Hemisphere differences in conscious and unconscious word reading

Hemisphere differences in word reading were examined using explicit and implicit processing measures. In an inclusion task, which indexes both conscious (explicit) and unconscious (implicit) word reading processes, participants were briefly presented with a word in either the right or the left visual field and were asked to use this word to complete a three-letter word stem. In an exclusion task, which estimates unconscious word reading, participants completed the word stem with any word other than the prime word. Experiment 1 showed that words presented to either visual field were processed in very similar ways in both tasks, with the exception that words in the right visual field (left hemisphere) were more readily accessible for conscious report. Experiment 2 indicated that unconsciously processed words are shared between the hemispheres, as similar results were obtained when either the same or the opposite visual field received the word stem. Experiment 3 demonstrated that this sharing between hemispheres is cortically mediated by testing a split-brain patient. These results suggest that the left hemisphere advantage for word reading holds only for explicit measures; unconscious word reading is much more balanced between the hemispheres.     

Impaired word naming in right-brain-damaged right-handers: error types and time-course analyses

The purpose of this study is to search for cues that could account for the fact that right-hemisphere lesions affect word naming when the criterion for naming is semantic. The authors analyzed the errors as well as the time course of productions of 35 vascular right-brain-damaged subjects (RBD) and 20 control subjects (C) in a semantic-based word-naming task. Results show that there are no differences between groups in terms of (a) the number of errors produced and, (b) the patterns of error types. However, results also show a reduction of verbal fluency for semantic criteria in RBD-subjects present only after the first 30 seconds of production. These results indicate that reduction of word production in RBD-subjects is not the consequence of nonspecific factors such as perseveration or spontaneity, but reflects problems with the less automatized processes permitting exploration of semantic organization, either because scanning process are affected, or because the presence of a discreet semantic impairment prevents scanning from being as efficient. Given that efficient exploration of semantic knowledge is important for lexico-semantic functioning, the present results suggest that the right hemisphere contributes to some aspects of lexico-semantic processing necessary for language production.     

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.     

Access to perceptual and conceptual information in the left and right hemispheres.

It is assumed that there are hemispheric differences in the type of information available for the processing of word meanings, e.g., categorical or associative information. In the present experiment, we used a semantic priming paradigm to examine whether perceptual or conceptual properties of word meanings would be associated with the left or right hemisphere. The present experiment also examined time-course activation of these properties across the hemispheres, using short and long stimulus onset asynchronies. The results indicated that perceptual information is available only in the right hemisphere at an early rather than a late stage of target processing, while conceptual information is available in both hemispheres at both early and later stages of target processing. It is suggested that the imagery system in the right hemisphere may contribute to the perceptual priming observed in this hemisphere.     

Lateralization of lexical codes in auditory word recognition

Three experiments examined the lateralization of lexical codes in auditory word recognition. In Experiment 1 a word rhyming with a binaurally presented cue word was detected faster when the cue and target were spelled similarly than when they were spelled differently. This orthography effect was larger when the target was presented to the right ear than when it was presented to the left ear. Experiment 2 replicated the interaction between ear of presentation and orthography effect when the cue and target were spoken in different voices. In Experiment 3, subjects made lexical decisions to pairs of stimuli presented to the left or the right ear. Lexical decision times and the amount of facilitation which obtained when the target stimuli were semantically related words did not differ as a function of ear of presentation. The results suggest that the semantic, phonological, and orthographic codes for a word are represented in each hemisphere; however, orthographic and phonological representations are integrated only in the left hemisphere.     

No strong evidence for lateralisation of word reading and face recognition deficits following posterior brain injury

Face recognition and word reading are thought to be mediated by relatively independent cognitive systems lateralised to the right and left hemispheres, respectively. In this case, we should expect a higher incidence of face recognition problems in patients with right hemisphere injury and a higher incidence of reading problems in patients with left hemisphere injury. We tested this hypothesis in a group of 31 patients with unilateral right or left hemisphere infarcts in the territory of the posterior cerebral arteries. In most domains tested (e.g., visual attention, object recognition, visuo-construction, motion perception), we found that both patient groups performed significantly worse than a matched control group. In particular, we found a significant number of face recognition deficits in patients with left hemisphere injury and a significant number of patients with word reading deficits following right hemisphere injury. This suggests that face recognition and word reading may be mediated by more bilaterally distributed neural systems than is commonly assumed.     

Hemispheric specialization in reading and word recognition

Three experiments dealing with hemispheric specialization are presented. In Experiment 1, words and/or faces were presented tachistoscopically to the left or right of fixation. Words were more accurately identified in the right visual field and faces were more accurately identified in the left visual field. A forced choice error analysis for words indicated that errors made for word stimuli were most frequently visually similar words and this effect was particularly pronounced in the left visual field. Two additional experiments supported this finding. On the basis of the results, it was argued that word identification is a multistage process, with visual feature analysis carried out by the right hemisphere and identification and naming by the left hemisphere. In addition, Kinsbourne's attentional model of brain function was rejected in favor of an anatomical model which suggests that simultaneous processing of verbal and nonverbal information does not constrict the attention of either hemisphere.     

Exploring the contribution of the cerebral hemispheres to language comprehension deficits in adults with developmental language disorder

A divided visual field, priming paradigm was used to observe how adults who have a history of developmental language disorder (DLD) access lexically ambiguous words. The results show that sustained semantic access to subordinate word meanings (such as BANK-RIVER), which is seen in control subjects, is disrupted in the right cerebral hemisphere for this special population of readers. In the left hemisphere, only the most dominant meaning of the ambiguous word shows sustained priming in both controls and DLD participants. Therefore, for the DLD readers the subordinate meanings of words are not primed in either hemisphere and, thus, may not be available during online processing and integration of discourse. This right hemisphere lexical access deficit might contribute to the language comprehension difficulties exhibited by adult readers with a history of DLD.     

The effect of associative strength on priming in the cerebral hemispheres

Recent studies have suggested that semantic memory is more diffusely organized in the right hemisphere of the brain and that words directed to this hemisphere are more likely to activate meanings distantly related to the input. It is argued that this model of language processes predicts that variations in the associative strength of word pairs should give rise to different patterns of priming in each hemisphere. Specifically, the right hemisphere should exhibit relatively more facilitation than the left in response to weaker associative relationships, whereas the left hemisphere should exhibit relatively more facilitation than the right in the context of stronger relationships. This study varied the strength of the semantic association between prime and target in a divided visual field priming procedure. The results were unequivocal in demonstrating similar associative strength functions in each hemisphere, under conditions that encouraged either automatic or controlled processing. Visual field differences in absolute RTs to words and in magnitude of facilitation effects support the claim that the data collected in this study are veridical with respect to priming processes in the hemispheres. It is suggested that current models of hemispheric language processes require further refinement.     

The effects of methylphenidate on levels of processing and laterality in children with attention deficit disorder

Effects of stimulant medication (methylphenidate) on levels (feature, name, semantic) of word processing by the left and right hemisphere were assessed in 31 attention- deficit- disordered children. In a double-blind procedure, same- different decisions were made to tachistoscopically presented word pairs under medication and placebo. Analysis of manual response times failed to show any negative effects of medication. Feature decisions were faster than name decisions, which were faster than semantic decisions. Methylphenidate induced a right visual field advantage (left hemisphere) for the name decision, which was interpreted as a normalization effect. The results suggest that (1) methylphenidate may selectively improve the phonological level of word processing and (2) methylphenidate's favorable therapeutic effect is produced through inhibition of excessive right hemisphere activity in response to task demands that engage the left hemisphere.This research is based in part upon a doctoral thesis completed by the first author in the Department of Education, University of Toronto. The authors thank Dr. William Logan and Dr. Wendy Roberts of the Hospital for Sick Children for permitting testing of patients in the Child Development Clinic. This research was supported in part by a doctoral fellowship from the Social Sciences and Humanities Research Council to the first author.     

中文阅读的副中央凹-中央凹效应：词n的语义透明度对词n-1的影响

研究探讨中文阅读中的副中央凹-中央凹效应。副中央凹-中央凹效应是指副中央凹处词的特性对中央凹处词汇加工的影响。实验以27名大学生为被试,采用句子阅读材料,考察词n的语义透明度特性对词n-1（高频、低频）加工的影响。结果表明,词n的语义透明度的高低对词n-1（高频、低频）的加工没有影响,没有出现副中央凹-中央凹效应。实验结果支持E-Z读者模型的假设。     

Right hemisphere metaphor processing? Characterizing the lateralization of semantic processes

Previous laterality studies have implicated the right hemisphere in the processing of metaphors, however it is not clear if this result is due to metaphoricity per se or another aspect of semantic processing. Three divided visual field experiments varied metaphorical and literal sentence familiarity. We found a right hemisphere advantage for unfamiliar sentences containing distant semantic relationships, and a left hemisphere advantage for familiar sentences containing close semantic relationships, regardless of whether sentences were metaphorical or literal. This pattern of results is consistent with theories postulating predominantly left hemisphere processing of close semantic relationships and predominantly right hemisphere processing of distant semantic relationships.     

Right Hemisphere Activation during Indirect Semantic Priming: Evidence from Event-Related Potentials

Healthy subjects performed a lexical decision task in a semantic priming paradigm while event-related potentials (ERPs) were recorded from 64 channels. Semantic distance between prime and target was varied by including directly, indirectly, and nonrelated word pairs. At centro-parietal electrodes an N400 to nonrelated pairs was elicited bilaterally which was sensitive only to direct, but not to indirect semantic priming. These N400 priming effects were mirrored by the RT data. At inferior fronto-temporal sites directly related words showed ERP priming effects over both hemispheres. However, indirectly related words only elicited ERP priming effects over the right hemisphere. These results support the hypothesis that the right hemisphere semantic system is involved in processing of remote semantic information.     

音高模式加工的大脑偏侧化研究

作为一种超音段成分,音高在言语的理解和产生过程中承担着重要作用,这些作用主要包括:区别不同声调的词汇意义,区别陈述、疑问等不同的语调,标志话语的情绪色彩等。音段、语义和句法信息的加工具有左脑优势,但音高模式加工的单侧优势及其机制还存在很多争论,本文从音高模式加工的两个主要理论———功能假设和声音信号假设出发,对相关研究加以评述。     

An analysis of speech perception in word deafness

A patient with a rather pure word deafness showed extreme suppression of right ear signals under dichotic conditions, suggesting that speech signals were being processed in the right hemisphere. Systematic errors in the identification and discrimination of natural and synthetic stop consonants further indicated that speech sounds were not being processed in the normal manner. Auditory comprehension improved considerably however, when the range of speech stimuli was limited by contextual constraints. Possible implications for the mechanism of word deafness are discussed.     

语义距离半球效应的ERP研究

以通过视觉通路呈现的汉语双字词为实验材料,操纵启动词与目标词的语义距离。在词汇决定实验中记录ERP,发现：（1）除N300外,P240亦对语义距离敏感,它可能是一种与语义加工有关的新的ERP成分;（2）P240在头皮中央偏左的部位较早出现,但在头皮右侧波幅较大;（3）N300和P240都不存在语义距离的半球效应,该结果没有证实右脑更专擅远距离语义加工的假设,表明使用汉语与使用拼音文字的脑机制存在差异。     

Laterality differences for word identification in bilinguals

Twenty-three Spanish-English bilinguals were tachistoscopically presented with four-letter common nouns. They viewed 20 word pairs, first in their native language, then in the other, for 40 msec under simultaneous bilateral exposure. This paradigm has previously shown a strong right visual field and therefore left hemisphere superiority for words in a single language. The results show a word identification advantage in the right visual field. This indicates a left hemisphere advantage for processing of both languages, regardless of which was learned first. There are nevertheless wide individual differences in the number of bilinguals showing the expected asymmetry, as compared with monolinguals. There may be a trend, therefore, for less unilaterality of language function in bilinguals, although both languages are seen as being equally lateralized.     

Optic aphasia and the right hemisphere: a replication and extension.

Optic aphasia is a rare, visual modality-specific naming disorder. We describe a patient who developed this disorder subsequent to a left occipital lobe infarction. Like another case that we described previously, this patient performed normally on a variety of tasks assessing the recognition of objects he could not name. Additionally, although he never read aloud a single word, his performance on lexical decision and word comprehension tasks was far better than chance. We suggest that his performance was mediated by a right hemisphere semantic system.     

TIME COURSE OF ACTIVATING BRAIN AREAS IN GENERATING VERBAL ASSOCIATIONS

Abstract— Generating a use far a visual word in comparison with reading the word aloud activates frontal attention areas first (170 MS), a left lateral frontal area next (250 ms), and then a left temporoparietal (Wernicke's) area (650 ms). A brief period of practice reduces these activations. If subjects are asked to respond to a word from the same practiced list by giving a novel use, the original activations reappear and are joined by activity similar in location and time to Wernicke's activation but in the right hemisphere. These findings demonstrate the time course of activations of neuroanatomical areas in word processing and indicate a role for the right hemisphere when semantic processing is more difficult, such as in generating a less frequent association in the presence of a highly practiced one.     

The perception of stress and lateralization of prosody

Three separate dichotic listening tasks were run to determine ear superiority for stress identification. When subjects were asked to identify stress placement in real word minimal stress pairs (hótdog vs. hot dóg), they demonstrated a right ear superiority. When these tokens were filtered so that phonetic and semantic information was eliminated and only the stress pattern remained, a different group of subjects showed a left ear advantage. Finally, with nonsense word counterparts to word stress pairs (bótgog vs. bot góg) preserving phonetic information but lacking semantic content, no ear asymmetry was found. These results suggest that as the linguistic significance of the stimuli is reduced, thereby lessening the linguistic function of stress, there is a less dominant involvement of the left hemisphere in stress processing. Results are discussed in relation to a theory of a functional integration of prosodic and segmental speech components that is paralleled by a working partnership of left and right hemisphere.