in neglect patients probably because of the generalized hyperactivity of the left hemisphere. Our results demonstrate a covert behavioral change in spatial neglect which may reflect the altered inter-hemispheric balance in the bilateral word recognition system encompassing lexico-semantic memory.     

Assessing effects of stimulus orientation on perception of lateralized words and nonwords

Numerous studies of the processes of visual word recognition in the left and right cerebral hemispheres have attempted to control for confounding differences in the retinal placement (and hence visual acuity) of the beginnings of words by re-orientating normally-horizontal words vertically. However, despite the popularity of this approach, little is known about the precise effects that vertically orientating normally-horizontal words exert on hemispheric processes of word recognition. In this study, we investigated perception of horizontal and vertical English words and nonwords in the left visual field (LVF) and right visual field (RVF). An eye-tracking device ensured central fixation and a 2AFC paradigm (Reicher-Wheeler task) suppressed influences of non-perceptual bias. Horizontal stimuli produced a strong right visual field advantage for words but not for nonwords, whereas, vertical stimuli produced no hemifield differences at all. Moreover, vertical stimuli produced an advantage for words over nonwords in both visual fields whereas horizontal stimuli produced this effect only in the right visual field. Implications of these findings for the sensitivity of processes of word perception to stimulus orientation in the two cerebral hemispheres are discussed.     

Verbal visual extinction in right/left hemisphere lesion patients and the problem of lexical access

In order to explore perceptual processes preceding visual lexical access, we compared single words reading in both visual hemifields in right or left hemisphere damaged patients. Words were tachistoscopically presented in three conditions: (1) one word in one visual hemifield, (2) two words, one in each visual hemifield aside the fovea, (3) one longer word in both visual hemifields, centred on the fovea. In many patients, suffering from right as well as left hemisphere lesions, reading remains normal for unilateral presentation whereas bilateral presentation induced extinction in the hemifield contralateral to the lesion. Nevertheless, extinction was not frequently observed for the right or the left part of long centred words. Extinction proved to be most frequent in lesions centred on the occipito-temporo-parietal area. In addition, we found visual extinction not to be related to auditory extinction in verbal dichotic listening.     

Visual field effects and short-term memory for verbal material

The role of memory in the usual right visual field superiority for verbal material reported with normal subjects was investigated. Nonsense words were presented vertically in either the left or right visual field. The exposure duration, which was individually determined for each subject to produce about 75% correct responses, ranged from 5 to 25 msec. After a delay of 0, 5, or 10 sec the subject decided whether or not a nonsense word exposed in central vision was the same as the stimulus word.With males, the results suggested that the right visual field superiority represents left hemisphere specialization for retention of verbal material and hemispheric equality in reception. With females no visual field superiority was found perhaps indicating that both hemispheres receive and retain verbal information equally well. The findings support the concept of less-complete lateralization of linguistic and spatial functions in females.     

Interhemispheric cooperation and activation in integration of verbal information

Subjects had to judge the semantic relation between two tachistoscopically presented German adjectives. In Exp. I, the two words were projected simultaneously, either both to the left visual field (i.e. to the right hemisphere, LVF-RH), or both to the right visual field (i.e. to the left hemisphere, RVF-LH), or one word to each visual field (i.e. to both hemispheres, EVF-BH). The results yielded a significantly higher performance in the condition EVF-BH than in the two unilateral conditions, without a significant difference between the latter two conditions. In Exp. II, the two words were shown successively. With bilateral presentation, a distinction was made as to whether the left visual field (EVF-BH-L) or the right visual field (EVF-BH-R) was stimulated first. The significantly highest performance was shown in conditions RVF-LH and EVF-BH-R compared with the condition EVF-BH-L, and the significantly poorest performance in the condition LVF-RH compared with the condition EVF-BH-L. The results provide evidence for (1) an intrahemispheric interference with simultaneous unilateral presentation, (2) a cooperative interhemispheric interaction with simultaneous bilateral presentation, and (3) an interhemispheric priming effect with successive bilateral presentation when the left hemisphere was stimulated first.     

Comparison between visual half-field performance and cerebral blood flow changes as indicators of language dominance

The determination of hemispheric language dominance (HLD) can be accomplished in two ways. One approach relies on hemispheric differences in cerebral blood flow velocity (CBFV) changes during language activity, while the other approach makes use of performance differences between the left and right visual field when verbal stimuli are presented in a tachistoscopic visual field paradigm. Since both methodologically different approaches claim to assess functional HLD, it seems plausible to expect that the respective laterality indices (LI) would correspond. To test this expectation we measured language lateralisation in 58 healthy right-handed, left-handed, and ambidextrous subjects with both approaches. CBFV changes were recorded with functional transcranial Doppler sonography (fTCD). We applied a lexical decision task with bilateral visual field presentation of abstract nouns and, in addition, a task of mental word generation. In the lexical decision task, a highly significant right visual field advantage was observed for number of correct responses and reaction times, while at the same time and contrary to expectation the increase of CBFV was significantly higher in the right than left hemisphere. During mental word generation, the acceleration of CBF was significantly higher in the left hemisphere. A comparison between individual LI derived from CBF measurement during mental word generation and from visual field performances in the lexical decision task showed a moderate correspondence in classifying the subjects' HLD. However, the correlation between the corresponding individual LI was surprisingly low and not significant. The results are discussed with regard to the issue of a limited reliability of behavioural LI on the one hand and the possibility of a fundamental difference between the behavioural and the physiological indicators of laterality on the other hand.     

Comparison between visual half-field performance and cerebral blood flow changes as indicators of language dominance

The determination of hemispheric language dominance (HLD) can be accomplished in two ways. One approach relies on hemispheric differences in cerebral blood flow velocity (CBFV) changes during language activity, while the other approach makes use of performance differences between the left and right visual field when verbal stimuli are presented in a tachistoscopic visual field paradigm. Since both methodologically different approaches claim to assess functional HLD, it seems plausible to expect that the respective laterality indices (LI) would correspond. To test this expectation we measured language lateralisation in 58 healthy right-handed, left-handed, and ambidextrous subjects with both approaches. CBFV changes were recorded with functional transcranial Doppler sonography (fTCD). We applied a lexical decision task with bilateral visual field presentation of abstract nouns and, in addition, a task of mental word generation. In the lexical decision task, a highly significant right visual field advantage was observed for number of correct responses and reaction times, while at the same time and contrary to expectation the increase of CBFV was significantly higher in the right than left hemisphere. During mental word generation, the acceleration of CBF was significantly higher in the left hemisphere. A comparison between individual LI derived from CBF measurement during mental word generation and from visual field performances in the lexical decision task showed a moderate correspondence in classifying the subjects' HLD. However, the correlation between the corresponding individual LI was surprisingly low and not significant. The results are discussed with regard to the issue of a limited reliability of behavioural LI on the one hand and the possibility of a fundamental difference between the behavioural and the physiological indicators of laterality on the other hand.     

Hemisphere lateralization is influenced by bilingual status and composition of words

It has been generally accepted that the left hemisphere is more functionally specialized for language than the right hemisphere for right-handed monolinguals. But more and more studies have also demonstrated right hemisphere advantage for some language tasks with certain participants. A recent comprehensive survey has shown that hemisphere lateralization of language depends on the bilingual status of the participants, with bilateral hemispheric involvement for both languages of early bilinguals, who acquired both languages by age of 6, left hemisphere dominance for language of monolinguals, and also left hemisphere dominance for both languages of late bilinguals, who acquired the second language after age of 6. We propose a preliminary model which takes into account both composition of stimulus words and bilingual status of participants to resolve the apparent controversies regarding hemisphere lateralization of various reading experiments in the literature with focus on Chinese characters, and to predict lateralization patterns for future experiments in Chinese word reading. The bilingual status includes early bilingual, late bilingual and monolingual. However, we have tested this model only with late Chinese-English bilingual participants by using a Stroop paradigm in this paper, though the aim of our model is to disentangle the controversies in the lateralization effect of Chinese character reading. We show here with stimuli written in Chinese single characters that the Stroop effect was stronger when the stimuli were presented to the right than to the left visual field, implying that the language information and color identification/naming may interact more strongly in the left hemisphere. Therefore, our experimental results indicate left hemisphere dominance for Chinese character processing, providing evidence for one part of our model.     

Manipulating hemispheric attentional mechanisms to modulate word retrieval in aphasia

Background: Emerging evidence suggests that left hemisphere damage may create an attentional bias towards stimuli initially processed in the right hemisphere.

Aims: The current study aimed to investigate whether this hemispheric attentional bias influences spoken word production in a picture–word interference task.

Methods & Procedures: Two participants with aphasia and seven healthy controls named centrally presented pictures that were preceded by a distractor word which appeared in either the left or right visual field 200 ms prior to the picture. Distractor words were semantically related, phonologically related, unrelated, or the name of the picture. Results were analysed in terms of response times and accuracy.

Outcomes & Results: A greater overall facilitation effect was found in the left visual field/right hemisphere condition for both participants with aphasia, however this varied depending on distractor condition. These results are consistent with an attentional bias towards linguistic stimuli initially presented to the right hemisphere. In contrast, the results of the control group suggest a reduction in the lateralisation of language processing to the left hemisphere in healthy ageing.

Conclusions: These results suggest that spoken word production may be influenced by changes in attentional mechanisms following left hemisphere damage in aphasia, as well as changes in hemispheric lateralisation and inhibition in healthy ageing. Identifying attentional conditions that optimise language performance in aphasia may have implications for new treatments in language rehabilitation.     

Visual Hemifield Asymmetry for Naming Concrete Nouns and Verbs in Children Between Seven and Eleven Years of Age

Three-letter concrete nouns (Experiment 1) or verbs (Experiment 2) were exposed tachistoscopically in the right and left visual hemifields using a technique of bilateral stimulation with cued order of report. For subjects aged seven to eleven years, both types of word gave a small RVF advantage on words reported first and a larger RVF advantage on words reported second. This interaction between order of report and visual hemifield has been found by Young, Bion and Ellis (1980) to characterize stimuli which the right hemisphere is able to recognize. The absence of age × visual hemifield interactions argues against any progressive lateralisation through childhood, but may be indicative of the way the right hemisphere acquires its reading vocabulary.     

Opposite brain laterality in analogous auditory and visual tests

Laterality for language processing can be assessed by auditory and visual tasks. Typically, a right ear/right visual half-field (VHF) advantage is observed, reflecting left-hemispheric lateralization for language. Historically, auditory tasks have shown more consistent and reliable results when compared to VHF tasks. While few studies have compared analogous tasks applied to both sensory modalities for the same participants, one such study by Voyer and Boudreau [(2003). Cross-modal correlation of auditory and visual language laterality tasks: a serendipitous finding. Brain Cogn, 53(2), 393–397] found opposite laterality for visual and auditory language tasks. We adapted an experimental paradigm based on a dichotic listening and VHF approach, and applied the combined language paradigm in two separate experiments, including fMRI in the second experiment to measure brain activation in addition to behavioural data. The first experiment showed a right-ear advantage for the auditory task, but a left half-field advantage for the visual task. The second experiment, confirmed the findings, with opposite laterality effects for the visual and auditory tasks. In conclusion, we replicate the finding by Voyer and Boudreau (2003) and support their interpretation that these visual and auditory language tasks measure different cognitive processes.     

Interhemispheric connectivity during lateralized lexical decision

The well‐established right visual field (RVF‐lh) advantage in word recognition is commonly attributed to the typical left hemisphere dominance in language; words presented to the LVF‐rh are processed less efficiently due to the need for transcallosal transfer from the right to left hemisphere. The exact stage for this hemispheric transfer is currently unsettled. Some studies suggest that transfer occurs at very early stages between primary visual regions, whereas other studies suggest that transfer occurs between the left visual word form area and its right hemisphere homolog. This study explores these conflicting accounts and finds evidence for both. Participants conducted a lateralized lexical decision task with both unilateral and bilateral display conditions. Connectivity analyses were conducted from magnetoencephalography signals that were localized to the left middle occipital gyrus (LMOG), right middle occipital gyrus (RMOG), left visual word form area (LVWFA), and right visual word form area (RVWA). Results from unilateral trials showed asymmetrical interhemispheric connectivity from the RMOG to LMOG and symmetrical interhemispheric connectivity between the LVWFA and RVWFA. Furthermore, bilateral presentations led to reduced interhemispheric connectivity between both homologous region of interest pairs. Together, these results suggest that lateralized word recognition involves multiple stages of interhemispheric interactions and that these interactions are reduced with bilateral displays.     

Hemifield effects of spatial attention in early human visual cortex

Early visual areas (V1, V2, V3/VP, V4v) contain representations of the contralateral hemifield within each hemisphere. Little is known about the role of the visual hemifields along the visuo-spatial attention processing hierarchy. It is hypothesized that attentional information processing is more efficient across the hemifields (known as bilateral field advantage) and that the integration of information is greater within one hemifield as compared with across the hemifields. Using functional magnetic resonance imaging we examined the effect of distance and hemifield on parallel attentional processing in the early visual areas (V1-V4v) at individually mapped retinotopic locations aligned adjacently or separately within or across the hemifields. We found that the bilateral field advantage in parallel attentional processing over separated attended locations can be assigned, at least partly, to differences in distractor position integration in early visual areas. These results provide evidence for a greater integration of locations between two attended locations within one hemifield than across both hemifields. This nicely correlates with behavioral findings of a bilateral field advantage in parallel attentional processing (when distractors in between cannot be excluded) and a unilateral field advantage if attention has to be shifted across separated locations (when locations in between were integrated).