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PubMed2001

Characterizing semantic space: neighborhood effects in word recognition.

A specification of the structural characteristics of the mental lexicon is a central goal in word recognition research. Of various word-level characteristics, semantics remains the most resistant to this endeavor. Although there are several theoretically distinct models of lexical semantics with fairly clear operational definitions (e.g., in terms of feature sharing, category membership, associations, or cooccurrences), attempts to empirically adjudicate between these different models have been scarce. In this paper, we present several experiments in which we examined the effects of semantic neighborhood size as defined by two models of lexical semantics--one that defines semantics in terms of associations, and another that defines it in terms of global co-occurrences. We present data that address the question of whether these measures can be fruitfully applied to examinations of lexical activation during visual word recognition. The findings demonstrate that semantic neighborhood can predict perforrmance on both lexical decision and word naming.

Adult↗

PubMed2003

Locus of semantic interference in picture-word interference tasks.

Picture-word interference studies typically show that semantically related distractor words embedded within a picture slow picture-naming responses, relative to unrelated ones. This semantic interference effect is commonly interpreted as arising from the competition of lexical-semantic (e.g., Schriefers, Meyer, & Levelt, 1990) or lexical-phonological (e.g., Starreveld & La Heij, 1996) codes. The experiment reported here tests a crucial assumption shared by these accounts--namely, that the effect reflects a lexical, rather than a nonverbal, conceptual conflict. Pictures were named while participants attempted to ignore embedded distractors that were in either verbal or pictorial format. The presence of both words and pictures substantially interfered with naming responses, but only words, not pictures, were found to induce semantic interference. These findings support the claim that for semantic interference to arise, both target picture and distractor have to be lexicalized. Consequently, a general conceptual locus of the effect can be excluded, and the claim that semantic interference is based on a lexical conflict is confirmed.

Adolescent↗

PubMed2003

Beyond spreading activation: an influence of relatedness proportion on masked semantic priming.

Semantic priming in the lexical decision task has been shown to increase when the proportion of related-prime trials is increased. This finding typically is taken as evidence for a conscious, strategic use of primes. Three experiments are reported in which masked semantic primes displayed for only 45 msec were tested in high- versus low-relatedness proportion conditions. Relatedness proportion was increased either by using a high proportion of semantically related primes or a large set of repetition-primed filler trials. Semantic priming was consistently enhanced relative to a low-relatedness proportion condition. These relatedness proportion effects were not due to conscious, strategic use of primes: Exclusion of prime-aware subjects did not attenuate the effects, and better performance in a prime classification task was not associated with larger semantic priming effects. These results are interpreted within a retrospective account of semantic priming in which recruitment of a prime event is modulated by prime validity.

Awareness↗

PubMed2004

The effect of semantic ambiguity on reading aloud: a twist in the tale.

Despite numerous studies investigating whether semantic representations are involved in the process of reading aloud, the issue remains controversial. While some studies report significant effects of semantic variables on this task (e.g., Fera, Joordens, Balota, Ferraro, & Besner, 1992; Strain, Patterson, & Seidenberg, 1995), other studies have highlighted possible problems with these studies (e.g., Borowsky & Masson, 1996; Monaghan & Ellis, 2002). The experiments reported here use semantic ambiguity as a marker for semantic involvement and confirm that semantic representations can indeed affect reading aloud, but that the size of semantic effects is influenced by the consistency of the words and the speed with which participants respond.

Humans↗

PubMed1995

Processing relative clauses varying on syntactic and semantic dimensions: an analysis with event-related potentials.

Event-related potentials were used to study how parsing of German relative clauses is influenced by semantic information. Subjects read well-formed sentences containing either a subject or an object relative clause and answered questions concerning the thematic roles expressed in those sentences. Half of the sentences contained past participles that on grounds of semantic plausibility biased either a subject or an object relative reading; the other half contained past participles that provided no semantic information favoring either reading. The past participle elicited an N400 component, larger in amplitude for neutral than for semantically biased verbs, but this occurred only in the case of subject relative clauses. More specific effects were obtained only for a subgroup of subjects, when these were grouped into fast and slow comprehenders on the basis of their question-answering reaction times. Fast comprehenders showed larger N400 amplitudes for neutral than for semantically biased past participles in general and larger N400s for the latter when there was a bias for an object relative reading as opposed to a subject relative reading. Syntactic ambiguity resolution, indicated by an auxiliary in sentence final position, was associated in this subgroup with a positive component (P345), larger in amplitude for auxiliaries indicating an object relative reading than for those indicating a subject relative reading. The latter component was independent of semantically biasing information given by a preceding past participle. Implications of these findings for models of language comprehension are considered.

Adult↗

PubMed1997

The effect of presemantic acoustic adaptation on semantic "satiation".

A decrement in the strength of the meaning of a word after rapid repetition of that word has been called "semantic satiation." This study asked whether this "satiation" might be produced by presemantic acoustic adaptation. Category words were utilized to prime the meaning of target words. The adaptation or "satiation" procedure, 30 rapid repetitions of the primes, was compared with a control condition of 3 repetitions. Participants listened to a series of prime words, each repeated by either the same speaker or many speakers, and then made semantic decisions on target words. When all the repetitions of a prime word are produced by the same speaker, presemantic and semantic repetitions are confounded. When the repetitions are produced by different speakers, presemantic acoustic repetition is abolished. A semantic decrement was detected with single-speaker, but not with multiple-speaker, repetitions of prime words. This study concluded that the semantic "satiation" observed here was a decrement in the activation level of semantic representations induced by presemantic acoustic adaptation.

Analysis of Variance↗

PubMed2000

On the locus of the semantic satiation effect: evidence from event-related brain potentials.

The present study sought to determine whether semantic satiation is merely a by-product of adaptation or satiation of upstream, nonsemantic perceptual processes or whether the effect can have a locus in semantic memory. This was done by measuring event-related brain potentials (ERPs) in a semantic word-detection task involving multiple presentations of primes and critical related and unrelated words in three experiments involving visual (Experiment 1) and auditory (Experiments 2A and 2B) stimuli. Primes varied in their type case (Experiment 1) or pitch (Experiment 2B) in order to discourage sensory adaptation. Prime satiation and relatedness of the primes to the critical word had interacting effects on ERP amplitude to critical words, particularly within the time-window of the N400 component. Because numerous studies have indicated a role for the N400 in semantic processing, modulation of the N400 relatedness effect by prime satiation (with little or no contribution from perceptual adaptation) suggests that semantic memory can be directly satiated, rather than the cost to semantic processing necessarily resulting from impoverishment of perceptual inputs.

Adult↗

PubMed2002

The impact of synaptic depression following brain damage: a connectionist account of "access/refractory" and "degraded-store" semantic impairments.

Neuropsychological studies of patients with acquired semantic impairments have yielded two distinct and contrasting patterns of performance in a spoken-word/picture-matching task (Warrington & Cipolotti, 1996). Patients labeled access/refractory are strongly influenced by presentation rate, semantic relatedness of distractors, and repetition, yet they seem relatively unaffected by lexical frequency. Degraded-store patients, on the other hand, are strongly affected by lexical frequency but are less affected by presentation rate, semantic relatedness, or repetition. Our account of these patterns of performance is based on the distinction between two different types of neurological damage: (1) damage to neuromodulatory systems that function to amplify neural signals while suppressing normal refractory-like effects and (2) damage to connections between groups of neurons that encode semantic information and are sensitive to frequency/familiarity. We present a connectionist model that learns to map spoken-word input to semantic representations and that incorporates a particular form of neural refractoriness referred to as synaptic depression, as well as a simple form of neuromodulation. We show that the model is capable of accounting for the contrasting patterns of semantic impairment under these two different forms of damage and, furthermore, demonstrate how it is capable of handling several documented cases that are exceptions to the basic patterns of impairment. Several predictions and limitations of the present model are discussed.

Brain Damage, Chronic↗

PubMed2004

When does word meaning affect immediate serial recall in semantic dementia?

Patients with semantic dementia can show superior immediate recall of words that they still understand relatively well, as compared with more semantically degraded words, suggesting that conceptual knowledge makes a major contribution to phonological short-term memory. However, a number of studies have failed to show such a recall difference, challenging this view. We examined the effect of several methodological factors on the recall of known and degraded words in 4 patients with semantic dementia, in order to investigate possible reasons for this discrepancy. In general, our patients did exhibit poorer recall of the degraded words and made more phonological errors on these items. In addition, set size affected the magnitude of the recall advantage for known words. This finding suggests that semantic degradation influenced the rate of learning in the immediate recall task when the same items were presented repeatedly. The methods used to select known and degraded items also impacted on the recall difference. List length, however, did not affect the advantage for known words. The coherence of items in phonological short-term memory was affected by their semantic status, but not by the length of the material to be retained. The implications of these findings for the role of semantic and phonological representations in verbal short-term memory are discussed.

Aged↗

PubMed2001

An object-oriented model for representing semantic locality in the UMLS.

Several information models have been developed for the Unified Medical Language System (UMLS). While some models are term-oriented, a knowledge-oriented model is needed for representing semantic locality, i.e. the various semantic links among concepts. We propose an object-oriented model in which the semantic features of the UMLS are made available through four major classes for representing Metathesaurus concepts, semantic types, inter-concept relationships and Semantic Network relationships. Additional semantic methods for reducing the complexity of the hierarchical relationships represented in the UMLS are proposed. Implementation details are presented, as well as examples of use. The interest of this approach is discussed.

Artificial Intelligence↗

PubMed2001

Expression and meaning of medical language: building an epistemological framework for the study of semantic distance.

The use of language for communication purposes introduces a semantic gap in data processing. We have developed a new tool called semantic distance to overcome this gap. A previous presentation of our tool was based on an empirical approach. Here, we examine the properties and theoretical foundation of semantic distance from a rationalistic perspective. We present an epistemological framework to explain the meaning of semantic distance. As a tool, the purpose of semantic distance is the exchange of data or knowledge based on linguistic expressions between software components. We propose a review of the relationship between language and its representation for data processing based on the underlying philosophical assumptions. Description logic is a new paradigm in the medical informatics community to express relations between terms in "is-a" hierarchies. The utility of semantic distance is compared to description logic for communication purposes in different use cases.

Knowledge↗

PubMed2002

Evidence for intact semantic representations in patients with frontal lobe lesions.

Patients with frontal lobe lesions and control participants were assessed on 2 tests of semantic knowledge. In the triadic comparison task, participants were shown all possible triplets of 12 animal names and judged which 2 of each triplet were most alike. In the ordered similarity task, participants rank ordered animals in terms of their similarity to a target animal. For both tasks, semantic structure--derived from multidimensional scaling techniques--revealed similar representations in patients with frontal lobe lesions and control participants. Additional pathfinder analyses also produced networks that did not differ between groups. These patients exhibited intact semantic knowledge despite deficits on tests of free recall and verbal fluency that involved the same semantic category and exemplars. Thus, intact representation of semantic knowledge in frontal patients stands in contrast to their marked deficits in strategic retrieval of semantic knowledge.

Adult↗

PubMed2002

Picture naming by children with hearing loss: I. Effect of semantically related auditory distractors.

Thirty children with hearing loss (HL) and 129 typically developing (TD) children representing comparable ages, vocabulary ability, or phonology skills named pictures while attempting to ignore semantically related or unrelated auditory distractors. The timing relation between the onsets of the distractors and pictures varied. A significant semantic interference effect, that is, slowed naming in the presence of the semantically related distractor, was observed in all groups, suggesting similar categorical knowledge in the HL and TD groups. The time course of semantic interference, however, was protracted in some children with HL, primarily those with unusually slow baseline naming speeds and early ages of identification/amplification of the loss. Thus, children with HL seem to develop normal lexical semantic representations. At the same time, the dynamics of semantic processing appear to be altered by the presence of early childhood HL.

Adolescent↗

PubMed2004

A first look at HealthCyberMap medical semantic subject search engine.

HealthCyberMap (http://healthcybermap.semanticweb.org) is a Semantic Web project that aims at mapping selected parts of health information resources in cyberspace in novel semantic ways to improve their retrieval and navigation. This paper describes HealthCyberMap semantic subject search engine methodology and early prototype which attempt to overcome the limitations of conventional free text search engines. Explicit concepts in resource metadata map onto a brokering domain ontology (a clinical terminology or classification) allowing a Semantic Web search engine to infer implicit meanings (synonyms and semantic relationships) not directly mentioned in either the resource or its metadata. Similarly, user queries would map to the same ontology allowing the search engine to infer the implicit semantics of user queries and use them to optimise retrieval. Related issues of metadata, clinical terminologies and automatic vs. manual indexing of medical Web resources are also discussed, together with future methodological directions, which include the use of a true terminology server as an intelligent broker between user queries and HealthCyberMap pool of resource metadata. A comparative evaluation of the new engine based on relevance metrics is also proposed.

Humans↗

PubMed2004

A corpus driven approach applying the "frame semantic" method for modeling functional status terminology.

In an effort to unearth semantic models that could prove fruitful to functional-status terminology development we applied the "frame semantic" method, derived from the linguistic theory of thematic roles currently exemplified in the Berkeley "FrameNet" Project. Full descriptive sentences with functional-status conceptual meaning were derived from structured content within a corpus of questionnaire assessment instruments commonly used in clinical practice for functional-status assessment. Syntactic components in those sentences were delineated through manual annotation and mark-up. The annotated syntactic constituents were tagged as frame elements according to their semantic role within the context of the derived functional-status expression. Through this process generalizable "semantic frames" were elaborated with recurring "frame elements". The "frame semantic" method as an approach to rendering semantic models for functional-status terminology development and its use as a basis for machine recognition of functional status data in clinical narratives are discussed.

Information Science↗

PubMed1995

Associating semantic grammars with the SNOMED: processing medical language and representing clinical facts into a language-independent frame.

We describe one approach for natural language processing of medical texts that associates a semantic grammar with the SNOMED (Systematized Nomenclature of Medicine). Our research hypothesis is that the combination of the nomenclature's declarative knowledge with a formal grammar would create a scientific sublanguage embedded with medical knowledge that could be used for analyzing and formatting medical texts. This combination permitted the abstraction of templates we call "semantic patterns." These patterns represent both linguistic and medical knowledge, packed into a hybrid information format. We analyzed manually case reports described in the New England Journal of Medicine (NEJM) from 1985 to 1988 and extracted empirically a semantic grammar. Over 2,000 sentences were analyzed. About 160 structural semantic patterns were abstracted and included in the database of one parser. We tested the parser using reports from 1989 to 1990. Results show that this approach is efficient for processing, indexing, and structuring diverse parts of case reports narrative. The analyzed medical sentences are structured into a language-independent semantic frame format. We conclude that the association of semantic grammars with the SNOMED enabled the construction of a formal system for analysis and representation of clinical facts. The transformation of the structured information from its frame format into other representational schemes, like conceptual graphs, is straightforward. Another application includes the use of the formatted language-independent frame for telegraphic English-Japanese translations of medical sentences.

Language↗

PubMed1997

A comparison of semantic memory in vascular dementia and dementia of Alzheimer's type.

OBJECTIVE: To determine whether semantic memory is impaired in vascular dementia and to assess the utility of semantic memory measures in differentiating vascular dementia from dementia of Alzheimer's type (DAT). DESIGN: Case-control study. PATIENTS: Ten patients with Cambridge Mental Disorders in the Elderly (CAMDEX) diagnosis of 'definite' mild or moderate vascular dementia (mean age 77) were individually matched with 10 patients with a CAMDEX diagnosis of 'definite' DAT on the basis of age, education, sex, premorbid IQ (as measured by the National Adult Reading Test) and performance on the Cambridge Cognitive Examination (CAMCOG). In addition, 10 age, sex and education matched volunteer or relative controls were assessed. OUTCOME MEASURES: A detailed semantic memory test battery consisting of five subtests: category fluency, picture naming, picture sorting, word-picture matching and generation of verbal definitions. RESULTS: Compared to normal controls, both patient groups were impaired on all subtests of the semantic battery with the exception of the word-picture matching test. No differences were found between the vascular dementia and DAT groups on any of the measures. CONCLUSIONS: Impairment of semantic memory is a feature of both vascular dementia and DAT. Tests of semantic memory appear, therefore, of little value in differentiating between these two major causes of dementia. Further work is required to determine whether the nature of the processing deficit is the same in these conditions.

Aged↗

PubMed1995

Modulation of semantic processing using word length and complexity: an ERP study.

The objective of this study was to assess changes in semantic priming in two experiments which separately manipulated word length and the location of a semantic incongruence within spoken compound words. All words began 1500 ms after the presentation of related, partially unrelated, or totally unrelated picture-primes. Using a picture of a dogbone as an example, either the spoken words DOGBONE, WISHBONE, DOGHOUSE, or MAILBOX could occur as targets (underscores indicate semantically unrelated parts). In practice, only one of the four possible targets occurred with each prime. Subjects made speeded responses by pressing one of two buttons (related/unrelated) while event-related brain potentials (ERPs) were collected from various scalp locations. The behavioral analyses of response time and accuracy were sensitive to changes in word length, but inconclusive for semantic relatedness. However, repeated-measures ANOVAs of peak amplitude, latency, and mean area amplitude of the N400 ERP revealed significant effects of word length and semantic priming. Comparison of related compounds with partially unrelated word-initial violations of context (e.g., WISHBONE) revealed diminished activity following the peak of the N400. Comparison of partially unrelated word-final contextual violations (e.g., DOGHOUSE) revealed an N400 effect delayed by approximately the mean length of the word-initial component. These results demonstrate the dynamic sensitivity of the cortical semantic processor.

Adolescent↗