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At least 19 recordsLinked to original sources
PubMed2003

Semantically convergent and semantically divergent priming in the cerebral hemispheres: lexical decision and semantic judgment.

The effects of semantically divergent and semantically convergent priming on the processing of lexical ambiguity by the two cerebral hemispheres were examined in two visual hemifield experiments. The experiments investigated the ability of the right hemisphere (RH) and the left hemisphere (LH) to summate activation from two single word primes followed by a laterally presented ambiguous target word. In a lexical decision task (experiment 1), the two priming words were either both related to the dominant meaning of the target (new, fresh-NOVEL), or to the subordinate meaning (story, book-NOVEL), or to one dominant and one subordinate meaning (new, story-NOVEL). Results indicated that the LH benefited most from semantically convergent primes that converged onto the dominant meaning of the ambiguous target word, whereas the RH benefited most from semantically mixed (divergent) primes, that diverge on alternate meanings of the ambiguous target word. We used the same stimuli in a semantic relatedness judgment task (experiment 2), and found that the facilitation in the RH was significantly larger when the primes were mixed than when both primes converged on a single (i.e. either dominant or subordinate) meaning of the to-be-presented target word. In contrast, the only facilitation found in the LH was when the two primes were associated with a single meaning (either dominant or subordinate) of the to-be-presented target word. When the primes were mixed, there was no facilitation in the LH. These results support previous findings indicating that during word recognition, the RH activates a broader range of related meanings than the LH, including alternate meanings of ambiguous words. Thus, by summating activation for seemingly incongruous elements, the RH may be critically involved in at least one important component of verbal creativity.

Adolescent↗
PubMed2003

Semantics and semantic errors: implicit access to semantic information from words and nonwords in deep dyslexia.

In this paper we describe dissociations of implicit versus explicit access to semantic information in a patient with deep dyslexia. This acquired reading disorder is characterized by the production of morphological (e.g., SLEEP read as SLEEPING) and semantic errors (e.g., HEART read as BLOOD) and consequently provides a potential window into the operation of both aspects of the language system. The deep dyslexic patient in this study (JO) demonstrated implicit semantic access to items in a number of tasks despite the fact that she was unable to correctly read these items aloud. The findings from this study are consistent with a model of lexical deficits that distinguishes between explicit and implicit access to lexical representations on the basis of inhibitory processes.

Dyslexia↗
PubMed2004

[Semantic memory in Alzheimer's disease: contributions of semantic priming].

Patients with Alzheimer's disease can be affected by semantic memory disorders from the onset of the dementia. Knowing precisely these disorders is important to improve the early diagnosis of Alzheimer's disease. Classical tests of semantic memory, such as naming and verbal fluency, highlight the existence of semantic disorders in the first stages of the disease. However, these tasks are not specific and involve cognitive processes (working memory, attentional resources), which are often disturbed in Alzheimer's disease. Therefore, they cannot attest the origin of the semantic disorders, which can be related either to a deficit of access to stored information in a preserved semantic network, or to the deterioration of the semantic memory network. Semantic priming paradigms, by minimizing the intervention of processes other than semantic, constitute relevant tools to study the integrity of the semantic network. However, the results of the studies devoted to the semantic priming effects in patients suffering from Alzheimer's disease are heterogeneous. This could be imputed, in part, to differences in experimental procedures. Nevertheless, some studies, conducted with a very controlled methodology, showed that semantic relationships used in the semantic paradigm as well as the semantic deficit severity have a serious impact on semantic priming effects. Taking into account these parameters, the results of semantic priming studies are more in accordance with the assumption of a storage degradation than with an access deficit. Moreover, these studies, and especially the observation of an hyperpriming effect, allow a better understanding of how semantic memory is degraded. The progressive deterioration begins at the level of the concept attributes, and further involves the concepts themselves.

Aged↗
PubMed2005

Relationship structures and semantic type assignments of the UMLS Enriched Semantic Network.

OBJECTIVE: The Enriched Semantic Network (ESN) was introduced as an extension of the Unified Medical Language System (UMLS) Semantic Network (SN). Its multiple subsumption configuration and concomitant multiple inheritance make the ESN's relationship structures and semantic type assignments different from those of the SN. A technique for deriving the relationship structures of the ESN's semantic types and an automated technique for deriving the ESN's semantic type assignments from those of the SN are presented. DESIGN: The technique to derive the ESN's relationship structures finds all newly inherited relationships in the ESN. All such relationships are audited for semantic validity, and the blocking mechanism is used to block invalid relationships. The mapping technique to derive the ESN's semantic type assignments uses current SN semantic type assignments and preserves nonredundant categorizations, while preventing new redundant categorizations. RESULTS: Among the 426 newly inherited relationships, 326 are deemed valid. Seven blockings are applied to avoid inheritance of the 100 invalid relationships. Sixteen semantic types have different relationship structures in the ESN as compared to those in the SN. The mapping of semantic type assignments from the SN to the ESN avoids the generation of 26,950 redundant categorizations. The resulting ESN contains 138 semantic types, 149 IS-A links, 7,303 relationships, and 1,013,876 semantic type assignments. CONCLUSION: The ESN's multiple inheritance provides more complete relationship structures than in the SN. The ESN's semantic type assignments avoid the existing redundant categorizations appearing in the SN and prevent new ones that might arise due to multiple parents. Compared to the SN, the ESN provides a more accurate unifying semantic abstraction of the UMLS Metathesaurus.

Semantics↗
PubMed2006

Semantic hyperpriming in schizophrenic patients: increased facilitation or impaired inhibition in semantic association processing?

Previous studies analyzing semantic priming in schizophrenic patients have reported conflicting results. In the present study, we explored semantic priming in a sample of schizophrenic patients with mild thought disorders. We wondered if distinct cognitive processes, such as facilitation and/or inhibition, underlie semantic hyperpriming and are variously impaired in schizophrenic patients. Using a lexical decision task, we evaluated semantic priming in 15 schizophrenic patients (DSM-IV) with mild thought disorders and 15 healthy controls matched for sex, age, and education level. The task was designed to divide semantic priming into two additive components, namely facilitation effect and inhibition effect. One-sample t-tests were performed to investigate differences in semantic priming, facilitation, and inhibition within each group. ANOVAs were performed to compare the effects of semantic priming, facilitation, and inhibition between groups. Patients displayed greater semantic priming than controls (i.e., hyperpriming), but this was not due to increased facilitation in processing semantically related pairs. On the contrary, hyperpriming was the result of prolonged response time to process semantically unrelated pairs, corresponding to a requirement to inhibit unrelated information. We demonstrated semantic hyperpriming in stabilized schizophrenic patients with mild severity of symptoms. Thus, semantic hyperpriming may be an intrinsic feature of schizophrenia that is not related to the clinical state of patients. Semantic hyperpriming was due to an inhibition effect involved in processing semantically unrelated information not to increased facilitatory effect for related pairs.

Adult↗
PubMed2001

Are semantic errors actually semantic?: Evidence from alzheimer's disease.

Patients with Alzheimer's disease (AD) produce a high rate of semantic errors when naming to confrontation. This is considered to be one of the many consequences of their semantic memory deficit. However, it has been shown, in aphasic patients with focal lesions, that semantic errors could arise from impairment to any one of the levels in the naming process. To check this hypothesis in AD, we assessed in 15 patients the capacity to name and access semantic knowledge (by multiple-choice probe questions) about 14 objects presented successively in the visual, tactile, auditory, and verbal modalities. In the visual naming task, 33 errors were recorded: 26 (78.8%) were semantic and 7 (21.2%) were unrelated errors. Of the 26 semantic errors, 8 were related to a deficit of the semantic knowledge related to the item and 17 to a deficit in the retrieval of the phonological form of the word. One was associated with a deficit of access to semantic knowledge in the visual modality. The 7 unrelated errors were associated with a loss of semantic knowledge for 4 and deficit of access to the phonological form for 3. In conclusion, this study shows that semantic errors do not systematically reflect a deficit of semantic knowledge in Alzheimer's disease. It also seems that unrelated errors are more frequently related to semantic deficits than semantic errors in this population.

Aged↗
PubMed2006

Semantic impairment in stroke aphasia versus semantic dementia: a case-series comparison.

Different neuropsychological populations implicate diverse cortical regions in semantic memory: semantic dementia (SD) is characterized by atrophy of the anterior temporal lobes whilst poor comprehension in stroke aphasia is associated with prefrontal or temporal-parietal infarcts. This study employed a case-series design to compare SD and comprehension-impaired stroke aphasic patients directly on the same battery of semantic tests. Although the two groups obtained broadly equivalent scores, they showed qualitatively different semantic deficits. The SD group showed strong correlations between different semantic tasks--regardless of input/output modality--and substantial consistency when a set of items was assessed several times. They were also highly sensitive to frequency/familiarity and made coordinate and superordinate semantic errors in picture naming. These findings support the notion that amodal semantic representations degrade in SD. The stroke aphasia group also showed multimodal deficits and consistency across different input modalities, but inconsistent performance on tasks requiring different types of semantic processing. They were insensitive to familiarity/frequency--instead, tests of semantic association were influenced by the ease with which relevant semantic relationships could be identified and distractors rejected. In addition, the aphasic patients made associative semantic errors in picture naming that SD patients did not make. The aphasic patients' picture naming performance improved considerably with phonemic cues suggesting that these patients retained knowledge that could not be accessed without contextual support. We propose that semantic cognition is supported by two interacting principal components: (i) a set of amodal representations (which progressively degrade in SD) and (ii) executive processes that help to direct and control semantic activation in a task-appropriate fashion (which are dysfunctional in comprehension-impaired stroke aphasic patients).

Adult↗
PubMed2005

Mediotemporal contributions to semantic processing: fMRI evidence from ambiguity processing during semantic context verification.

The medial temporal lobe (MTL) is well known to be crucial for various types of memory; however, controversy remains as to which of its substructures contribute to semantic processing and, if so, to what extent. The current study addresses the issue of MTL contributions to semantic processing during lexico-semantic ambiguity processing by using functional magnetic resonance imaging (fMRI) in combination with a context verification task (CVT). The CVT required decisions on the semantic fit of congruent and incongruent target words to the overall meaning of preceding sentential contexts with and without semantic ambiguity. In two of the four experimental conditions (congruent homographic, incongruent homographic), target decisions were critically dependent on the successful processing of prior sentence-final lexico-semantic ambiguity. Semantic context verification per se evidenced bilateral activations of the hippocampus that were part of a functional network including inferior prefrontal and superior parietal cortices. Commonalities in activation differences pertaining to the specific cognitive component of lexico-semantic ambiguity processing were found in a left temporal lobe network that comprised activation foci in the temporal pole, the parahippocampal and fusiform gyri. The present results suggest that the hippocampus may well contribute to semantic processing, namely by a mnemonic function that serves to link the target meaning representation with the meaning of a prior sentence context. Contrary to previous reports from human lesion studies, the present findings further suggest, that the specific cognitive component of lexico-semantic ambiguity processing is neither dependent on the hippocampus nor exclusively subserved by the temporal pole, but also recruits an associative semantic memory function from the parahippocampal gyrus as well as a more general (bottom-up) semantic function from the fusiform gyrus.

Adult↗
PubMed2006

An fMRI study of semantic priming: modulation of brain activity by varying semantic distances.

OBJECTIVE: Our purpose was to study the effect of semantic priming at varying semantic distances on brain activation during a lexical decision experiment, using functional magnetic resonance imaging (fMRI). BACKGROUND: Neuroimaging studies have demonstrated decreased brain activation for primed versus unprimed stimuli in language areas due to semantic priming, suggesting facilitated semantic retrieval. However, the effect of varying semantic distances on brain activation has not been studied. Therefore we examined direct and indirect priming effects on cerebral activation to provide information regarding spread of activation in the semantic network. METHODS: Participants were presented with closely, distantly, and unrelated word pairs during fMRI, and asked to make a lexical decision on the second word. RESULTS: Behavioral measurements demonstrated significant priming effects for all semantic distances. Imaging results showed modulation of brain activation due to different semantic relationships in the left inferior frontal gyrus, bilateral middle frontal gyrus and anterior temporal lobe, and consisted of decreased magnitude of activation when primed stimuli were processed compared with unprimed stimuli, with the greatest effect observed for closely related words. CONCLUSIONS: This study demonstrates graduated effects of semantic priming on fMRI in semantic but not attentional brain regions, contributing to explain how semantic knowledge is organized and retrieved. These findings support the network model for organization of the semantic lexicon.

Adult↗
PubMedDate not supplied

Short-term retention of lexical-semantic representations: implications for speech production.

Patients with semantic STM deficits have difficulty comprehending sentences that require the retention of several lexical-semantic representations prior to their integration into higher-level propositions (Martin, 1995: Martin & Romani. 1994). In Experiment 1, patients with a semantic retention deficit had difficulty with the same type of constructions in speech production, namely noun phrases with one or two prenominal adjectives. Their performance improved when they could produce the nouns and adjectives in sentence form, which placed smaller demands on lexical-semantic retention. In Experiment 2 these patients were better able to produce syntactically complex sentences than the prenominal adjective phrases having an equal number of content words, indicating that the findings in Experiment 1 could not be attributed to syntactic complexity. These patients produced more pauses in the sentence constructions in Experiments 1 and 2, suggesting that the timing of such productions is abnormal. In contrast, patient EA, with a phonological retention deficit, performed better than the patients with a semantic retention deficit on the AN phrases despite having a smaller STM span. She showed no significant benefit of producing sentence compared to phrase constructions, and also made fewer and shorter pauses than the other patients. These findings support the multiple capacities view of verbal working memory and suggest that the same semantic retention capacity used in language comprehension is used in speech production.

Aged↗
PubMed2005

Left inferior prefrontal cortex activation during a semantic decision-making task predicts the degree of semantic organization.

Semantic organization, an aspect of semantic processing, requires a pre-existing network of semantic knowledge that relies on a widely distributed neural network. The inferior prefrontal cortex (IPFC) has been identified as a vital structure for processing competing semantic information when making a decision about the meaning of a stimulus. However, the precise role of the IPFC in maintaining or creating a consistent semantic organizational structure is unclear. In this study, a semantic triadic decision-making task (Tallent, K.A., Weinberger, D.R., and Goldberg, T.E. 2001. Associating semantic space abnormalities with formal thought disorder in schizophrenia: use of triadic comparisons. J. Clin. Exp. Neuropsychol. 285-296) was used during functional magnetic resonance imaging to test the hypothesis that the degree of activation in the IPFC correlates with the consistency of semantic organization in healthy subjects. In this sample, subjects who had greater activation in the IPFC also demonstrated smaller stress coefficients in a two-dimensional "semantic space", indicating a greater organization of words along semantic dimensions. This finding is consistent with the role of the IPFC in establishing self-generated semantic relationships between stimuli.

Adult↗
PubMed2000

Non-verbal semantic impairment in semantic dementia.

The clinical presentation of patients with semantic dementia is dominated by anomia and poor verbal comprehension. Although a number of researchers have argued that these patients have impaired comprehension of non-verbal as well as verbal stimuli, the evidence for semantic deterioration is mainly derived from tasks that include some form of verbal input or output. Few studies have investigated semantic impairment using entirely non-verbal assessments and the few exceptions have been based on results from single cases ([3]: Breedin SD, Saffran EM, Coslett HB. Reversal of the concreteness effect in a patient with semantic dementia. Cognitive Neuropsychology 1994;11:617-660, [12]: Graham KS, Becker JT, Patterson K, Hodges JR. Lost for words: a case of primary progressive aphasia? In: Parkin A, editor. Case studies in the neuropsychology of memory, East Sussex: Lawrence Erlbaum, 1997. pp. 83-110, [21]: Lambon Ralph MA, Howard D. Gogi aphasia or semantic dementia? Simulating and assessing poor verbal comprehension in a case of progressive fluent aphasia. Cognitive Neuropsychology, (in-press). This study employed sound recognition and semantic association tasks to investigate the nature of the verbal and non-verbal comprehension deficit in 10 patients with semantic dementia. The patients were impaired on both verbal and non-verbal conditions of the assessments, and their accuracy on these tasks was directly related to their scores on a range of other tests requiring access to semantic memory. Further analyses revealed that performance was graded by concept and sound familiarity and, in addition, identified significant item consistency across the different conditions of the tasks. These results support the notion that the patients' deficits across all modalities were due to degradation within a single, central network of conceptual knowledge. There were also reliable differences between conditions. The sound-picture matching task proved to be more sensitive to semantic impairment than the word-picture matching equivalent, and the patients performed significantly better on the picture than word version of a semantic association test. We propose that these differences arise directly from the nature of the mapping between input modality and semantic memory. Words and sounds have an arbitrary relationship with meaning while pictures benefit from a degree of systematicity with conceptual knowledge about the object.

Aphasia↗
PubMed2003

Interplay between syntax and semantics during sentence comprehension: ERP effects of combining syntactic and semantic violations.

This study investigated the effects of combined semantic and syntactic violations in relation to the effects of single semantic and single syntactic violations on language-related event-related brain potential (ERP) effects (N400 and P600/SPS). Syntactic violations consisted of a mismatch in grammatical gender or number features of the definite article and the noun in sentence-internal or sentence-final noun phrases (NPs). Semantic violations consisted of semantically implausible adjective-noun combinations in the same NPs. Combined syntactic and semantic violations were a summation of these two respective violation types. ERPs were recorded while subjects read the sentences with the different types of violations and the correct control sentences. ERP effects were computed relative to ERPs elicited by the sentence-internal or sentence-final nouns. The size of the N400 effect to the semantic violation was increased by an additional syntactic violation (the syntactic boost). In contrast, the size of the P600/SPS to the syntactic violation was not affected by an additional semantic violation. This suggests that in the absence of syntactic ambiguity, the assignment of syntactic structure is independent of semantic context. However, semantic integration is influenced by syntactic processing. In the sentence-final position, additional global processing consequences were obtained as a result of earlier violations in the sentence. The resulting increase in the N400 amplitude to sentence-final words was independent of the nature of the violation. A speeded anomaly detection task revealed that it takes substantially longer to detect semantic than syntactic anomalies. These results are discussed in relation to the latency and processing characteristics of the N400 and P600/SPS effects. Overall, the results reveal an asymmetry in the interplay between syntax and semantics during on-line sentence comprehension.

Adult↗
PubMed2005

Semantic memory disorders in Alzheimer's disease: clues from semantic priming effects.

Semantic memory deficits are a common landmark in Alzheimer's disease, but the nature of these impairments remains to be clarified. The tests used to explore this memory system are not specific and involve cognitive processes often disturbed in Alzheimer's disease. A complementary way to investigate semantic memory in neuropsychology is by using the semantic priming paradigm. Here, semantic priming refers specifically to the modification of a stimulus processing behind the presentation of a related stimulus; it is a short-lived phenomenon considered an implicit measure of semantic memory integrity. However, semantic priming studies have yielded contradictory results in Alzheimer's disease, with authors reporting normal priming, less-than-normal priming, or increased priming effects (hyperpriming). The aim of this paper is to review the literature investigating semantic priming in Alzheimer's disease, and to discuss the contradictory results in the context of current models of semantic processing. For a clear comprehension of the semantic priming patterns in this pathology, we will precise the methodology used and the characteristics of the Alzheimer's disease patients examined. Besides, the surprising hyperpriming phenomenon - often observed in Alzheimer's disease at the early stage of dementia--will also be explained in detail. These results from semantic priming represent invaluable clues to widen our knowledge and conceptions about deterioration of the semantic memory in Alzheimer's disease.

Alzheimer Disease↗
PubMed2001

Abnormally increased semantic priming in children with symptomatic HIV-1 disease: evidence for impaired development of semantics?

Language deficits are a major characteristic of neurobehavioral dysfunction in pediatric HIV disease. An object decision task, which assessed reaction time facilitation following a semantic or identical prime in comparison to an unrelated prime, was used to investigate whether semantic processing abnormalities could be responsible, in part, for these deficits. Thirty children with vertically acquired HIV infection (M age 9.0 years; range 6-13) participated. Either a picture of the same object (repetition prime), a semantically related object (semantic prime), a semantically unrelated object, or a nonsense object preceded a target picture, which in 50% of the cases was a real object. Brain scans of children were rated and used together with neurobehavioral functioning to classify children as having HIV-related CNS abnormalities (n = 13) or not (n = 17). Increased semantic priming but not repetition priming was associated with a greater degree of cortical atrophy. Furthermore, CNS compromised children had significantly faster reaction times following a semantic prime compared to an unrelated prime than non-compromised patients. This facilitation following semantic priming for the CNS compromised patients (13.3%) almost equaled the facilitation following repetition priming (15.3%) while for the non-compromised patients facilitation following semantic priming (7.9%) was clearly smaller than following repetition priming (14.6%). These data suggest that HIV infection in children may result in a reduced neural network leading to impoverished semantic representations characterized by poor differentiation between closely related objects.

Acquired Immunodeficiency Syndrome↗
PubMedDate not supplied

Investigating semantic memory impairments: the contribution of semantic priming.

The semantic priming task is a valuable tool in the investigation of semantic memory impairments in patients with acquired disorders of language. This is because priming performance reflects automatic or implicit access to semantic information, unlike most other tests of semantic knowledge, which rely on explicit, voluntary access. Priming results are important for two main reasons: First, normal priming results may be observed in patients who perform poorly on other semantic memory tests, enabling us to distinguish between loss of, or damage to, information in semantic memory, and voluntary access to that information. Second, we can investigate the detailed pattern of loss and preservation of different types of semantic information, by charting the priming effects for different kinds of words, and different kinds of semantic relations between primes and targets. We discuss the use of the priming task in this context, and address some of the theoretical and methodological criticisms that have been raised in connection with use of the priming task to address these issues. We then describe two recent studies in which we have employed semantic priming tasks, along with other more traditional methods, to investigate specific questions about the semantic memory deficits of three patients.

Aged↗
PubMed2004

Deep dyslexia and semantic errors: a test of the failure of inhibition hypothesis using a semantic blocking paradigm.

Deep dyslexia is an acquired reading disorder that involves the production of semantic errors and the inability to read aloud nonwords successfully. Several explanations for this reading impairment posit multiple loci of damage to account for the various error types produced in deep dyslexia. In contrast, the failure of inhibition hypothesis suggests that damage in the phonological output lexicon alone can explain these errors. Specifically, this hypothesis proposes normal processing via orthographic and phonological reading routes, as well as an intact semantic system. However, slowed or reduced inhibitory connections result in the failure to suppress spuriously activated neighbours in the phonological output lexicon, where neighbourhood can be defined in terms of phonology, orthography, or semantics. Given a failure to inhibit semantically related candidates, semantic reading errors occur. Important to the test of this hypothesis is that it evolves several predictions that are contrary to performance observed in the normal population. In particular, semantic errors are predicted to be greater in conditions where words are blocked according to semantic category than in random presentations. In addition, a semantic interference effect is expected. The results of semantic blocking were consistent with these predictions and lend support to the failure of inhibition hypothesis.

Attention↗
PubMed2004

Physiological evidence that a masked unrelated intervening item disrupts semantic priming: implications for theories of semantic representation and retrieval models of semantic priming.

Event-related potentials were recorded in a paradigm where an unrelated word was interposed between two related words. In one condition, the intervening item was masked and in another condition it was not. The N400 component indicated that priming of the related word was disrupted by the intervening item whether it was masked or not. The data are interpreted to be inconsistent with retrieval models of priming.

Adolescent↗