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PubMed2006

Unlocking the nature of the phonological-deep dyslexia continuum: the keys to reading aloud are in phonology and semantics.

It has been argued that normal reading and acquired dyslexias reflect the role of three underlying primary systems (phonology, semantics, and vision) rather than neural mechanisms dedicated to reading. This proposal is potentially consistent with the suggestion that phonological and deep dyslexia represent variants of a single reading disorder rather than two separate entities. The current study explored this possibility, the nature of any continuum between the disorders, and the possible underlying bases of it. A case series of patients were given an assessment battery to test for the characteristics of phonological and deep dyslexia. The status of their underlying phonological and semantic systems was also investigated. The majority of participants exhibited many of the symptoms associated with deep dyslexia whether or not they made semantic errors. Despite wide variation in word and nonword reading accuracy, there was considerable symptom overlap across the cohort and, thus, no sensible dividing line to separate the participants into distinct groups. The patient data indicated that the deep-phonological continuum might best be characterized according to the severity of the individual's reading impairment rather than in terms of a strict symptom succession. Assessments of phonological and semantic impairments suggested that the integrity of these primary systems underpinned the patients' reading performance. This proposal was supported by eliciting the symptoms of deep-phonological dyslexia in nonreading tasks.

Aged↗

PubMed1998

Semantic and visual determinants of face recognition in a prosopagnosic patient.

Prosopagnosia is the neuropathological inability to recognize familiar people by their faces. It can occur in isolation or can coincide with recognition deficits for other nonface objects. Often, patients whose prosopagnosia is accompanied by object recognition difficulties have more trouble identifying certain categories of objects relative to others. In previous research, we demonstrated that objects that shared multiple visual features and were semantically close posed severe recognition difficulties for a patient with temporal lobe damage. We now demonstrate that this patient's face recognition is constrained by these same parameters. The prosopagnosic patient ELM had difficulties pairing faces to names when the faces shared visual features and the names were semantically related (e.g., Tonya Harding, Nancy Kerrigan, and Josee Chouinard -three ice skaters). He made tenfold fewer errors when the exact same faces were associated with semantically unrelated people (e.g., singer Celine Dion, actress Betty Grable, and First Lady Hillary Clinton). We conclude that prosopagnosia and co-occurring category-specific recognition problems both stem from difficulties disambiguating the stored representations of objects that share multiple visual features and refer to semantically close identities or concepts.

Aged↗

PubMed1989

Reading comprehension in adolescents with learning disabilities: semantic and syntactic effects.

Ninety-two adolescents with learning disabilities were randomly assigned to four groups to determine the effects of semantic and syntactic complexity on the reading comprehension of content area prose. One group served as a control and read a social studies passage without change. The three treatment groups read passages with syntactic and/or semantic modifications. Comprehension was significantly better for those groups reading passages with combined semantic and syntactic modifications and syntactic modifications alone, when compared to the control group. Semantic modifications alone did not significantly improve comprehension.

Adolescent↗

PubMed2005

Frontotemporal dementia, semantic dementia, and Alzheimer's disease: the contribution of standard neuropsychological tests to differential diagnosis.

CERAD-NAB (Consortium to Establish a Registry for Alzheimer's Disease-Neuropsychological Assessment Battery) data were compared between 51 patients with frontotemporal dementia, 13 with semantic dementia, and 69 with Alzheimer's disease. There were statistically significant differences between the 3 groups. Compared with patients with Alzheimer's disease, patients with frontotemporal dementia were more impaired on Animal Fluency but not on any other CERAD-NAB subtest. Patients with semantic dementia performed worse in Animal Fluency and Boston Naming Test compared with frontotemporal dementia and Alzheimer's disease. Multiple logistic regression analysis revealed that in the differentiation between frontotemporal dementia and Alzheimer's disease, the combination of Animal Fluency and Boston Naming Test correctly classified 90.5% of patients. In segregating semantic dementia and Alzheimer's disease, the combination of Boston Naming Test and Mini Mental State Examination resulted in a correct classification of 96.3%. These findings demonstrate that the Mini Mental State Examination and the language subtests of the CERAD-NAB are valuable clinical instruments for the differential diagnosis between early frontotemporal dementia, semantic dementia, and Alzheimer's disease.

Aged↗

PubMed2006

Disordered semantic representation in schizophrenic temporal cortex revealed by neuromagnetic response patterns.

BACKGROUND: Loosening of associations and thought disruption are key features of schizophrenic psychopathology. Alterations in neural networks underlying this basic abnormality have not yet been sufficiently identified. Previously, we demonstrated that spatio-temporal clustering of magnetic brain responses to pictorial stimuli map categorical representations in temporal cortex. This result has opened the possibility to quantify associative strength within and across semantic categories in schizophrenic patients. We hypothesized that in contrast to controls, schizophrenic patients exhibit disordered representations of semantic categories. METHODS: The spatio-temporal clusters of brain magnetic activities elicited by object pictures related to super-ordinate (flowers, animals, furniture, clothes) and base-level (e.g. tulip, rose, orchid, sunflower) categories were analysed in the source space for the time epochs 170-210 and 210-450 ms following stimulus onset and were compared between 10 schizophrenic patients and 10 control subjects. RESULTS: Spatio-temporal correlations of responses elicited by base-level concepts and the difference of within vs. across super-ordinate categories were distinctly lower in patients than in controls. Additionally, in contrast to the well-defined categorical representation in control subjects, unsupervised clustering indicated poorly defined representation of semantic categories in patients. Within the patient group, distinctiveness of categorical representation in the temporal cortex was positively related to negative symptoms and tended to be inversely related to positive symptoms. CONCLUSION: Schizophrenic patients show a less organized representation of semantic categories in clusters of magnetic brain responses than healthy adults. This atypical neural network architecture may be a correlate of loosening of associations, promoting positive symptoms.

Adult↗

PubMed2006

fMRI of lexical-semantic priming in a chronic schizophrenia patient.

A neuropsychological hallmark of schizophrenia is a breakdown in semantic association networks that often impacts language and formal thought. Although computational models simulating this breakdown exist, studies have yet to investigate this phenomena using functional MRI (fMRI) coupled with an auditory lexical-decision semantic priming paradigm. Thus, this serves to functionally map brain activation to word pairs that differed with respect to a concept called "connectivity" in a patient with schizophrenia and a demographically matched control adult. Analyses revealed a striking difference with respect to the expected stepwise modulation of activation, with the control participant showing significantly greater areas of modulation than the participant with schizophrenia in regions classically implicated in language. Although the results are tentative because of the nature of this investigation (single-case study), they further support the characterization of schizophrenia as a breakdown in lexical-semantic association networks and represent one of the first fMRI studies of semantic priming in schizophrenia informed by a computer model.

Brain↗

PubMed2003

Semantic priming in the name retrieval of objects and famous faces.

Researchers interested in face processing have recently debated whether access to the name of a known person occurs in parallel with retrieval of semantic-biographical codes, rather than in a sequential fashion. Recently, Schweinberger, Burton, and Kelly (2001) took a failure to obtain a semantic context effect in a manual syllable judgment task on names of famous faces as support for this position. In two experiments, we compared the effects of visually presented categorically related prime words with either objects (e.g. prime: animal; target: dog) or faces of celebrities (e.g. prime: actor; target: Bruce Willis) as targets. Targets were either manually categorized with regard to the number of syllables (as in Schweinberger et al.), or they were overtly named. For neither objects nor faces was semantic priming obtained in syllable decisions; crucially, however, priming was obtained when objects and faces were overtly named. These results suggest that both face and object naming are susceptible to semantic context effects.

Adult↗

PubMed2005

Naming very familiar people: when retrieving names is faster than retrieving semantic biographical information.

One of the most reliable findings in the literature on person indentification is that semantic categorization of a face occurs more quickly than naming a face. Here we present two experiments in which participants are shown the faces of their colleagues, i.e., personally familiar people, encountered with high frequency. In each experiment, naming was faster than making a semantic classification, despite the fact that the semantic classifications were highly salient to the participants (Experiment 1: highest degree obtained; Experiment 2: nationality). The finding is consistent with models that allow or parallel access from faces to semantic information and to names, and demonstrates the need for the frequency of exposure to names to be taken into account in models of proper name processing e.g. Burke, Mackay, Worthley and Wade (1991).

Adult↗

PubMed2004

Semantic and phonological loop effects on verbal working memory in middle-age adults with mental retardation.

Semantic and phonological loop effects on verbal working memory were examined among middle-age adults with Down syndrome and those with unspecified mental retardation in the context of Baddeley's working memory model. Recall was poorer for phonologically similar, semantically similar, and long words compared to recall of dissimilar short words. Compared to their peers, participants with Down syndrome had poorer recall in all categories except phonologically similar words. Most interestingly, semantic similarity lowered recall scores only in participants with Down syndrome. This selective effect of semantics reflects an influence of long-term memory on working memory and points to the need for additional explanations outside phonological loop processes to completely account for the relative impairment of verbal working memory among individuals with Down syndrome.

Adult↗

PubMed1999

Interaction of cortex and hippocampus in a model of amnesia and semantic dementia.

We describe a systems-level computational model, called TraceLink, that can explain the major characteristics of the neuropsychology of amnesia and of semantic dementia, a recently discovered syndrome in which there is a progressive loss of semantic memory. It also approximates the normal forgetting curve and presents an explanation of why spaced learning is more efficient than massed learning. A central assumption is that consolidation of memory takes place, probably during dream sleep. The model consists of three systems: trace system (certain parts of the neocortex), link system (includes the hippocampus), and the modulatory system (includes certain basal forebrain nuclei). Lesioning each of these causes a characteristic form of amnesia or semantic dementia. Lesioning the modulatory system causes anterograde amnesia only. Lesioning the link system causes a correlated degree of retrograde and anterograde amnesia. Retrograde amnesia shows the characteristic Ribot curve with relative sparing of remote memories but loss of recent ones. Lesioning the trace system causes semantic dementia. We also review the main sources of constraints for the model and discuss its status and function as well as its falsifiability.

Amnesia↗

PubMed2005

Neural correlates of relational memory: successful encoding and retrieval of semantic and perceptual associations.

Using event-related functional magnetic resonance imaging, we identified brain regions involved in successful relational memory (RM) during encoding and retrieval for semantic and perceptual associations or in general, independent of phase and content. Participants were scanned while encoding and later retrieving associations between pairs of words (semantic RM) or associations between words and fonts (perceptual RM). Encoding success activity (ESA) was identified by comparing study-phase activity for items subsequently remembered (hits) versus forgotten (misses) and retrieval success activity (RSA) by comparing test-phase activity for hits versus misses. The study yielded three main sets of findings. First, ESA-RSA differences were found within the medial temporal lobes (MTLs) and within the prefrontal cortex (PFC). Within the left MTL, ESA was greater in the anterior hippocampus, and RSA was greater in the posterior parahippocampal cortex/hippocampus. This finding is consistent with the notion of an encoding-retrieval gradient along the longitudinal MTL axis. Within the left PFC, ESA was greater in ventrolateral PFC, and RSA was greater in dorsolateral and anterior PFC. This is the first evidence of a dissociation in successful encoding and retrieval activity within left PFC. Second, consistent with the transfer-appropriate processing principle, some ESA regions were reactivated during RSA in a content-specific manner. For semantic RM, these regions included the left ventrolateral PFC, whereas for perceptual RM, they included occipitoparietal and right parahippocampal regions. Finally, only one region in the entire brain was associated with RM in general (i.e., for both semantic and perceptual ESA and RSA): the left hippocampus. This finding highlights the fundamental role of the hippocampus in RM.

Adolescent↗

PubMed2001

Lateral asymmetries in attentional priming during a semantic and a visuospatial task.

This study tests the hypothesis that lateral cueing of attention activates the contralateral hemisphere and also that performance on a semantic and a visuospatial task will differentially be affected depending on the visual field (right or left) to which attention was drawn. In an experimental setting, 68 subjects performed both a semantic and a visuospatial discriminating task, whereby visual priming signals unbeknownst were presented to either the left or the right visual field. For the semantic task (which is believed to engage primarily the left hemisphere) priming signals enhanced performance more when they were presented to the right visual field. For the visuospatial task, no difference was found between priming signals presented in either visual field. While there may be several alternative explanations for the observed difference in the effects of the priming signals presented to different visual fields, the importance of separating the components inherent in the tasks is stressed. While the process of decision-making may involve different relative activation of the two hemispheres, depending on whether the stimuli are semantic or visuospatial in nature, performance on the task also involves manual coordination which will depend especially on motor activation in the left hemisphere.

Adult↗

PubMed2000

Semantic category discrimination and N400.

14 subjects performed a semantic category-discrimination task in which they were presented pairs of words and asked to judge whether these belonged to the same category. Three semantic distance conditions, established for the word pairs on the basis of a survey, were semantically close condition (mammals and birds condition) and two semantically distant conditions (mammals and tools condition and birds and tools condition). The reaction times and the percentage of errors were significantly greatest for the mammals and bird condition. There were no significant differences among the three different conditions in N400 latency for target, but the amplitude of N400 tended to be largest for the mammal and bird condition. Comparison N400 of prime and target for each of the conditions showed that the latency for prime was longer than for target in all three conditions.

Adult↗

PubMed2005

Limitations of semantic priming procedures for automatic goal activation.

According to the auto-motive model, behavioral goals can be automatically activated by situational cues and may subsequently guide behavior without individual awarness. Semantic priming has become a popular paradigm for investigating effects of automatic goal activation. Nevertheless, a critical assumption of the model, i.e., that goals can be activated by semantic primes related to situational features associated with the goal, is often assumed rather than tested in experiments using semantic priming procedures. Results of four studies testing the potential of such a prime for goal activation by assessing emotional responses, subjective goal importance, behavioral intentions, and enhanced perception of goal-related stimuli do not support this assumption. The implications of these findings and a critical evaluation of results of other studies are discussed in terms of possible limitations of semantic priming procedures for testing hypotheses derived from the auto-motive model.

Adolescent↗

PubMed1987

Neuroelectric correlates of a neuropsychological model of word decoding and semantic processing in reading disabled children.

The purpose of this study was to distinguish the characteristics and components of event related potentials (ERPs) correlated with word decoding and semantic processing in a subgroup of children with specific reading disabilities related to visual processing deficiencies. The results were compared with those obtained from a group of normal readers previously studied (Ostrosky et al. in press). Visual ERPs were recorded to four stimuli: three physically different but with the same semantic content: a frequently used noun written in capitals (COCHE), the same noun in handwriting, the pictorial representation of the noun (drawing), and a neutral stimulus consisting of a checkerboard. Four derivations were used: occipital (O1-O2) and parietal (P3-P4) with reference to linked mastoids. Data were analyzed using multivariate procedures. A Principal Component Analysis with Varimax rotation of the solution was applied. In the normal readers, we found some components in the occipital derivations which identified the words presented in different styles of handwriting and others which seemed to identify these words with the pictorial representation (and not with the neutral stimuli). The first "verbal" components were situated around the 156-256 ms latency range and the second "semantic" components were observed at over 380 ms. In the disabled readers, there was no "verbal" or "semantic" recognition grouping of these physically different stimuli. As opposed to the normal readers, interhemispheric responses were symmetrical. At the left parietal leads in the normal readers, the morphology of the verbal stimuli (capitals and handwriting) were very similar throughout the sweep and both were very different from the nonverbal stimuli. At 376 ms the four stimuli elicited a prominent negative peak in which the verbal stimuli elicited significantly higher amplitude than the nonverbal stimuli. In the disabled group, the morphologies of the four stimuli were very similar and no significant differences were observed. The results are discussed in accordance with a hypothetical model of the neural bases underlying reading. The model takes into account the complexity of the reading process and the various cognitive skills required for its adequate performance, and emphasizes a complex, dynamic interplay between occipital, parietal and temporal areas.

Cerebral Cortex↗

PubMed1989

Conversational characteristics of children with semantic-pragmatic disorder. I: Exchange structure, turntaking, repairs and cohesion.

Conversational samples were obtained from 57 children aged from 8 to 12 years with specific language impairment, and 67 control children aged from 4 to 12 years. Fourteen of the language-impaired children fitted the clinical description of semantic-pragmatic disorder. It was found that exchange structure, turntaking, conversational repair and use of cohesive devices could be assessed with adequate inter-rater and test-retest reliability. Children with semantic-pragmatic disorder produced more initiations than other children. Some of these children also violated turntaking rules by interrupting the conversational partner to an unusual degree. Use of cohesion was normal for children with semantic-pragmatic disorder, but limited in other language-impaired children. Analysis of conversations may be more useful than conventional language tests for identifying linguistic abnormalities in children with semantic-pragmatic disorder.

Child↗

PubMed1989

Conversational characteristics of children with semantic-pragmatic disorder. II: What features lead to a judgement of inappropriacy?

Independent raters scanned transcribed conversations from 57 language-impaired children and 67 control children aged from 4 to 12 years and identified instances where the normal flow of conversation appeared to be disrupted because the child's utterance was in some way inappropriate. It was found that adequate inter-rater reliability could be obtained using this procedure. Furthermore, test-retest correlations for inappropriacy were significant, indicating that this is a stable conversational characteristic. The measure of inappropriacy decreased with age in control children, and it distinguished language-impaired from control children. Those identified as having 'semantic-pragmatic disorder' obtained particularly high scores. In a subsidiary analysis, inappropriate responses were subcategorised. A wide range of semantic, syntactic and pragmatic peculiarities was identified as leading to a sense of inappropriacy. Some instances of inappropriacy appeared to indicate cognitive rather than linguistic difficulties. Children with semantic-pragmatic disorder resembled younger normal children in that they frequently misunderstood the literal or implicit meaning of adult utterances and they violated normal rules of exchange structure. In other respects, however, the semantic-pragmatic group did not resemble normally developing children of any age. In particular, they tended to provide the listener with too much or too little information.

Child↗

PubMed1989

Category-specific treatment of a lexical-semantic deficit: a single case study of global aphasia.

The aim of this study was to improve the comprehension of single items in a subject with global aphasia. Existing models of semantic organisation were used to inform and guide the treatment programme. Detailed pre-therapy testing suggested a severe comprehension deficit with an inability to obtain a precise semantic specification of the items, irrespective of modality of input. A category-specific hierarchical treatment programme including generic and specific details about items was implemented through various exercises and drills. Post-therapy testing revealed a significant improvement on treated and untreated items of treated categories but limited generalisation to items in untreated categories. Improvement in the subject's general semantic abilities was also documented following treatment. The results, which are shown to be a direct consequence of the intervention programme, lend support to the categorical and hierarchical view of the organisation of semantics and provide a basis for future rehabilitation studies in this area.

Aphasia↗