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PubMed2003

An ERP study of continuous speech processing. II. Segmentation, semantics, and syntax in non-native speakers.

Behavioral and electrophysiological studies indicate that altered language experience has different effects on distinct subsystems within language. In this study, we recorded event-related potentials (ERPs) in native Japanese late-learners of English listening to English sentences. ERP indices of semantic processing, syntactic processing, and speech segmentation were compared and contrasted for native Japanese and previously tested native English speakers. Native and non-native speakers showed similar semantic processing effects including an N400 for words as opposed to nonwords. In contrast, native Japanese speakers showed none of the effects associated with syntactic processing in native English speakers including an anterior negativity to nonwords presented in a syntactic context. Furthermore, the ERP word-onset effect evident in native English speakers was not found for the native Japanese speakers in this study. These data contribute additional and specific evidence to the proposal that subsystems within language display varying degrees of plasticity.

Adult↗

PubMed2003

Category-specific medial temporal lobe activation and the consolidation of semantic memory: evidence from fMRI.

Semantic memory consolidation was studied by comparing medial temporal lobe (MTL) fMRI activation to ANIMAL, IMPLEMENT and ABSTRACT nouns in healthy seniors to that of young adults. Relative to healthy seniors, young adults were predicted to show greater MTL activation for IMPLEMENTS, but not ANIMALS, because the ANIMALS category consists of highly intercorrelated and overlapping features that should require less MTL-mediated binding than IMPLEMENTS over a shorter period of time during concept consolidation. ABSTRACT meanings are context-dependent and do not consist of fixed feature sets. Thus it was predicted that ABSTRACT words would not involve age-related feature binding mediated by the MTL. These predictions were confirmed by the results. Our observations are consistent with the hypothesis that the structure of a category influences the consolidation of knowledge in semantic memory.

Adult↗

PubMed1996

Functional MR imaging of semantic information processing and learning-related effects using psychometrically controlled stimulation paradigms.

Functional magnetic resonance imaging (fMRI), in conjunction with carefully designed, psychometrically optimized stimulation procedures, was used to investigate the relation between brain activation and the processing of word associations. A semantic discrimination task of word-pair similarity was performed by normal subjects (n = 17) within a clinical 1.5-Tesla whole-body MRI system. A color similarity task of psychometrically equivalent difficulty, as indicated by behavioral data acquired online during fMRI, served as active control condition. Comparisons between tasks dramatically improved results compared to comparisons between task and resting condition. The language paradigm selectively activated left frontal and left fronto-temporal areas. Cortical activation during the semantic task decreased significantly over three runs of the same word list and was paralleled by decreased reaction times. No such changes were observed in the active control condition indicating selective learning of the language task only. When combined with psychological activation schemes and the acquisition of behavioral data, fMRI represents a powerful tool for the study of brain-behavior interaction.

Adult↗

PubMed1998

Event-related potential indices of semantic priming following an unrelated intervening item.

Interposing an unrelated word between related primes and targets often disrupts priming. This finding has been used to support the view that semantic information is represented in a distributed fashion, rather than locally. In some studies where unrelated items intervened between the prime and target, however, significant priming was nevertheless obtained. The discrepant results of these studies has been attributed to differences in speed-accuracy tradeoff, post-lexical checking, conscious rehearsal of the prime and differences in the depth to which the prime and target were processed. The present study was designed in such a way as to minimize variability associated with post-lexical influences. The N400 component of the human event-related potential was used as a physiological index of the extent to which priming occurred with and without the interposition of an unrelated item. Priming effects on both the amplitude and latency of the N400 were rendered non-significant by the presence of an intervening unrelated word. The results are interpreted as tentative evidence that semantic representations are distributed.

Adolescent↗

PubMed1998

Functional magnetic resonance imaging of category-specific cortical activation: evidence for semantic maps.

Functional magnetic resonance imaging (fMRI) was used to examine the pattern of cortical activity during a picture naming task. Subjects (n=12) had to covertly name either animals or furniture items. Functional scanning was performed using a conventional 1.5-Tesla whole-body MRI system. Images obtained during naming the two categories were compared using a non-parametric test. The study revealed evidence for domain-specific lexical regions in left middle, right middle and inferior frontal areas, as well as in superior and middle temporal areas. The results corroborate neuropsychological data and demonstrate directly and non-invasively in human volunteers that semantic representations in frontal and temporal areas are, to some degree, localized and possibly implemented as multiple maps. A completely distributed storage of semantic information is rendered unlikely.

Adult↗

PubMed1999

Electrophysiological correlates of direct versus indirect semantic priming in normal volunteers.

The N400 component of event related potentials (ERP) was studied in 27 right-handed healthy subjects in a speeded lexical decision task. The semantic distance between primes (always words) and targets (50% words, 50% non-words) was systematically varied. Prime-target relations included directly related words (hen-egg), indirectly related words (lemon-sweet), and non-related words (sofa-wing). ERPs were recorded from 20 scalp electrodes positioned according to the international 10-20 system. The N400 reflected semantic distance with the most negative and latest N400 peak in the non-related condition, the least negative and earliest N400 peak in the direct condition and the peak in the indirect condition in-between. Hence, N400 priming effect in the indirect condition was obtained in the absence of strong sentential constraints and even though the mediating word was physically not present.

Adult↗

PubMedDate not supplied

Semantics, inflammation, cytokines and common sense.

Semantic evaluation of some of the terms we regularly employ--inflammation, anti-inflammatory, pro-inflammatory, anti-inflammatory drugs, cytokines, homeostasis and stress--raises concerns about their precise meanings and about their mechanistic implications. Semantic imprecision may have undesirable conceptual consequences.

Animals↗

PubMed2001

Studying semantics in the brain: the rapid stream stimulation paradigm.

Event-related potentials (ERPs) provide information about the temporal course of cognitive processes in the brain. They have proved to be a valuable tool in order to explore semantic aspects of word processing. However, to date, research in this field has been mostly concerned with the study of post-lexical features by means of the N400-paradigm. We introduce here the rapid stream stimulation paradigm, in which stimuli reflecting different levels of linguistic information are presented to subjects at a high rate of stimulation. The present protocol shows in detail how this paradigm can be applied. The application of the rapid stream stimulation paradigm evokes the recognition potential (RP), an ERP component that peaks at around 260 ms after stimuli onset and seems to be reflecting lexical selection processes. Results of studies that revealed the sensibility of the RP to visual-semantic aspects and the location of its neural generators within basal extrastriate areas are reported. Although some research has been conducted with the rapid stream stimulation paradigm much remains still to be done. Some of the possibilities that this paradigm offers are further discussed.

Brain↗

PubMedDate not supplied

From syntactic-semantic tagging to knowledge discovery in medical texts.

In the GALEN project, the syntactic-semantic tagger MultiTALE is upgraded to extract knowledge from natural language surgical procedure expressions. In this paper, we describe the methodology applied and show that out of a randomly selected sample of such expressions coming from the procedure axis of Snomed International, 81% could be analysed correctly. The problems encountered fall in three different categories: unusual grammatical configurations within the Snomed terms, insufficient domain knowledge and different categorisation of concepts and semantic links in the domain and linguistic models used. It is concluded that the Multi-TALE system can be used to attach meaning to words that not have been encountered previously, but that an interface ontology mediating between domain models and linguistic models is needed to arrive at a higher level of independence from both particular languages and from particular domains.

Forecasting↗

PubMed2000

Common basal extrastriate areas for the semantic processing of words and pictures.

OBJECTIVE: The recognition potential (RP) is an electrophysiological brain response which is sensitive to the semantic processing of meaningful stimuli. In this study we attempt to elucidate the topography and neural origin of the RP evoked by pictures and to compare it with the RP evoked by words. METHODS: Words, pictures, Chinese characters and control stimuli were presented to 20 subjects following the rapid stream stimulation procedure. The activity was recorded using 60 cephalic electrodes. RESULTS: We found a RP displaying its maximal amplitude at the left inferior parieto-occipital electrode (PO7) for words and at the right homologue electrode (PO8) for pictures and Chinese characters. Both the amplitude and the latency of the RP were larger in the case of words. A profile analysis indicated that the neural generators of the RP were common regardless of the type of stimulus, and a dipole analysis placed them about the lingual gyrus. CONCLUSIONS: Words and pictures share the same neural generators for the RP despite of subtle differences in lateralization. This is interpreted as an index of a multimodal semantic processing in basal extrastriate areas.

Adolescent↗

PubMed2002

The potential of latent semantic analysis for machine grading of clinical case summaries.

OBJECTIVE: This paper introduces latent semantic analysis (LSA), a machine learning method for representing the meaning of words, sentences, and texts. LSA induces a high-dimensional semantic space from reading a very large amount of texts. The meaning of words and texts can be represented as vectors in this space and hence can be compared automatically and objectively. PSYCHOLOGICAL THEORY: A generative theory of the mental lexicon based on LSA is described. The word vectors LSA constructs are context free, and each word, irrespective of how many meanings or senses it has, is represented by a single vector. However, when a word is used in different contexts, context appropriate word senses emerge. CURRENT APPLICATIONS: Several applications of LSA to educational software are described, involving the ability of LSA to quickly compare the content of texts, such as an essay written by a student and a target essay. POTENTIAL MEDICAL APPLICATIONS: An LSA-based software tool is sketched for machine grading of clinical case summaries written by medical students.

Artificial Intelligence↗

PubMed1995

Semantic memory and reading abilities: a case report.

We document the unexpected dissociation of preserved reading skills in a patient with severely impaired semantic memory. The common co-occurrence between impairment of word meaning and surface dyslexia has not been observed. The patient (hereafter called DRN) had marked naming and word comprehension difficulties. A strong word frequency effect was observed on tests of word comprehension but was absent in a test of word reading. DRN's ability to read both regular and exception words that he failed to comprehend was remarkably well preserved. We will argue that these findings provide further support for the independence of semantic and phonological processing.

Aged↗

PubMed1995

Knowledge of New English vocabulary in amnesia: an examination of premorbidly acquired semantic memory.

To assess if amnesics have intact remote memory for general semantic information, we examined memory for vocabulary words with known dates of entry into the language between 1955 and 1989. Amnesics of mixed etiology with acute onset performed normally on both a recall and a recognition task. Korsakoff patients, in contrast, were impaired on both tasks and demonstrated a gradient such that their knowledge of words acquired during more recent time periods was worse than that of words acquired during more remote time periods. The improvement in performance associated with recognition testing was larger for Korsakoff patients than for control subjects and correlated significantly with a composite measure of frontal dysfunction. These findings suggest a deficit in the controlled search and retrieval of semantic information in Korsakoff patients. The implications of the differential performance of Korsakoff and mixed etiology amnesics for explanations of temporally graded retrograde amnesia are discussed.

Adult↗

PubMed1999

Differential association of HIV-related neuropsychological impairment with semantic versus repetition priming.

There is evidence that the facilitating effects of stimulus repetition (repetition or identity priming) are mediated by visuoperceptual functions local to extrastriate cortex. Semantic or verbal-associative priming, on the other hand, is believed to be a function of more anterior brain systems. The present study finds evidence for disrupted semantic priming with intact repetition priming in a cognitively impaired HIV+ sample. These results are consistent with recent brain-imaging evidence for a subcortical and white-matter locus for HIV associated neuropathology resulting in effects on subcortical-frontal systems.

Adult↗

PubMed1999

Cross-modal semantic and homograph priming in healthy young, healthy old, and in Alzheimer's disease individuals.

Two experiments are reported that explore the influence of strength of the prime-target relationship on the observed priming effects in young, healthy old, and individuals diagnosed with dementia of the Alzheimer type (DAT). In Experiment 1, participants were auditorily presented primes (FURNITURE) and after varying delays presented visual targets that were (1) high-strength related (e.g., SOFA), (2) low-strength related (e.g., RUG), or (3) unrelated control words (e.g., COW or DEER). The results indicated that the DAT individuals produced relatively larger priming effects that both the young and the healthy old, but these data could be accommodated by increases in effect size due to general slowing of response latencies. In Experiment 2, the same cross-modal priming paradigm was used with ambiguous words presented as primes (e.g., BANK) and either high-dominant (e.g., MONEY) or low-dominant (e.g., RIVER) words as targets. The results of Experiment 2 produced a qualitatively distinct pattern of priming that indicated DAT individuals only produced priming for high-dominant targets and not for low-dominant targets, whereas, the healthy control groups produced equivalent priming for both high- and low-dominant targets. The discussion focuses on the implication that these results have for the interpretation of semantic priming effects, in general, along with implications for the apparent semantic memory loss in DAT individuals.

Adolescent↗

PubMedDate not supplied

Semantic retrieval in DNA-based memories with Gibbs energy models.

At least three types of associative memories based on DNA-affinity have been proposed. Previously, we have quantified the quality of retrieval of genomic and abiotic information in simulation by comparison to state-of-the-art symbolic methods available, such as LSA (Latent Semantic Analysis). Their performance is poor when the evaluation criterion for DNA-affinity is a simple approximation of the Gibbs energy that governs duplex formation for retrievals. Here, we use a more realistic approximation of the Gibbs energy to improve semantic retrievals in DNA memories. Their performance is much closer to that of LSA, according to human expert ratings. With more realistic approximations of DNA affinity, performance is expected to improve for other, more adaptive associative memories with compaction in silico, and even more so with actual DNA molecules in vitro.

Computers, Molecular↗

PubMed2001

Mining the chemical quarry with joint chemical probes: an application of latent semantic structure indexing (LaSSI) and TOPOSIM (Dice) to chemical database mining.

In this study we use a novel similarity search technique called latent semantic structure indexing (LaSSI) with joint chemical probes as queries to mine the MDL drug data report database. LaSSI is based on latent semantic indexing developed for searching textual databases. We use atom pair and topological torsion descriptors in our calculations. The results obtained with LaSSI are compared with another in-house similarity search technique TOPOSIM. The results from the similarity searches using joint chemical probes are significantly better than searches using single chemical probes for both LaSSI and TOPOSIM. The selected molecules are closely related in activity to their queries and are ranked among the top 300 scoring molecules of the 82 860 entries in the database. Our implementation of LaSSI is very fast and efficient in finding active compounds. The results also show that LaSSI consistently retrieves more diverse chemical structures representative of the joint chemical probes in comparison to TOPOSIM. The use of multimolecule topological probes to identify compounds complements the use of searching databases with 3D pharmacophore hypotheses.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed2003

Integration of syntactic and semantic information in predictive processing: cross-linguistic evidence from German and English.

Two visual-world eyetracking experiments were conducted to investigate whether, how, and when syntactic and semantic constraints are integrated and used to predict properties of subsequent input. Experiment 1 contrasted auditory German constructions such as, "The hare-nominative eats ... (the cabbage-acc)" versus "The hare-accusative eats ... (the fox-nom)," presented with a picture containing a hare, fox, cabbage, and distractor. We found that the probabilities of the eye movements to the cabbage and fox before the onset of NP2 were modulated by the case-marking of NP1, indicating that the case-marking (syntactic) information and verbs' semantic constraints are integrated rapidly enough to predict the most plausible NP2 in the scene. Using English versions of the some stimuli in active/passive voice (Experiment 2), we replicated the same effect, but at a slightly earlier position in the sentence. We discuss the discrepancies in the two Germanic languages in terms of the ease of integrating information across, or within, constituents.

Eye Movements↗