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PubMed1999

A technique for semantic classification of unknown words using UMLS resources.

Natural Language Processing (NLP) is a tool for transforming natural text into codable form. Success of NLP systems is contingent on a well constructed semantic lexicon. However, creation and maintenance of these lexicons is difficult, costly and time consuming. The UMLS contains semantic and syntactic information of medical terms, which may be used to automate some of this task. Using UMLS resources we have observed that it is possible to define one semantic type by its syntactic combinations with other types in a corpus of discharge summaries. These patterns of combination can then be used to classify words which are not in the lexicon. The technique was applied to a corpus for a single semantic type and generated a list of 875 words which matched the classification criteria for that type. The words were ranked by number of patterns matched and the top 95 words were correctly typed with 80% accuracy.

Humans↗

PubMedDate not supplied

Differentiating the N3 and N4 electrophysiological semantic incongruity effects.

An event-related potential termed the N4 has been widely studied due to its sensitivity to semantic incongruity. A recent report (Nobre & McCarthy, 1994) indicates there is also an N3 component that is sensitive to semantic incongruity. To differentiate these two components, an existing data set with 65 electrode sites, 78 subjects, and 120 sentences was examined. Instead of the usual procedure of averaging over the stimuli within distinct categories for each subject, a new approach--averaging over subjects--was employed. In this item average approach, 120 averages (one per sentence) were produced. Correlational analyses indicate that the N3 is equally sensitive to cloze probability and sentential constraint. The N4, by contrast, is more sensitive to sentential constraint and less to cloze probability; it is also correlated with familiarity. We interpret these results as evidence that the N3 is more responsive to semantic fit whereas the N4 is more responsive to semantic expectancy.

Adult↗

PubMed2001

A constraint on eliminating semantic priming by repeating a prime.

Repeated semantic primes have been shown to generate an additive semantic priming effect when those primes are different words, but repetition priming of the prime seems to eliminate semantic priming of lexical decisions for reasons that are not clear. These studies replicated this effect but also showed that repetition priming of the prime does not eliminate semantic priming with a longer lag between the repeated primes. The implications of these results for understanding the basic effect are discussed.

Adult↗

PubMed2001

An early electrophysiological sign of semantic processing in basal extrastriate areas.

Recognition potential (RP), a recently discovered electrophysiological response of the brain, is sensitive to semantic aspects of stimuli. Given its peak values (about 250 ms), RP may be a good candidate for the study of semantic processing during its occurrence. However, its topography and neural generators are largely unknown. To improve this state of affairs, high-resolution electroencephalography and brain electrical source analysis were carried out. Results suggest a possible origin of RP in the lingual gyrus, hence reflecting the activity of the basal extrastriate areas. RP therefore appears to be a highly valuable tool in the study of those regions considered to be the "third language areas" (in addition to Broca's and Wernicke's areas), whose precise role in language processing is still largely unknown. Another important finding was that RP amplitude in the left hemisphere differed as a function of the semantic category of the stimuli, providing evidence for the sensitivity of this component to semantic categorization. A tentative proposal is made with regard to the role of the basal extrastriate areas.

Adult↗

PubMed2001

Methods for exploring the semantics of the relationships between co-occurring UMLS concepts.

OBJECTIVE: To characterize the relationships among UMLS concepts that co-occur as MeSH descriptors in MEDLINE citations (1990-1999). DESIGN: 18,485 UMLS concepts involved in 7,928,608 directed pairs of co-occurring concepts were studied. For each directed pair of concepts C1-C2: (i) the "family" of C1 was built, using the UMLS Metathesaurus, and we tested whether or not C2 belonged to C1's family; (ii) we used the semantic categorization of Metathesaurus concepts through the UMLS Semantic Network and Semantic Groups to represent the semantics of the relationships between C1 and C2. RESULTS: In 6.5% of the directed pairs, the co-occurring concept C2 was found within the "family" of C1. Detailed results are given. The most frequent co-occurrences involved "Chemicals and Drugs" and "Chemicals and Drugs", as well as "Disorders" and "Chemicals and Drugs". DISCUSSION: This work takes advantage of both symbolic and statistical information represented in the UMLS, and analyzes their overlap. Further research is suggested.

MEDLINE↗

PubMed2001

Semantic satiation and lexical ambiguity resolution.

This study examines the effects of semantic satiation on lexical ambiguity resolution. On a given trial, participants were presented with a word triad. The first word (e.g., HEART) was presented on average 2.5, 12.5, or 22.5 times, and then participants received 2 new words for relatedness judgments. The first of the two new words was always a homograph (e.g., "ORGAN") and the other word was a related or unrelated pairmate (e.g., "KIDNEY"). In Experiment 1, when blocks of trials were intermixed with concordant (e.g., "HEART-ORGAN-KIDNEY"), discordant (e.g., "PIANO-ORGAN-KIDNEY"), and neutral (e.g., "CEILING-ORGAN-KIDNEY") trials, participants did not produce evidence of semantic satiation. In a second experiment in which only concordant and neutral trials were presented, however, participants did produce evidence of semantic satiation in the concordant condition. Taken together, Experiments 1 and 2 indicate that semantic satiation of the context-appropriate meaning of a homograph may impede ambiguity resolution.

Analysis of Variance↗

PubMed2001

Empirical data for the semantic interpretation of prepositional phrases in medical documents.

We report on the results from an empirical study deal-ing with the semantic interpretation of prepositional phrases in medical free texts. We use a small number of semantic interpretation schemata only, which operate on well-defined configurations in dependency graphs. We provide a quantitative analysis of the performance of the semantic interpreter in terms of recall/precision data, and consider, in qualitative terms, the impact semantic interpretation patterns have on the construction of the underlying medical ontology.

Humans↗

PubMed2001

Mapping the UMLS Semantic Network into general ontologies.

In this study, we analyzed the compatibility between an ontology of the biomedical domain (the UMLS Semantic Network) and two other ontologies: the Upper Cyc Ontology (UCO) and WordNet. 1) We manually mapped UMLS Semantic Types to UCO. One fifth of the UMLS Semantic Types had exact mapping to UCO types. UCO provides generic concepts and a structure that relies on a larger number of categories, despite its lack of depth in the biomedical domain. 2) We compared semantic classes in the UMLS and WordNet. 2% of the UMLS concepts from the Health Disorder class were present in WordNet, and compatibility between classes was 48%. WordNet, as a general language-oriented ontology is a source of lay knowledge, particularly important for consumer health applications.

Animals↗

PubMedDate not supplied

Behavioral and electrical brain measures of semantic priming in patients with Alzheimer's disease: implications for access failure versus deterioration hypotheses.

This study investigated the nature of anomia and semantic memory deficits in patients with Alzheimer's disease (DAT). We measured reaction time (RT) and the N400 event-related brain potential (ERP) in a word-picture semantic priming paradigm for DAT patients and elderly controls. For patients, pictures were classified as a function of the individual's naming ability to determine whether naming deficits reflected a failure to access a picture's name or reflected a deterioration of its semantic representation. As expected, DAT patients had significantly poorer naming performance than controls. For successfully named pictures, robust RT and ERP priming effects were obtained in both groups. In DAT patients, priming for unnamed pictures was heterogeneous. The results are discussed in terms of current hypotheses of semantic memory deficits in DAT.

Aged↗

PubMed1975

[Acoustic and semantic disturbances of comprehension in aphasia].

The authors carried out a verbal auditory comprehension test on 115 aphasic patients, 44 patients suffering from a left hemispheric lesion without aphasia and 120 normal subjects used as acontrol group. The test also revealed either disorders in acoustico-phonemic discrimination or difficulities in semantic differentiation. The main aim of the research was to check experimentally the theory propounded by Alajouanine and colleagues (1964) according to which, in Wernicke's aphasia, it is possible to demonstrate a twofold correlation between disorders of comprehension and speech disorders both phonemic and semantic. Only one part of the theory of Alajouanine and colleagues has been confirmed by our experiments for our results have shown that there is a very close correlation between semantic paraphasias and disorders of semantic differentiation whilst no correlation can be found between phonemic paraphasias and disturbances in auditory phonemic discrimination.

Aphasia↗

PubMed1992

The semantic structure of the UMLS Metathesaurus.

Meta-1.1, the UMLS metathesaurus, represents medical knowledge in the forms of names of concepts and links between those concepts. The representations of the semantic neighborhood of a concept can be thought of as dimensions of the property of semantic locality and include term information (broader, narrower, or otherwise related), the contextual information (parent-child, siblings in a hierarchy), the semantic types, and the co-occurrence data (links discovered empirically from concepts used to index the medical literature.) The degree of redundancy of each of these dimensions was investigated by reviewing the extent of multiple presentations of concepts which appear as related to a given concept. The degree of overlap was surprisingly small. While the co-occurrence data finds some of the links represented by other dimensions, those links are but minute fractions of the vast amount of co-occurrence derived links. Because parent-child relationships are often subsumptive (or categorical) in nature, it might be expected that siblings usually share the same semantic types. While true in the aggregate, the wide variance in percent of types shared may reflect the intended usages of the source vocabularies. Noun phrases were extracted from the definitions of 40 concepts in Meta-1 in order to assess systematically the coverage of important concepts by Meta-1, and to assess whether the links between these definitional concepts, which may have special value, and the concept being defined were indeed present. Out of 161 of these definitional concepts, 29 were not represented in Meta-1, and 37 of those represented in Meta-1 had no direct link to the concept they were defining.(ABSTRACT TRUNCATED AT 250 WORDS)

Semantics↗

PubMedDate not supplied

[Picture naming and memory in children: phonological and semantic effects].

BACKGROUND: [corrected] The relation between picture naming and the short and long term memories. AIM: to verify the ability of picture naming based on phonological and semantic queues, relating it to memory. METHOD: 80 pictures selected from a set of 400 (Cycowicz et al., 1997) were presented to 80 children with ages ranging from 3 to 6 years. Responses were classified in semantic and phonologic errors and number of correct answers. RESULTS: The effect of the articulatory complexity was significant and the effect of the semantic complexity was not significant. CONCLUSION: Naming is the result of memory activation which is organized in categories, physical properties and function; phonologic effects do interfere in the activity of naming, whereas the semantic effects reflect that the long term memory is organized in categories which are dependant of the context and of the development.

Child↗

PubMed2004

How vegetative is the vegetative state? Preserved semantic processing in VS patients--evidence from N 400 event-related potentials.

Event-related potentials (ERPs) can provide valuable information about cognitive capabilities in severely brain-damaged patients. This study examined 120 patients with severe brain damage using event related potentials ERPs (N 400) to gain information about their remaining semantic processing capabilities and to contribute to differential diagnosis. Patients were classified into three diagnostic groups: patients in vegetative state (VS), patients in near vegetative state (NEVS) and patients not in vegetative state (NOVS). N400 ERPs were analyzed on an individual basis. All three groups could be differentiated by N400. While VS-patients as a group were least likely to show N400, some VS-patients (approx. 12%) showed clear semantic N400 potentials as an indication of semantic processing capabilities. Patients in NEVS showed significantly more intact semantic capabilities (76.74%) than the VS-group despite little clinical differences between the two groups. Thus, ERPs provide valuable information about patients with brain injury whose clinical conditions often do not allow a true assessment of their cognitive capabilities. Given these findings, we would espouse that both ethical and legal debate should take into account results of ERP studies of such patients.

Adult↗

PubMedDate not supplied

[Brain mechanisms of the semantic analysis of words-homonyms].

The brain mechanisms of semantic comprehension of a word were comparatively studied in three experimental conditions: simple perception of the nuclear value of a word-homonym determined by the preceding context, perception of its circumferential value, and during active semantic analysis of these values. It was shown that the amplitude of the evoked potential component P200 was correlated with complexity of the semantic analysis. A decrease in this amplitude under conditions of complication of semantic problem was associated with an increase in the activities of the caudate nucleus and hippocampus and a parallel slight decrease in the activity of cortical areas.

Brain↗

PubMedDate not supplied

[Semantic dementia, a many-worded disorder].

INTRODUCTION: Semantic dementia is a progressive, relatively selective disorder affecting the semantic system with involvement of the verbal and non-verbal functions. The clinical picture is well characterised despite the confusion that may be generated by the different ways of classifying it. AIM. To determine the clinical, neurolinguistic, imaging and pathological features of this progressive language disorder. DEVELOPMENT: Evaluation of language reveals above all the existence of semantic paraphasias, disorders affecting the comprehension of isolated words and surface dyslexia. Flow of speech, complex syntactic comprehension and grammar are preserved. Both episodic and autobiographic memory are close to normality. Both the clinical signs and symptoms and imaging studies agree on the fact that the most heavily affected area is the anteroinferomedial region of the temporal lobe on a bilateral scale but with predominance of the left-hand side. Pathologically, in most cases positive intraneuronal ubiquitin inclusions are observed like those described in motor neuron diseases. CONCLUSIONS: Semantic dementia constitutes a diagnosis challenge, mainly from the neuropsychological point of view. Further advances towards reaching a diagnosis would allow us to determine which area is mainly affected and, in the future, to find an effective treatment for this progressive, degenerative disorder.

Aged↗

PubMedDate not supplied

Semantic standards for the representation of medical records.

Physicians developed their sublanguage (a system to represent medical concepts and their relations) to store and transmit general medical knowledge and patient-related information. Adequate formalisms are needed to obtain a standard representation of semantics of medical expressions for computer use. Comparison of the semantic contents of two expressions is possible only if a unique canonical form is defined; the transmission of medical facts or patient-related information is really meaningful only by defining a set of primitives (semantic categories and links) and the domains of values (concepts). These primitives must be harmonized to yield a "common core subset" of semantic categories and links. This subset provides a common basis; a procedure to register extension sets of primitives must also be defined, to comply with specific representation needs of specialties and classes of application software.

Artificial Intelligence↗

PubMed1991

A computational model of semantic memory impairment: modality specificity and emergent category specificity.

It is demonstrated how a modality-specific semantic memory system can account for category-specific impairments after brain damage. In Experiment 1, the hypothesis that visual and functional knowledge play different roles in the representation of living things and nonliving things is tested and confirmed. A parallel distributed processing model of semantic memory in which knowledge is subdivided by modality into visual and functional components is described. In Experiment 2, the model is lesioned, and it is confirmed that damage to visual semantics primarily impairs knowledge of living things, and damage to functional semantics primarily impairs knowledge of nonliving things. In Experiment 3, it is demonstrated that the model accounts naturally for a finding that had appeared problematic for a modality-specific architecture, namely, impaired retrieval of functional knowledge about living things. Finally, in Experiment 4, it is shown how the model can account for a recent observation of impaired knowledge of living things only when knowledge is probed verbally.

Amnesia↗

PubMed1990

[Event-related brain potentials reflect semantic and syntactic errors during language processing].

Event-related potentials were recorded in a sentence reading paradigm. Sentences were either terminated by a semantically and grammatically appropriate word (word from a different grammatical class syntactic error), a semantically inappropriate word (semantic error) or a semantically appropriate word with a wrong case inflection (morphosyntactic error). For all three types of errors the event-related potential was characterized by a negativity in the 250-600 ms range (N400). The possible implications of these findings for models of sentence processing are discussed. It is concluded that the results strongly support interactive models of sentence processing.

Adult↗