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At least 73 records · Page 4Linked to original sources

PubMed2000

The impact of semantic memory impairment on spelling: evidence from semantic dementia.

We assessed spelling and reading abilities in 14 patients with semantic dementia (with varying degrees of semantic impairment) and 24 matched controls, using spelling-to-dictation and single-word reading tests which manipulated regularity of the correspondences between spelling and sound, and word frequency. All of the patients exhibited spelling and reading deficits, except at the very earliest stages of disease. Longitudinal study of seven of the patients revealed further deterioration in spelling, reading, and semantic memory. The performance of both subject groups on both spelling and reading was affected by regularity and word frequency, but these effects were substantially larger for the patients. Spelling of words with exceptional (or more precisely, unpredictable) sound-to-spelling correspondences was most impaired, and the majority of errors were phonologically plausible renderings of the target words. Reading of low frequency words with exceptional spelling-to-sound correspondences was also significantly impaired. The spelling and reading deficits were correlated with, and in our interpretation are attributed to, the semantic impairment.

Alzheimer Disease↗

PubMed2001

What's left if the Jabberwock gets the semantics? An ERP investigation into semantic and syntactic processes during auditory sentence comprehension.

This study examined auditory ERP responses to syntactic phrase structure violations occurring either in sentences containing regular words or in sentences in which content words had been replaced by pseudowords while retaining morphological markers (so-called jabberwocky sentences). Syntactic violations were found to elicit an early anterior negativity followed by a P600 for both types of sentences, suggesting that the syntactic processes in question are independent of the presence of lexical-semantic information. In syntactically correct sentences, content words in regular sentences elicited an N400 component while their pseudoword place-holders in jabberwocky sentences did not. By contrast, in syntactically incorrect sentences neither sentence type showed an N400 for the word creating the syntactic violation, indicating that the detection of a syntactic error at an early stage blocks semantic integration processes in regular sentences. We discuss these results and findings from related studies in the light of a timing hypothesis of syntactic and semantic information processing and propose that syntactic information extracted particularly early can affect semantic processes while syntactic information extracted relatively late cannot.

Adult↗

PubMed2003

The basal ganglia and semantic engagement: potential insights from semantic priming in individuals with subcortical vascular lesions, Parkinson's disease, and cortical lesions.

The impact of basal ganglia dysfunction on semantic processing was investigated by comparing the performance of individuals with nonthalamic subcortical (NS) vascular lesions, Parkinson's disease (PD), cortical lesions, and matched controls on a semantic priming task. Unequibiased lexical ambiguity primes were used in auditory prime-target pairs comprising 4 critical conditions; dominant related (e.g., bank-money), subordinate related (e.g., bank-river), dominant unrelated (e.g., foot-money) and subordinate unrelated (e.g., bat-river). Participants made speeded lexical decisions (word/nonword) on targets using a go-no-go response. When a short prime-target interstimulus interval (ISI) of 200 ms was employed, all groups demonstrated priming for dominant and subordinate conditions, indicating nonselective meaning facilitation and intact automatic lexical processing. Differences emerged at the long ISI (1250 ms), where control and cortical lesion participants evidenced selective facilitation of the dominant meaning, whereas NS and PD groups demonstrated a protracted period of nonselective meaning facilitation. This finding suggests a circumscribed deficit in the selective attentional engagement of the semantic network on the basis of meaning frequency, possibly implicating a disturbance of frontal-subcortical systems influencing inhibitory semantic mechanisms.

Acoustic Stimulation↗

PubMed1992

How semantic is automatic semantic priming?

Priming for semantically related concepts was investigated using a lexical decision task designed to reveal automatic semantic priming. Two experiments provided further evidence that priming in a single presentation lexical decision task (McNamara & Altarriba, 1988) derives from automatic processes. Mediated priming, but no inhibition or backward priming was found in this type of lexical decision task. Experiments 3 and 4 demonstrated that automatic priming was found only for associated word pairs, as determined by word association norms, and not for word pairs that are semantically related but not associated. It is argued that automatic priming in the lexical decision task occurs at a lexical level not at a semantic level.

Adult↗

PubMed2004

Puzzling thoughts for H. M.: can new semantic information be anchored to old semantic memories?

Researchers currently debate whether new semantic knowledge can be learned and retrieved despite extensive damage to medial temporal lobe (MTL) structures. The authors explored whether H. M., a patient with amnesia, could acquire new semantic information in the context of his lifelong hobby of solving crossword puzzles. First, H. M. was tested on a series of word-skills tests believed important in solving crosswords. He also completed 3 new crosswords: 1 puzzle testing pre-1953 knowledge, another testing post-1953 knowledge, and another combining the 2 by giving postoperative semantic clues for preoperative answers. From the results, the authors concluded that H. M. can acquire new semantic knowledge, at least temporarily, when he can anchor it to mental representations established preoperatively.

Aged↗

PubMed2003

The role of semantic complexity in treatment of naming deficits: training semantic categories in fluent aphasia by controlling exemplar typicality.

The effect of typicality of category exemplars on naming was investigated using a single subject experimental design across participants and behaviors in 4 patients with fluent aphasia. Participants received a semantic feature treatment to improve naming of either typical or atypical items within semantic categories, while generalization was tested to untrained items of the category. The order of typicality and category trained was counterbalanced across participants. Results indicated that patients trained on naming of atypical exemplars demonstrated generalization to naming of intermediate and typical items. However, patients trained on typical items demonstrated no generalized naming effect to intermediate or atypical examples. Furthermore, analysis of errors indicated an evolution of errors throughout training, from those with no apparent relationship to the target to primarily semantic and phonemic paraphasias. Performance on standardized language tests also showed changes as a function of treatment. Theoretical and clinical implications regarding the impact of considering semantic complexity on rehabilitation of naming deficits in aphasia are discussed.

Aged↗

PubMed2003

The role of semantic complexity in treatment of naming deficits: training semantic categories in fluent aphasia by controlling exemplar typicality.

Aged↗

PubMed2006

Qualitatively different semantic representations for abstract and concrete words: further evidence from the semantic reading errors of deep dyslexic patients.

This paper presents an investigation of the hypothesis that conceptual knowledge for abstract and concrete items is underpinned by qualitatively different representational frameworks (Crutch and Warrington, 2005a). A re-analysis of the semantic reading errors of four deep dyslexic patients is presented, examining the incidence of semantically associated and semantically similar errors in response to abstract and concrete target words. The results demonstrate that abstract target words elicit a greater proportion of associative than similar errors, while concrete words show the reverse pattern. These findings provide evidence which converges with that previously documented for a semantic refractory access dysphasic to suggest that abstract concepts are represented in an associative network while concrete concepts are represented in a categorical framework.

Adult↗

PubMed2005

Preserved reading aloud with semantic deficits: evidence for a non-semantic lexical route for reading Chinese.

This article describes a Cantonese dyslexic patient with a dissociation between reading ability and oral naming, similar to previously reported cases of Chinese dyslexia. Additional semantic tests without pictorial input were given to localize his impairment to the semantic system. His largely preserved reading performance vis-à-vis semantic deficits, together with the absence of assembled phonology in Chinese, support a model of the Chinese lexicon in which reading can be achieved via two different lexical routes, one with semantic mediation and one without. The patient's poor ability to make homophony judgments of written characters and the high rate of tonal errors suggest that brain injury may have a more detrimental effect on suprasegmental than segmental features of phonological representations.

Asian People↗

PubMed2005

Derived stimulus relations, semantic priming, and event-related potentials: testing a behavioral theory of semantic networks.

Derived equivalence relations, it has been argued, provide a behavioral model of semantic or symbolic meaning in natural language, and thus equivalence relations should possess properties that are typically associated with semantic relations. The present study sought to test this basic postulate using semantic priming. Across three experiments, participants were trained and tested in two 4-member equivalence relations using word-like nonsense words. Participants also were exposed to a single- or two-word lexical decision task, and both direct (Experiment 1) and mediated (Experiments 2 and 3) priming effects for reaction times and event-related potentials were observed within but not across equivalence relations. The findings support the argument that derived equivalence relations provides a useful preliminary model of semantic relations.

Adolescent↗

PubMed2004

Identifying reading strategies using latent semantic analysis: comparing semantic benchmarks.

We explored methods of using latent semantic analysis (LSA) to identify reading strategies in students' self-explanations that are collected as part of a Web-based reading trainer. In this study, college students self-explained scientific texts, one sentence at a time. ISA was used to measure the similarity between the self-explanations and semantic benchmarks (groups of words and sentences that together represent reading strategies). Three types of semantic benchmarks were compared: content words, exemplars, and strategies. Discriminant analyses were used to classify global and specific reading strategies using the LSA cosines. All benchmarks contributed to the classification of general reading strategies, but the exemplars did the best in distinguishing subtle semantic differences between reading strategies. Pragmatic and theoretical concerns of using LSA are discussed.

Adult↗

PubMed2001

Semantic knowledge and episodic memory for faces in semantic dementia.

Previous studies have documented poor recognition memory for faces in patients with semantic dementia. Preserved face recognition memory was found in this study, however, so long as atrophy was confined predominantly to the left temporal lobe. Patients with structural damage to the right temporal lobe were typically impaired, with the status of the hippocampus and parahippocampal gyrus (including the perirhinal cortex) on the right being critical. Two single-case studies of patients with predominantly left temporal lobe pathology confirmed good recognition memory for famous faces, even if semantic knowledge about the celebrities depicted was severely degraded. An effect of semantic knowledge on recognition memory became apparent only when perceptually different photographs of the famous people were used at study and test. These results support the view that new episodic learning typically draws on information from both perceptual and semantic systems.

Aged↗

PubMed2006

'Non-semantic' aspects of language in semantic dementia: as normal as they're said to be?

This article describes a 52-month longitudinal study of a patient, ILJ, whose semantic profile fits the criteria for a classical case of semantic dementia (SD). As in all such cases, it was the semantic aspects of receptive and expressive language processing--essentially vocabulary--that were most dramatically affected. The novel observation from this study is ILJ's performance on a comprehensive language examination. Results from this assessment, even early in the course of his disease, are compatible with the hypothesis that phonological, morphological and/or syntactic aspects of language processing may be disrupted by their interaction with degraded information from the semantic system.

Atrophy↗

PubMed1998

Bilingual aphasia: semantic organization, strategy use, and productivity in semantic verbal fluency.

A semantic verbal fluency task (Animals, Foods) was administered to 16 aphasic, bilingual adults in French and English. Each subject was tested twice in each language. The two goals of the study were to compare performance across languages and to determine the effect of a deliberate grouping strategy on productivity. All subjects claimed approximately equal prestroke abilities in both languages. The number of words subjects produced was not significantly different in the two languages. Semantic organization across languages was also similar on Test 1. On Test 2, 8 subjects were instructed to group items by subcategory and 8 simply repeated the task. There was no consistent between-group difference in number of correct words or in the semantic organization of responses. Implications for the clinical use of verbal fluency tests and for further research into bilingual lexicosemantic systems are discussed.

Adult↗

PubMed1998

The effects of semantic category and knowledge type on lexical-semantic access: a PET study.

Neuropsychological studies of patients with category-specific recognition disorders, as well as PET investigations of semantic category effects in visual recognition tasks, have led some authors to the hypothesis that visual-perceptual knowledge plays a crucial role in the recognition of natural items, such as animals, while functional-associative information is more important for the recognition of man-made tools. To study the cerebral correlates of the retrieval of different types of semantic knowledge about living and nonliving entities, we performed a PET experiment in which normal subjects were required to access visual- and functional-associative information related to visually presented words corresponding to animals and tools. The experimental conditions were the following: (1) Rest. (2) Baseline: letter detection in pseudo-words. (3) Animal, visual knowledge: decide whether the animal has a long or short tail with respect to the body. (4) Animal, associative knowledge: decide whether the animal is typically found in Italy. (5) Tool, visual knowledge: decide whether the object is longer than wider or vice versa. (6) Tool, functional knowledge: decide whether the object is typically used as a kitchen tool. Lexical-semantic access (all lexical conditions pooled) activated the prefrontal cortex on the left and the parietal-occipital junction and posterior cingulate cortex bilaterally. An analysis of the individual experimental conditions in comparison with the nonword baseline showed that accessing visual versus associative knowledge was associated with different activation patterns: predominantly frontal in the case of visual features, temporoparietal for associative knowledge. While the activation patterns involved similar areas for living and nonliving entities, in the case of the latter they were restricted to the left hemisphere. The analysis of main effects confirmed these findings: there were several significant differences in the visual-associative comparison, while category-related differences were less prominent. These findings indicate that the retrieval of different types of knowledge is associated with distinct patterns of brain activation; on the other hand, category-related differences were less evident than in picture matching and naming tasks.

Adult↗

PubMed1989

Semantic abilities in dementia of the Alzheimer type. 1. Lexical semantics.

The lexical semantic abilities of 18 Alzheimer patients were investigated using confrontation naming tasks (including both visual and tactile naming tests) and compared to those of a group of institutionalized, nonneurologically impaired control subjects matched for age, sex, and educational level. The Alzheimer patients produced a greater number of naming errors than the control subjects. The errors made by subjects during the naming tasks were analyzed according to a set of 16 error response types. The Alzheimer patients' response patterns suggest that they do recognize objects which they are unable to name and are able to identify the semantic class to which the target belongs, but cannot provide the lexeme corresponding to the correct individual class member. The results support a semantic network disruption rather than a visual perceptual deficit as the basis of the naming disturbance observed in Alzheimer patients.

Aged↗

PubMed2005

Testing the limits of the semantic illusion phenomenon: ERPs reveal temporary semantic change deafness in discourse comprehension.

In general, language comprehension is surprisingly reliable. Listeners very rapidly extract meaning from the unfolding speech signal, on a word-by-word basis, and usually successfully. Research on 'semantic illusions' however suggests that under certain conditions, people fail to notice that the linguistic input simply doesn't make sense. In the current event-related brain potentials (ERP) study, we examined whether listeners would, under such conditions, spontaneously detect an anomaly in which a human character central to the story at hand (e.g., "a tourist") was suddenly replaced by an inanimate object (e.g., "a suitcase"). Because this replacement introduced a very powerful coherence break, we expected listeners to immediately notice the anomaly and generate the standard ERP effect associated with incoherent language, the N400 effect. However, instead of the standard N400 effect, anomalous words elicited a positive ERP effect from about 500-600 ms onwards. The absence of an N400 effect suggests that subjects did not immediately notice the anomaly, and that for a few hundred milliseconds the comprehension system has converged on an apparently coherent but factually incorrect interpretation. The presence of the later ERP effect indicates that subjects were processing for comprehension and did ultimately detect the anomaly. Therefore, we take the absence of a regular N400 effect as the online manifestation of a temporary semantic illusion. Our results also show that even attentive listeners sometimes fail to notice a radical change in the nature of a story character, and therefore suggest a case of short-lived 'semantic change deafness' in language comprehension.

Adult↗

PubMed2006

Electroencephalography effects to semantic and non-semantic mismatch in properties of visually presented single-characters: the N2b and the N400.

Event-related potential (ERP) correlates of semantic and non-semantic mismatch in the 200-400ms time interval were dissociated. Twelve subjects observed pairs of single letters and digits presented serially, and decided whether the colour (blue or red) or the category membership (letter or number) of the second item in a pair matched the first one. In both tasks mismatch elicited central N2b components (220ms peak latency in the colour matching task, and 280ms peak latency in the category matching task). Furthermore, in the category matching task a centro-parietal negativity (N400) emerged. The topography of the N2b effect was clearly distinct from that of the N400 effect. Analysis of event-related spectral perturbations confirmed that N400 time-range effects were specific to category matching. We conclude that while the N400 effect is a specific marker of semantic mismatch, the N2b effect is a general correlate of detecting mismatch between the representations of task-relevant features.

Adolescent↗