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PubMed2005

Semantic feature knowledge and picture naming in dementia of Alzheimer's type: a new approach.

This study addresses continuing controversies concerning the nature of semantic impairment in early dementia of the Alzheimer type (DAT), and the relationship between conceptual knowledge and picture naming. A series of analyses of fine-grained feature knowledge data show that: (1) distinctive features of concepts were more vulnerable than shared; (2) the amount of attribute knowledge about a concept was associated reliably, and in a graded fashion, with the ability to name a picture of that item; (3) sensory features were differentially important in naming; and (4) the degree of disruption to different types of attribute knowledge did not vary between items from living and nonliving domains. These findings are discussed in the context of contemporary cognitive and computational models of semantic memory organisation.

Aged↗

PubMed2005

Impairment of syntax and lexical semantics in a patient with bilateral paramedian thalamic infarction.

Bilateral vascular thalamic lesions are rare. Although a variety of neurobehavioral manifestations have been described, the literature is less documented with regard to accompanying linguistic disturbances. This article presents an in-depth neurolinguistic analysis of the language symptoms of a patient who incurred bilateral paramedian ischemic damage of the thalamus. In the post-acute phase of the stroke, a unique combination of transcortical sensory aphasia with syntactic impairment was found. Because of this atypical semiological association, additional analyses of spontaneous speech were performed. In spite of the typological affinity with the grammatic characteristic of marked simplification of syntax observed in Broca's aphasia, only a wordclass specific, lexical-semantic deficit for verbs was objectified. The hypothesis that lexical-semantic disturbances in our patient might result from a functional deafferentiation of both thalami with the frontal lobe is supported by: (1) associated neuropsychological deficits of frontal origin and (2) frontal-like behavioral disturbances.

Aged↗

PubMed2006

ERPs and contextual semantic discrimination: degrees of congruence in wakefulness and sleep.

This study explores whether the brain can discriminate degrees of semantic congruency during wakefulness and sleep. Experiment 1 was conducted during wakefulness to test degrees of congruency by means of N400 amplitude. In Experiment 2, the same paradigm was applied to a different group of participants during natural night sleep. Stimuli were 108 sentences (definitions with two attributes) with four possible degrees of congruence as ending targets. In both studies, the amplitude of N400-like effect showed modulation according to the degree of congruency. The results indicate that the brain can accomplish sentential semantic discriminations not only in wakefulness but also in sleep.

Acoustic Stimulation↗

PubMed2003

Semantic decision making in early probable AD: a PET activation study.

We studied the neural correlates of semantic decision making in early probable Alzheimer disease patients and age-matched controls by measuring changes in relative cerebral blood flow by PET (oxygen-15) while they performed a category-specific word-matching task with either animal or artefact names. In comparison to a baseline (matching words by physical identity), semantic decision making elicited increased blood flow in the left frontal lobe (BA 6, 11, 47) and in the contralateral cerebellum in the controls. The only category-specific difference in controls was activation of the left supplementary motor area (BA 6) when making decisions on artefacts. In contrast, the patients recruited more extensive brain regions, encompassing areas in the left frontal lobe (BA 44, 45, 47), right occipital cortex (BA 18), midbrain, and the cerebellum bilaterally. Behaviorally, the patients performed the tasks with equal success albeit more slowly. No animal-artefact differences emerged in the patients' activation patterns, indicating that their activation increases reflected a generalized, presumably compensatory reaction to higher task demands in the face of a progressive neurological disease.

Aged↗

PubMed2004

Hemispheric asymmetry for spatially filtered stimuli belonging to different semantic categories.

The hemispheric specialization for processing visual stimuli as a function of spatial-frequency content and semantic category was investigated. Spatially filtered pictures of animals and tools were displayed to both hemifields at nine levels of spatial-frequency filtering following a coarse-to-fine design. Results showed a differential hemispheric specialization in relation to the semantic category of stimuli. Animals might be identified at low spatial frequencies (coarse information) in a similar extent in both hemifield conditions, while a hemispheric dissociation was found for tools (the increasing of levels of high-spatial frequency information was especially needed when such stimuli were presented to the left visual field /right hemisphere (RH) relative to that for right visual field/left hemisphere presentations).

Adult↗

PubMed2005

Neural impact of the semantic content of visual mental images and visual percepts.

The existence of hemispheric lateralization of visual mental imagery remains controversial. In light of the literature, we used fMRI to test whether processing of mental images of object drawings preferentially engages the left hemisphere to compared non-object drawings. An equivalent comparison was also made while participants actually perceived object and non-object drawings. Although these two conditions engaged both hemispheres, activation was significantly stronger in the left occipito-temporo-frontal network during mental inspection of object than of non-object drawings. This network was also activated when perception of object drawings was compared to that of non-object drawings. An interaction was nonetheless observed: this effect was stronger during imagery than during perception in the left inferior frontal and the left inferior temporal gyrus. Although the tasks subjects performed did not explicitly require semantic analysis, activation of this network probably reflected, at least in part, a semantic and possibly a verbal retrieval component when object drawings were processed. Mental imagery tasks elicited activation of early visual cortex at a lower level than perception tasks. In the context of the imagery debate, these findings indicate that, as previously suggested, figurative imagery could involve primary visual cortex and adjacent areas.

Adolescent↗

PubMed2005

The recognition potential: semantic processing or the detection of differences between stimuli?

The recognition potential is traditionally described as an electrical index elicited when subjects view a recognizable stimulus. Recent studies further show that it may be influenced by semantic processing. In this study, we investigated whether this observed influence is really produced by differences in semantic processing or whether it might be caused by the detection of differences between sequentially presented stimuli. In two different experiments, we systematically altered the type of background images presented while keeping the recognizable word constant. Analyses revealed that the same recognizable words elicited an RP with different amplitudes and latencies when viewed under different background conditions. Control stimuli, which were identical to background stimuli, did not elicit the RP. Hence, we postulate that when using the rapid stream stimulation paradigm, RP might also be influenced by the detection of differences between sequentially input stimuli. It is necessary to clarify whether RP changes are caused by the processing of the stimuli or by the detection of difference between successively input stimuli before any conclusion could be made.

Adult↗

PubMed2004

Different time courses of integrative semantic processing for plural and singular nouns: implications for theories of sentence processing.

The research investigated the time course of integrative semantic processing during sentence processing. Reading time was measured on sentences containing an NP composed of an adjective and a noun whose combined meaning was plausible or anomalous (Experiment 1) or was typical or atypical (Experiment 2). The noun in the NP was either plural or singular. Plural nouns were expected to be more rapidly integrated with a preceding adjective than singular nouns because plural nouns can be ruled out as the first noun in a noun compound more rapidly than singular nouns. The results confirmed this prediction, showing that the effects of semantic plausibility and typicality were observed immediately during the processing of plural nouns, but were observed at a delay following the processing of singular nouns. Implications for theories of sentence processing are discussed.

Adult↗

PubMed2005

Semantic evaluation of syntactic structure: evidence from eye movements.

An eye movement study of temporarily ambiguous closure sentences confirmed that the early closure penalty in a sentence like While John hunted the frightened deer escaped is larger for a simple past verb (hunted) than for a past progressive verb (was hunting). The results can be explained by the observation that simple past tense verbs convey an external viewpoint on an event, which presumably fits best when the event described has an endpoint. A definite description object supplies an endpoint. Consequently, to give up the late closure analysis of the post-verbal object when the verb is in the simple past tense, the processor is abandoning an analysis with semantically-expected properties for one which is not as good semantically. By contrast, a progressive verb denotes an activity which does not require an endpoint and therefore is neutral with respect to whether or not it takes an object.

Eye Movements↗

PubMed2006

The influence of intention on masked priming: a study with semantic classification of words.

Unconscious perception is commonly described as a phenomenon that is not under intentional control and relies on automatic processes. We challenge this view by arguing that some automatic processes may indeed be under intentional control, which is implemented in task-sets that define how the task is to be performed. In consequence, those prime attributes that are relevant to the task will be most effective. To investigate this hypothesis, we used a paradigm which has been shown to yield reliable short-lived priming in tasks based on semantic classification of words. This type of study uses fast, well practised classification responses, whereby responses to targets are much less accurate if prime and target belong to a different category than if they belong to the same category. In three experiments, we investigated whether the intention to classify the same words with respect to different semantic categories had a differential effect on priming. The results suggest that this was indeed the case: Priming varied with the task in all experiments. However, although participants reported not seeing the primes, they were able to classify the primes better than chance using the classification task they had used before with the targets. When a lexical task was used for discrimination in experiment 4, masked primes could however not be discriminated. Also, priming was as pronounced when the primes were visible as when they were invisible. The pattern of results suggests that participants had intentional control on prime processing, even if they reported not seeing the primes.

Decision Making↗

PubMed2006

Semantic re-interpretation and garden path recovery.

Participant's eye-movements were recorded while they read locally ambiguous sentences. Evidence for processing difficulty was found when the interpretation of the initially preferred misanalysis clashed with that of the globally correct analysis, demonstrating the persistence of the earlier interpretation. Processing difficulty associated with the syntactic reanalysis was largely localised to the disambiguating region, with difficulty due to semantic persistence occurring later. The results show that semantic persistence is not limited to extreme cases of parse failure, and can occur even when reanalysis is relatively straightforward.

Attention↗

PubMed2004

Semantic integration and syntactic planning in language production.

Five experiments, using a subject-verb agreement error elicitation procedure, investigated syntactic planning processes in production. The experiments examined the influence of semantic integration--the degree to which phrases are tightly linked at the conceptual level--and contrasted two accounts of planning: serial stack-based systems and parallel activation-based systems. Serial stack-based systems rely on memory-shifting processes to coordinate ongoing planning. Memory-shifting should be easier for more integrated phrases, resulting in fewer errors. Parallel, activation-based systems, on the other hand, maintain multiple representations simultaneously in memory. More integrated phrases will be more likely to be processed together, resulting in increased interference and more errors. Participants completed stimuli like The drawing of/with the flower(s), which varied local noun number (flower(s)) and the relationship between the head (drawing) and local noun. In some constructions, the nouns were tightly integrated (e.g., of), whereas in others the relationship was looser (e.g., with, specifying accompaniment). In addition to the well-established local noun mismatch effect (more errors for plural than for singular local nouns), all experiments revealed larger mismatch error effects following tightly integrated stimuli. These results are compatible with parallel activation-based accounts and cannot be explained by serial, memory-shift-based accounts. The experiments and three meta-analyses also ruled out alternative accounts based on plausibility, argumenthood, conceptual number, clause packaging, or hierarchical feature-passing, reinforcing the general finding that error rates increase with degree of semantic integration.

Humans↗

PubMed2006

Unconscious semantic priming in the absence of partial awareness.

In a recent paper in Psychological Science, Kouider and Dupoux reported obtaining unconscious Stroop priming only when subjects had partial awareness of the masked distractor words (i.e., could consciously perceive subword features that enabled reconstruction of whole words). Kouider and Dupoux conjectured that semantic priming occurs only when such partial awareness is present. The present experiments tested this conjecture in an affective categorization priming task that differed from Kouider and Dupoux's in using masked distractors that subjects had practiced earlier as visible words. Experiment 1 showed priming from practiced words when subjects had no partial awareness of those words. Experiment 2 showed that, in the absence of partial awareness, practiced words yielded priming but not-practiced words did not. Experiment 3 corroborated Experiment 1 and 2s results using a different test of partial awareness. These results suggest that unconscious processing (rather than partial awareness) of subword elements drives masked semantic priming by practiced words.

Affect↗

PubMed2005

Genome semantics, in silico multicellular systems and the Central Dogma.

Genomes with their complexity and size present what appears to be an impossible challenge. Scientists speak in terms of decades or even centuries before we will understand how genomes and their hosts the cell and the city of cells that make up the multicellular context function. We believe that there will be surprisingly quick progress made in our understanding of genomes. The key is to stop taking the Central Dogma as the only direction in which genome research can scale the semantics of genomes. Instead a top-down approach coupled with a bottom-up approach may snare the unwieldy beast and make sense of genomes. The method we propose is to take in silico biology seriously. By developing in silico models of genomes cells and multicellular systems, we position ourselves to develop a theory of meaning for artificial genomes. Then using that develop a natural semantics of genomes.

Cells↗

PubMed2004

A multi-layered application for the gross description using Semantic Web technology.

OBJECTIVE: Development of a Semantic Web technology based system for the formalization of the gross description. METHOD: A system is developed using the Java-2 platform. It is based on a light-weight version of the Galen top level ontology. Web technologies like XML, SAX en DOM have been used. RESULT: Three system components have been developed to support the semantic, the object and the syntax layers of the PathOnt architecture. CONCLUSION: The PathOnt approach provides a tool for the communication among clinicians and technicians involved in pathology examinations. This tool also provides a foundation for linking the specimen-specific data with the controlled medical ontology so that the stored information can be used in different circumstances.

Internet↗

PubMed2003

Designing metaschemas for the UMLS enriched semantic network.

The enriched semantic network (ESN) has previously been presented as an enhancement of the semantic network (SN) of the UMLS. The ESN's hierarchy is a DAG (Directed Acyclic Graph) structure allowing for multiple parents. The ESN is thus more complex than the SN and can be more difficult to view and comprehend. We have previously introduced the notion of a metaschema for the SN as a compact abstraction to support SN comprehension. We extend the definition of metaschema to make it applicable to a DAG classification hierarchy, such as the one exhibited by the ESN. We specify the requirements for and describe the general process of deriving such a metaschema. We derive two particular metaschemas of the ESN based on a pair of partitions. These two metaschemas and their underlying partitions are compared. Both metaschemas serve as compact representations of the ESN, allowing for convenient viewing of its hierarchy and easier comprehension.

Abstracting and Indexing↗

PubMed2005

Graph theoretic modeling of large-scale semantic networks.

During the past several years, social network analysis methods have been used to model many complex real-world phenomena, including social networks, transportation networks, and the Internet. Graph theoretic methods, based on an elegant representation of entities and relationships, have been used in computational biology to study biological networks; however they have not yet been adopted widely by the greater informatics community. The graphs produced are generally large, sparse, and complex, and share common global topological properties. In this review of research (1998-2005) on large-scale semantic networks, we used a tailored search strategy to identify articles involving both a graph theoretic perspective and semantic information. Thirty-one relevant articles were retrieved. The majority (28, 90.3%) involved an investigation of a real-world network. These included corpora, thesauri, dictionaries, large computer programs, biological neuronal networks, word association networks, and files on the Internet. Twenty-two of the 28 (78.6%) involved a graph comprised of words or phrases. Fifteen of the 28 (53.6%) mentioned evidence of small-world characteristics in the network investigated. Eleven (39.3%) reported a scale-free topology, which tends to have a similar appearance when examined at varying scales. The results of this review indicate that networks generated from natural language have topological properties common to other natural phenomena. It has not yet been determined whether artificial human-curated terminology systems in biomedicine share these properties. Large network analysis methods have potential application in a variety of areas of informatics, such as in development of controlled vocabularies and for characterizing a given domain.

Algorithms↗

PubMed2006

Measures of semantic similarity and relatedness in the biomedical domain.

Measures of semantic similarity between concepts are widely used in Natural Language Processing. In this article, we show how six existing domain-independent measures can be adapted to the biomedical domain. These measures were originally based on WordNet, an English lexical database of concepts and relations. In this research, we adapt these measures to the SNOMED-CT ontology of medical concepts. The measures include two path-based measures, and three measures that augment path-based measures with information content statistics from corpora. We also derive a context vector measure based on medical corpora that can be used as a measure of semantic relatedness. These six measures are evaluated against a newly created test bed of 30 medical concept pairs scored by three physicians and nine medical coders. We find that the medical coders and physicians differ in their ratings, and that the context vector measure correlates most closely with the physicians, while the path-based measures and one of the information content measures correlates most closely with the medical coders. We conclude that there is a role both for more flexible measures of relatedness based on information derived from corpora, as well as for measures that rely on existing ontological structures.

Database Management Systems↗