Selective semantic-lexical impairment of language comprehension in right-brain-damaged patients

Transcranial Direct Current Stimulation Effects on the Neural Substrate of Conceptual Representations

The aim of this study was to shed light on the neural substrate of conceptual representations starting from the construct of higher-order convergence zones and trying to evaluate the unitary or non-unitary nature of this construct. We used the 'Thematic and Taxonomic Semantic (TTS) task' to investigate (a) the neural substrate of stimuli belonging to biological and artifact categories, (b) the format of stimuli presentation, i.e., verbal or pictorial, and (c) the relation between stimuli, i.e., categorial or contextual. We administered anodal transcranial direct current stimulation (tDCS) to different brain structures during the execution of the TTS task. Twenty healthy participants were enrolled and divided into two groups, one investigating the role of the anterior temporal lobes (ATL) and the other the temporo-parietal junctions (TPJ). Each participant underwent three sessions of stimulation to facilitate a control condition and to investigate the role of both hemispheres. Results showed that ATL stimulation influenced all conceptual representations in relation to the format of presentation (i.e., left-verbal and right-pictorial). Moreover, ATL stimulation modulated living categories and taxonomic relations specifically, whereas TPJ stimulation did not influence semantic task performances.

Brain hemispheres with right temporal lobe damage swap dominance in early auditory processing of lexical tones

Labor division of the two brain hemispheres refers to the dominant processing of input information on one side of the brain. At an early stage, or a preattentive stage, the right brain hemisphere is shown to dominate the auditory processing of tones, including lexical tones. However, little is known about the influence of brain damage on the labor division of the brain hemispheres for the auditory processing of linguistic tones. Here, we demonstrate swapped dominance of brain hemispheres at the preattentive stage of auditory processing of Chinese lexical tones after a stroke in the right temporal lobe (RTL). In this study, we frequently presented lexical tones to a group of patients with a stroke in the RTL and infrequently varied the tones to create an auditory contrast. The contrast evoked a mismatch negativity response, which indexes auditory processing at the preattentive stage. In the participants with a stroke in the RTL, the mismatch negativity response was lateralized to the left side, in contrast to the right lateralization pattern in the control participants. The swapped dominance of brain hemispheres indicates that the RTL is a core area for early-stage auditory tonal processing. Our study indicates the necessity of rehabilitating tonal processing functions for tonal language speakers who suffer an RTL injury.

The Effect of Right Temporal Lobe Gliomas on Left and Right Hemisphere Neural Processing During Speech Perception and Production Tasks

Using fMRI, we investigated how right temporal lobe gliomas affecting the posterior superior temporal sulcus alter neural processing observed during speech perception and production tasks. Behavioural language testing showed that three pre-operative neurosurgical patients with grade 2, grade 3 or grade 4 tumours had the same pattern of mild language impairment in the domains of object naming and written word comprehension. When matching heard words for semantic relatedness (a speech perception task), these patients showed under-activation in the tumour infiltrated right superior temporal lobe compared to 61 neurotypical participants and 16 patients with tumours that preserved the right postero-superior temporal lobe, with enhanced activation within the (tumour-free) contralateral left superior temporal lobe. In contrast, when correctly naming objects (a speech production task), the patients with right postero-superior temporal lobe tumours showed higher activation than both control groups in the same right postero-superior temporal lobe region that was under-activated during auditory semantic matching. The task dependent pattern of under-activation during the auditory speech task and over-activation during object naming was also observed in eight stroke patients with right hemisphere infarcts that affected the right postero-superior temporal lobe compared to eight stroke patients with right hemisphere infarcts that spared it. These task-specific and site-specific cross-pathology effects highlight the importance of the right temporal lobe for language processing and motivate further study of how right temporal lobe tumours affect language performance and neural reorganisation. These findings may have important implications for surgical management of these patients, as knowledge of the regions showing functional reorganisation may help to avoid their inadvertent damage during neurosurgery.

Visual-to-auditory sensory substitution alters language asymmetry in both sighted novices and experienced visually impaired users

Visual-to-auditory sensory substitution devices (SSDs) provide improved access to the visual environment for the visually impaired by converting images into auditory information. Research is lacking on the mechanisms involved in processing data that is perceived through one sensory modality, but directly associated with a source in a different sensory modality. This is important because SSDs that use auditory displays could involve binaural presentation requiring both ear canals, or monaural presentation requiring only one - but which ear would be ideal? SSDs may be similar to reading, as an image (printed word) is converted into sound (when read aloud). Reading, and language more generally, are typically lateralised to the left cerebral hemisphere. Yet, unlike symbolic written language, SSDs convert images to sound based on visuospatial properties, with the right cerebral hemisphere potentially having a role in processing such visuospatial data. Here we investigated whether there is a hemispheric bias in the processing of visual-to-auditory sensory substitution information and whether that varies as a function of experience and visual ability. We assessed the lateralization of auditory processing with two tests: a standard dichotic listening test and a novel dichotic listening test created using the auditory information produced by an SSD, The vOICe. Participants were tested either in the lab or online with the same stimuli. We did not find a hemispheric bias in the processing of visual-to-auditory information in visually impaired, experienced vOICe users. Further, we did not find any difference between visually impaired, experienced vOICe users and sighted novices in the hemispheric lateralization of visual-to-auditory information processing. Although standard dichotic listening is lateralised to the left hemisphere, the auditory processing of images in SSDs is bilateral, possibly due to the increased influence of right hemisphere processing. Auditory SSDs might therefore be equally effective with presentation to either ear if a monaural, rather than binaural, presentation were necessary.

Representional and connectivity-based accounts of the cognitive consequences of atrophy of the right and left anterior temporal lobes

According to the original "hub-and-spoke" model of conceptual representations, the neural network for semantic memory requires a single convergence zone located in the anterior temporal lobes (ATLs). However, a more recent version of this model acknowledges that a graded specialization of the left and right ATLs might emerge as a consequence of their differential connectivity with language and sensory-motor regions. A recent influential paper maintained that both the format of semantic representations (representational account) and their differential connectivity (connectivity account) could contribute to the cognitive consequences of atrophy to the left versus the right ATL atrophy. That paper, however, also raised questions as to whether the distinction between representational and connectivity accounts is a meaningful question. I argue that an important theoretical difference exists between the representational and the connectivity-based models and that investigations, based on this difference, should allow to choose between these alternative accounts.

Lower- and higher-level models of right hemisphere language. A selective survey

The models advanced to explain right hemisphere (RH) language function can be divided into two main types. According to the older (lower-level) models, RH language reflects the ontogenesis of conceptual and semantic-lexical development; the more recent models, on the other hand, suggest that the RH plays an important role in the use of higher-level language functions, such as metaphors, to convey complex, abstract concepts. The hypothesis that the RH may be preferentially involved in processing the semantic-lexical components of language was advanced by Zaidel in splitbrain patients and his model was confirmed by neuropsychological investigations, proving that right brain-damaged patients show selective semanticlexical disorders. The possible links between lower and higher levels of RH language are discussed, as is the hypothesis that the RH may have privileged access to the figurative aspects of novel metaphorical expressions, whereas conventionalization of metaphorical meaning could be a bilaterally-mediated process involving abstract semantic-lexical codes.

Modulation of the inter-hemispheric processing of semantic information during normal aging. A divided visual field experiment

We evaluated the effect of normal aging on the inter-hemispheric processing of semantic information by using the divided visual field (DVF) method, with words and pictures. Two main theoretical models have been considered, (a) the HAROLD model which posits that aging is associated with supplementary recruitment of the right hemisphere (RH) and decreased hemispheric specialization, and (b) the RH decline theory, which assumes that the RH becomes less efficient with aging, associated with increased LH specialization. Two groups of subjects were examined, a Young Group (YG) and an Old Group (OG), while participants performed a semantic categorization task (living vs. non-living) in words and pictures. The DVF was realized in two steps: (a) unilateral DVF presentation with stimuli presented separately in each visual field, left or right, allowing for their initial processing by only one hemisphere, right or left, respectively; (b) bilateral DVF presentation (BVF) with stimuli presented simultaneously in both visual fields, followed by their processing by both hemispheres. These two types of presentation permitted the evaluation of two main characteristics of the inter-hemispheric processing of information, the hemispheric specialization (HS) and the inter-hemispheric cooperation (IHC). Moreover, the BVF allowed determining the driver-hemisphere for processing information presented in BVF. Results obtained in OG indicated that: (a) semantic categorization was performed as accurately as YG, even if more slowly, (b) a non-semantic RH decline was observed, and (c) the LH controls the semantic processing during the BVF, suggesting an increased role of the LH in aging. However, despite the stronger involvement of the LH in OG, the RH is not completely devoid of semantic abilities. As discussed in the paper, neither the HAROLD nor the RH decline does fully explain this pattern of results. We rather suggest that the effect of aging on the hemispheric specialization and inter-hemispheric cooperation during semantic processing is explained not by only one model, but by an interaction between several complementary mechanisms and models.

Why are the right and left hemisphere conceptual representations different?

The present survey develops a previous position paper, in which I suggested that the multimodal semantic impairment observed in advanced stages of semantic dementia is due to the joint disruption of pictorial and verbal representations, subtended by the right and left anterior temporal lobes, rather than to the loss of a unitary, amodal semantic system. The main goals of the present review are (a) to survey a larger set of data, in order to confirm the differences in conceptual representations at the level of the right and left hemispheres, (b) to examine if language-mediated information plays a greater role in left hemisphere semantic knowledge than sensory-motor information in right hemisphere conceptual knowledge, and (c) to discuss the models that could explain both the differences in conceptual representations at the hemispheric level and the prevalence of the left hemisphere language-mediated semantic knowledge over the right hemisphere perceptually based conceptual representations.

The contribution of language to the right-hemisphere conceptual representations: a selective survey

Although levels of verbal and pictorial performance are known to depend on the degree of left versus right atrophy in the early stages of semantic dementia, the nature of these differences remains controversial. It has been proposed that there is a unitary, bilaterally represented, abstract semantic system and that differential task performance reflects the impact of greater connectivity between the left anterior temporal lobe (ATL) and the left dominant language systems. This interpretation explains the greater involvement of the left ATL in verbally coded semantic knowledge, but not the prevalence of the right hemisphere in pictorial representations. An alternative account is provided by the sensory-motor model of conceptual knowledge, which assumes that each conceptual representation results from the convergence of different perceptual, motor, and verbally coded sources of knowledge in a given brain area. According to this model, the weight of verbal information should prevail in left ATL conceptual representations, because of the dominance of the left hemisphere for language, whereas the weight of sensory-motor sources of knowledge should be greater in the right ATL representations, because the right hemisphere plays a greater role in processing sensory-motor information. If the difference between right and left conceptual representations is quantitative and due to the different weight of sensory-motor and verbal sources of knowledge in their composition, we should observe an elementary, but selective representation of semantic-lexical knowledge in the intact right hemisphere and a mild but selective semantic-lexical impairment in right-brain-damaged patients. Results of the present survey support this hypothesis.

The role of commonality, distinctiveness and importance of semantic features in persons with aphasia

OBJECTIVE

Semantic feature approaches are frequently included in treatment for people with aphasia. The present study investigated the role of distinctiveness and importance in the semantic feature knowledge of people with aphasia. The relationships between feature knowledge and the ability to choose among semantically-related foils, comprehension and naming abilities were examined.

METHODS

Participants distinguished target nouns from related foils and completed a sorting task involving mid-importance common (MIC), mid-importance distinctive (MID), low-importance common (LIC) and low-importance distinctive (LID) features. Participants also completed sub-tests from the short version of the Boston Diagnostic Aphasia Examination-Third Edition (BDAE-3) and Boston Naming Test-Second Edition (BNT-2). Participants were divided into two groups based on ability to accurately select target nouns from semantically-related foils.

RESULTS

Group 1, participants with intact ability to choose among related foils, was significantly less impaired with the identification of distinctive features than Group 2, those with difficulty choosing among related foils. Importance was not a significant factor when comparing mid-importance to low-importance features.

CONCLUSIONS

These results suggest that distinctive feature knowledge contributes in a significant way to the integrity of semantic representations in people with aphasia which can influence their performance of language tasks.

The dynamic nature of language lateralization: effects of lexical and prosodic factors

In dichotic listening, a right ear advantage for linguistic tasks reflects left hemisphere specialization, and a left ear advantage for prosodic tasks reflects right hemisphere specialization. Three experiments used a response hand manipulation with a dichotic listening task to distinguish between direct access (relative specialization) and callosal relay (absolute specialization) explanations of perceptual asymmetries for linguistic and prosodic processing. Experiment 1 found evidence for direct access in linguistic processing and callosal relay in prosodic processing. Direct access for linguistic processing was found to depend on lexical status (Experiment 2) and affective prosody (Experiment 3). Results are interpreted in terms of a dynamic model of hemispheric specialization in which right hemisphere contributions to linguistic processing emerge when stimuli are words, and when they are spoken with affective prosody.

Performance and reaction times in monaural localization of first names in the horizontal plane

Many studies have been conducted to measure monaural azimuthal sound localization performance with different sounds varying in frequency and complexity, but few have used linguistic stimuli. The present experimental design used subjects' first names in a monaural azimuthal localization task. Analysis of response accuracy showed that subjects are not more accurate in localizing their own first name than in localizing other first names and that there was no significant advantage of one ear over another. Reaction times were shorter when the subjects localized their own first name than when they localized any other first names and there was no significant ear advantage, but localizing other first names took more time with the right than with the left ear. All stimuli were better and more quickly localized on the side of the open ear, and there was no difference in acuity or velocity of localization with the two different speaker voices used. These results suggest that first names are processed through the controlateral auditory pathway and can be analyzed in the right hemisphere.

Age-related evolution of the contribution of the right hemisphere to language: absence of evidence

The age difference observed between Wernicke's and Broca's aphasics has been understood by some authors as an indication of a progressive diminution of the contribution of the right hemisphere to language throughout the life span. To test this hypothesis, 24 right-hemisphere-damaged (RHD) and 24 normal control adults were submitted to six tasks looking at different aspects of language abilities. Results showed that RHDs performed less well than normal subjects on 3 of these tasks, but that this difference was not linked with age (younger than 55 versus older than 65 years). Consequently, these results do not support models of functional brain organization suggesting a decreasing contribution of the right hemisphere to language abilities with age.

The use of contextual information by right brain-damaged individuals in the resolution of ambiguous pronouns

Two experiments were conducted with the primary purpose of investigating the ability of right brain-damaged (RBD) individuals to use contextual information--at the level of the single sentence, in terms of the integration of information between clauses, and at the level of a minimal discourse (i.e., two sentences)--in the resolution of ambiguous pronouns. The investigation was extended to a group of left brain-damaged (LBD) and non-brain-damaged (NBD) individuals. Contrary to the prevailing view that RBD patients have difficulty in the use of contextual information to process language, both experiments were consistent in demonstrating that the RBD group was influenced by contextual information in a manner similar to that demonstrated by both the LBD and NBD groups.

The use of contextual information related to general world knowledge by right brain-damaged individuals in pronoun resolution

This study investigated the ability of right brain-damaged individuals (RBD) to use contextual information to resolve ambiguous pronouns. Subjects were presented with sentence pairs and required to resolve the ambiguous pronoun in the second sentence. Contrary to the prevailing view that RBD patients have difficulty using contextual information to integrate language, the RBD group demonstrated a normal pattern of response, demonstrating a sensitivity to the pragmatic information contained in the leading sentence. They responded more quickly to sentences with a pragmatically constrained preferred referent than to those sentences for which there was no preferred referent. As well, they chose the preferred referent significantly more often than the non-preferred referent. These results suggest that RBD patients can use contextual information at the level of a minimal discourse (i.e., two sentences).

Hemispheric specialization for word classes with visual presentations and lexical decision task

In the present paper we study the possible RH capabilities for the processing of adjectives and verbs of high frequency and medium imagery using a lexical decision task and a horizontal display. In the analysis of both RTs and mean errors, a RVF advantage is obtained. The interaction VF x Word Class did not reach significance. Therefore, we did not find evidence of differences in the visual-field effect for any syntactic class. These results support a LH superiority for the processing of both adjectives and verbs. For the nonword conditions (pseudoverbs and pseudoadjectives), no visual field differences were observed in either group. Methodological aspects are also discussed.

Right hemisphere specialization for the identification of emotional words and sentences: evidence from stroke patients

This study examines the contribution of the lexical/verbal channel to emotional processing in 16 right brain-damaged (RBD), 16 left brain-damaged (LBD) and 16 normal control (NC) right-handed adults. Emotional lexical perception tasks were developed; analogous nonemotional tasks were created to control for cognitive and linguistic factors. The three subject groups were matched for gender, age and education. The brain-damaged groups were similar with respect to cerebrovascular etiology, months post-onset, sensory-motor status and lesion location. Parallel emotional and nonemotional tasks included word identification, sentence identification and word discrimination. For both word tasks, RBDs were significantly more impaired than LBDs and NCs in the emotional condition. For all three tasks, RBDs showed a significantly greater performance discrepancy between emotional and nonemotional conditions than did LBDs or NCs. Results were not affected by the valence (i.e. positive/negative) of the stimuli. These findings suggest a dominant role for the right hemisphere in the perception of lexically-based emotional stimuli.

A preliminary characterization of lexical emotional expression in right and left brain-damaged patients

Disorders in nonverbal communication of emotion have been documented in patients with right hemisphere pathology; lexical expression of emotion is virtually unstudied. In this preliminary investigation, emotionally laden slides were used to elicit discourse from right brain-damaged (RBD), left brain-damaged (LBD), and normal control (NC) subjects. New techniques were developed to examine the ability of these subjects to express emotion in words; formalistic and pragmatic analyses of the discourse were conducted. RBDs, relative to NCs and LBDs, were less successful in using words to convey emotion and produced words of lower emotional intensity. LBD aphasics, despite their linguistic deficits, were comparable to NCs in conveying emotional valence. The data tend to support the speculation that the right hemisphere is dominant for lexical expression of emotion. This study has implications for the neuropsychological investigation of language, emotion, and the brain.

Depression, episodic behavioral dyscontrol, and polydipsia following right temporal lobe damage

A patient referred to the authors for evaluation and treatment of depression, behavioral dyscontrol syndrome, and polydipsia is described. The authors reviewed his medical status and, finding damage to his right temporal lobe, conceptualized his symptom constellation as representing interictal syndrome and treated him with carbamazepine. His affective symptoms, but not the polydipsia, improved following treatment with carbamazepine.

Semantic capabilities of the left and right cerebral hemispheres in categorization tasks: effects of verbal-pictorial presentation

Two lateral tachistoscopic experiments were carried out to test semantic capabilities of the left and right cerebral hemispheres through categorization tasks with verbal and pictorial presentations. RVF advantages were obtained for verbal presentations in both category-membership and category-matching tasks. However, no significant visual-field differences were found for any pictorial presentation. We also found a higher degree of sensitiveness of the positive judgements for the detection of hemispheric differences and sex differences in patterns of functional asymmetries with a greater lateralization in males.

The influence of semantic and perceptual factors on lexical comprehension in aphasic and right brain-damaged patients

We investigated whether the errors made by aphasic patients and right brain-damaged (RBD) patients on a word-picture matching test were differently related to the semantic and perceptual difficulties of the task. To this effect, the target picture was presented in one condition along with two semantically similar distractors, in another condition with two perceptually similar distractors, and in a third condition with two distractors that were both semantically and perceptually similar. There were also two control conditions in which part of targets that had been originally shown with semantic distractors were now presented with perceptual distractors and vice versa. The findings were consistent with the hypothesis that aphasics mainly fail when the task involves semantic discrimination and RBD patients when it involves perceptual discrimination. In aphasics the semantic perceptual condition produced the highest number of errors, but this was due, it was argued, to an increase of the semantic demands of the task.

The cerebral localization of neuropsychological impairment in Alzheimer's disease: a SPECT study

Twenty-three patients with a clinical diagnosis of Alzheimer's disease were examined with a set of neuropsychological tests and with 99mTc-hexamethyl-propyleneamineoxime (HMPAO) single photon emission computed tomography (SPECT). Correlations between test results and indices of regional HMPAO distribution were analysed by multidimensional scaling (MDS). Test results covaried positively with relative HMPAO uptake of frontal, inferior parietal and superior temporal regions but not, or in a negative way, with the remainder of the regions. When only positive correlations were analysed, MDS suggested two dimensions of organization: one was related to a dichotomy between frontal and temporo-parietal regions. The relationship of test results to this dimension was largely consistent with common neuropsychological knowledge. A second, less stringent dimension of organization opposed right and left hemisphere regions. The ordering of test results with respect to this dimension was only partly consistent with what is known about the lateralization of neuropsychological deficits from the study of localized brain lesions. The possibility is considered that these inconsistencies may reflect the effect of disproportionally severe involvement of extended cortical systems which modulates the sequels of localized brain damage.

Electrical stimulation of the human hippocampus produces verbal intrusions during memory testing

Verbal memory testing was conducted during electrical stimulation of the human hippocampus in 12 epilepsy surgery candidates with unilateral temporal lobe seizure onset. Performance was assessed during baseline, left hippocampal stimulation and right hippocampal stimulation. Verbal intrusion errors were greater during electrical stimulation of the hippocampus contralateral to the seizure focus. These findings suggest that verbal intrusions are related to memory deficits, and that patients with cerebral disease who intrude words from an earlier portion of a learning test are likely to have bilateral cerebral dysfunction.

Vocal reaction times to unilaterally presented concrete and abstract words: towards a theory of differential right hemispheric semantic processing

Previous studies investigating hemispheric organization for processing concrete and abstract nouns have provided conflicting results. Using manual reaction time tasks some studies have shown that the right hemisphere is capable of analyzing concrete words but not abstract. Others, however, have inferred that the left hemisphere is the sole analyzer of both types of lexicon. The present study tested these issues further by measuring vocal reaction times of normal subjects to unilaterally presented concrete and abstract items. Results were consistent with a model of functional localization which suggests that the minor hemisphere is capable of differentially processing both types of lexicon in the presence of a dominant left hemisphere.

Qualitatively different organizational structures of lexical knowledge in the left and right hemisphere

The present study investigates and discusses the organization of lexical knowledge in the intact left and right hemisphere within the framework of hemisphere-specific cognitive modes of processing. Using a divided visual field technique, word pairs of concrete nouns had to be judged. Semantic relation was either intraconceptual (coordinates) or interconceptual (locative). The results suggest that the left hemisphere, lexical structures are predominantly based on intraconceptual relationships corresponding to its analytic sequential processing mechanism, whereas in the right hemisphere, lexical entries are exclusively associated by means of interconceptual relationships in accordance with its "gestalthaft" holistic processor.

Stimulus categorization by brain-damaged patients

Patients with localized insult to the right hemisphere, or to either the anterior or the posterior portion of the left hemisphere, as well as neurologically intact controls, evaluated stimuli on a seven-point rating scale for their degree of category membership. The stimuli were taken from one of two continua, one composed of fruit and vegetable items, and the other of items differing in hue and shape. Different subsets of stimuli provided different contexts for the judgments of category membership. The two left-hemisphere groups showed anomalies in categorizing the fruit and vegetable items but not the perceptual items, while the reverse was true for the right-hemisphere patients. Moreover, both left-hemisphere groups demonstrated context effects in their judgments of the representativeness of the fruit and vegetable items, but differed in the way in which they responded to changing contexts. Left posterior patients demonstrated weak category boundaries and even reclassified items. In contrast, patients with left anterior damage showed highly categorical responses and less differentiation of items within a category. All groups showed striking context effects in judgments of perceptual items in terms of changes in representativeness ratings and the location of a category boundary. Alternative interpretations of the results are offered.

Verbal memory and semantic clustering in right brain-damaged patients

Twenty-four right brain-damaged patients without ostensive signs of intellectual impairment or disturbances of verbal comprehension, and 20 normal control subjects were given two lists of words, one (the Rey's Auditory) in which 15 words were semantically unrelated and a second in which 15 two-syllable words belonged to one of three categories. The results demonstrated no difference between the two subject groups, either in the immediate or the delayed recall sections of the Rey's test. The immediate recall section of the semantic verbal memory task, on the contrary, showed significantly poor performance by the right brain-damaged patients. These results suggest an impairment of semantic clustering processes after right hemisphere damage.

Lexical judgments after right- or left-hemisphere injury

Patients with unilateral left- or right-hemisphere lesions were asked to make similarity judgments to visually presented words on the basis of rhyme, meaning or visual similarity. The left-hemisphere-injured group was significantly impaired, relative to controls, for all types of lexical judgments, with the greatest impairment in the rhyme condition. Patients with right-hemisphere injury were also impaired, but only when lexical judgments were based on meaning. The results are generally consistent with normal and split-brain lateralization findings, and provide evidence supportive of a right-hemisphere contribution to some aspects of lexical semantic processing.

Dichotic listening tests in studying brain-behavior relationships

The magnitude of perceptual asymmetry (PA) on a CVC fused dichotic words test and on VCV and CV fused nonsense syllables tests were compared. In each test the set of distinguishing phonemic cues was the same; the six English stop consonants, b,p,d,t,g,k. Although test-retest reliability was very high on all three tests there was no correlation across individuals between the degrees of PA on different tests. Moreover, the magnitude of PA on the VCV nonsense test increased as field dependence (FD) increased on the field dependence index (FDI) of the WAIS while there was no relationship between FD and the magnitude of PA on the CVC words test. In addition, concurrent visual tasks increased PA on the VCV nonsense test and decreased it on the words test. In order to facilitate the use of such data, Kimura's classical model of the physiological basis of PA is modified by including components of primary receptive and secondary and tertiary associative function. Comparison of highly similar PA measures, that differ in specific ways, is discussed as a means of collecting data for mapping cerebral functional space and exploring brain-behavior relationships.

Language in right-handers with right-hemisphere lesions: a preliminary study including anatomical, genetic, and social factors

A comprehensive test battery was devised to study the effects of right hemisphere lesions on the speech and language of "nonaphasic" dextrals. Data were thus obtained for 62 subjects, 20 of them neurologically healthy and 42 with a focal right hemisphere lesion resulting from a cerebro-vascular accident. A preliminary global analysis of these data is reported. Anomalies were observed in 33 brain-damaged subjects. Although discreet in all cases, these anomalies were shown to have various degrees of severity. Given the population submitted to this study, the subject most likely to show such anomalies was defined, genetically, as a right-handed adult with a family history of ambidextrality or left-handedness and, socially, as one with a relatively limited education. The implications of these findings are discussed together with the problem of the anatomo-clinical correlations of language disorders resulting from right hemisphere lesions in "nonaphasic" dextrals.

Right-hemisphere linguistic functioning

This review examined the linguistic processing abilities and potential of adults' nondominant hemisphere. Relevant literature was reviewed for experimental evidence of qualitative and quantitative differences in language functioning between the left and right cerebral hemispheres. Selected studies representing typical methodologies and subjects were included.

Braille reading and left and right hemispace

Twelve blind adults were timed in locating phonologically and semantically defined targets in Braille lists. The "reading" hand was placed either out from or across the body, i.e. in ipsilateral or contralateral hemispace. Despite strong and consistent, if idiosyncratic, hand superiorities for all types of list, contrary to two previous reports there was no evidence of either a general left-hand preference or an overall left-hand superiority. Moreover neither the magnitude nor the direction of hand superiorities changed when hands were tested in contralateral hemispace. At least this complex continuous task, hemisphere-hand connections appear more important than hemisphere-hemispace relationships. Left-hand (or left-hemispace) superiorities in tactual tasks of a verbal nature may only occur with novel, unfamiliar or perceptually degraded materials.