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PubMed2001

Repeating without semantics: surface dysphasia?

We describe our investigations of MNA, who had a progressive, severe and global loss of semantic knowledge (semantic dementia). Her verbal vocabulary was restricted to a few common words and she was also unable to recognize common objects from sight. By contrast, she had a well-preserved digit span (7-8 digits). In this series of experiments, we focused on her ability to repeat lists and sentences in which familiarity, meaningfulness, morphology and syntactic structure were manipulated. In list repetition tasks, we found that MNA showed a reliable effect of phonological similarity, word frequency and stimulus lexicality, but was unaffected by linguistic complexity, word length, semantic coherence or the status of individual stimuli as "known" or "unknown". In sentence repetition, her performance was not influenced by any semantic variables. However, there was a substantial effect of the frequency of the constituent vocabulary, even for words outside the range of her retained vocabulary. The influence of syntax was restricted to minor effects of morphology. The phonemes of syllables and the syllables of words are bound by their co-occurrence rather than their meaning. We conclude that the phonological representation of words is functionally independent of the semantic system.

Aged↗

PubMed2001

The neuropsychology of frontal variant frontotemporal dementia and semantic dementia. Introduction to the special topic papers: Part II.

The second part of this review, which accompanies 10 special topic articles dedicated to frontotemporal dementia (FTD), describes some of the advances in understanding frontal variant FTD (fvFTD) and semantic dementia, and the theoretical insights gained into normal cognitive processes from the study of these syndromes. Recent work has clarified the neuropsychiatric features that distinguish fvFTD from Alzheimer's and has begun to spread light on the underlying deficits in social judgement, theory of mind, processing of emotional stimuli and decision making. With regard to central aspects of cognitive processing, such as memory, patients with fvFTD may have a distinctive profile of performance on tests of explicit and implicit memory, and contrary to current views some patients may even have a severe amnesic syndrome. There is also growing evidence that despite relatively well preserved general language skills, patients with fvFTD have particular problems with verb processing. Although there is agreement regarding the key features of semantic dementia, much controversy has surrounded the issue of whether the cognitive findings favour an explanation in terms of progressive breakdown of a central amodal semantic store or differential involvement of verbal and non-verbal systems. Other topics discussed include the impact of semantic breakdown on phonological processes and episodic memory. We also review recent structural and functional neuroimaging findings in semantic dementia.

Dementia↗

PubMed2001

Neural correlates of verbal memory encoding during semantic and structural processing tasks.

Eighteen participants were imaged using fMRI to explore whether brain regions predicting successful verbal memory encoding during semantic decisions would continue to predict encoding during structural (non-semantic) decisions. Consistent with prior studies, left inferior frontal and fusiform regions were more active during semantic than structural decisions, and activity was greater for remembered than forgotten words during semantic decisions. Critically, structural decisions yielded significantly greater activity for remembered than forgotten words in these regions providing evidence that a common frontal-temporal network supports verbal memory encoding irrespective of orienting task. Further analysis revealed activity associated with successful encoding in the right precentral gyrus, suggesting other regions may also play a role in verbal encoding during non-semantic processing.

Adult↗

PubMed2005

Pre-attentive detection of syntactic and semantic errors.

This magnetoencephalographic study tested whether magnetic fields evoked by syntactic and semantic errors differ in their time course and magnitude from fields evoked by phonemic differences. An oddball design, using German sentences with embedded critical words was applied: The error condition (with the standard word RASEN, lawn, in 70% of the trials, and the syntactic and semantic errors ROSEN, roses and RIESEN, giant as deviants) was compared with a neutral, correct phonemic condition. Mismatch responses were significantly larger for syntactic and semantic errors as compared to mere phonemic deviations. The semantic error elicited higher mismatch responses than the syntactic error. This error-sensitive component is interpreted as a very early detector for semantic and syntactic errors.

Attention↗

PubMed2006

Using semantic memory to boost 'episodic' recall in a case of developmental amnesia.

We report two experiments that investigated factors that might boost 'episodic' recall for Jon, a developmental amnesic whose episodic memory is gravely impaired but whose semantic memory seems relatively normal. Experiment 1 showed that Jon's recall improved following a semantic study task compared with a non-semantic study task, as well as following four repeated study trials compared with only one. Experiment 2 additionally revealed that Jon's recall improved after acting compared with reading action phrases at study, but only if the phrases were well integrated semantically. The results provide some support for the hypothesis that Jon's 'episodic' recall depends on the extent to which he is able to retrieve events using semantic memory.

Adult↗

PubMedDate not supplied

Correlation between gene expression and GO semantic similarity.

This research analyzes some aspects of the relationship between gene expression, gene function, and gene annotation. Many recent studies are implicitly based on the assumption that gene products that are biologically and functionally related would maintain this similarity both in their expression profiles as well as in their Gene Ontology (GO) annotation. We analyze how accurate this assumption proves to be using real publicly available data. We also aim to validate a measure of semantic similarity for GO annotation. We use the Pearson correlation coefficient and its absolute value as a measure of similarity between expression profiles of gene products. We explore a number of semantic similarity measures (Resnik, Jiang, and Lin) and compute the similarity between gene products annotated using the GO. Finally, we compute correlation coefficients to compare gene expression similarity against GO semantic similarity. Our results suggest that the Resnik similarity measure outperforms the others and seems better suited for use in Gene Ontology. We also deduce that there seems to be correlation between semantic similarity in the GO annotation and gene expression for the three GO ontologies. We show that this correlation is negligible up to a certain semantic similarity value; then, for higher similarity values, the relationship trend becomes almost linear. These results can be used to augment the knowledge provided by clustering algorithms and in the development of bioinformatic tools for finding and characterizing gene products.

Algorithms↗

PubMed2002

Evaluation and application of a semantic network partition.

Semantic networks (SNs) are excellent knowledge representation structures. However, large semantic networks are hard to comprehend. To overcome this difficulty, several methods of partitioning have been developed that rely on different mixes of structural and semantic methods. However, little has appeared in the literature concerning the question whether a partition of a semantic network creates subnetworks that agree with human insight. We address this issue by presenting a comparison between the results of an algorithmic partitioning method and a partition created by a group of experts. Subsequently, we show how a network partition can be used to generate various partial views of a semantic network, which facilitate user orientation. Examples from the Unified Medical Language System (UMLS) SN are used to demonstrate partial views.

Algorithms↗

PubMed2006

How does the brain mediate interpretation of incongruent auditory emotions? The neural response to prosody in the presence of conflicting lexico-semantic cues.

We frequently encounter conflicting emotion cues. This study examined how the neural response to emotional prosody differed in the presence of congruent and incongruent lexico-semantic cues. Two hypotheses were assessed: (i) decoding emotional prosody with conflicting lexico-semantic cues would activate brain regions associated with cognitive conflict (anterior cingulate and dorsolateral prefrontal cortex) or (ii) the increased attentional load of incongruent cues would modulate the activity of regions that decode emotional prosody (right lateral temporal cortex). While the participants indicated the emotion conveyed by prosody, functional magnetic resonance imaging data were acquired on a 3T scanner using blood oxygenation level-dependent contrast. Using SPM5, the response to congruent cues was contrasted with that to emotional prosody alone, as was the response to incongruent lexico-semantic cues (for the 'cognitive conflict' hypothesis). The right lateral temporal lobe region of interest analyses examined modulation of activity in this brain region between these two contrasts (for the 'prosody cortex' hypothesis). Dorsolateral prefrontal and anterior cingulate cortex activity was not observed, and neither was attentional modulation of activity in right lateral temporal cortex activity. However, decoding emotional prosody with incongruent lexico-semantic cues was strongly associated with left inferior frontal gyrus activity. This specialist form of conflict is therefore not processed by the brain using the same neural resources as non-affective cognitive conflict and neither can it be handled by associated sensory cortex alone. The recruitment of inferior frontal cortex may indicate increased semantic processing demands but other contributory functions of this region should be explored.

Acoustic Stimulation↗

PubMed2004

The effects of noise and gender on children's episodic and semantic memory.

The main objectives in the present study were to examine meaningful irrelevant speech and road traffic noise effects on episodic and semantic memory, and to evaluate whether gender differences in memory performance interact with noise. A total of 96 subjects, aged 13-14 years (n = 16 boys and 16 girls in each of three groups), were randomly assigned to a silent or two noise conditions. Noise effects found were restricted to impairments from meaningful irrelevant speech on recognition and cued recall of a text in episodic memory and of word comprehension in semantic memory. The obtained noise effect suggests that the meaning of the speech were processed semantically by the pupils, which reduced their ability to comprehend a text that also involved processing of meaning. Meaningful irrelevant speech was also assumed to cause a poorer access to the knowledge base in semantic memory. Girls outperformed boys in episodic and semantic memory materials, but these differences did not interact with noise.

Adolescent↗

PubMed2005

Functional neuroanatomy of remote episodic, semantic and spatial memory: a unified account based on multiple trace theory.

We review lesion and neuroimaging evidence on the role of the hippocampus, and other structures, in retention and retrieval of recent and remote memories. We examine episodic, semantic and spatial memory, and show that important distinctions exist among different types of these memories and the structures that mediate them. We argue that retention and retrieval of detailed, vivid autobiographical memories depend on the hippocampal system no matter how long ago they were acquired. Semantic memories, on the other hand, benefit from hippocampal contribution for some time before they can be retrieved independently of the hippocampus. Even semantic memories, however, can have episodic elements associated with them that continue to depend on the hippocampus. Likewise, we distinguish between experientially detailed spatial memories (akin to episodic memory) and more schematic memories (akin to semantic memory) that are sufficient for navigation but not for re-experiencing the environment in which they were acquired. Like their episodic and semantic counterparts, the former type of spatial memory is dependent on the hippocampus no matter how long ago it was acquired, whereas the latter can survive independently of the hippocampus and is represented in extra-hippocampal structures. In short, the evidence reviewed suggests strongly that the function of the hippocampus (and possibly that of related limbic structures) is to help encode, retain, and retrieve experiences, no matter how long ago the events comprising the experience occurred, and no matter whether the memories are episodic or spatial. We conclude that the evidence favours a multiple trace theory (MTT) of memory over two other models: (1) traditional consolidation models which posit that the hippocampus is a time-limited memory structure for all forms of memory; and (2) versions of cognitive map theory which posit that the hippocampus is needed for representing all forms of allocentric space in memory.

Amnesia↗

PubMed1993

Semantic priming and stimulus degradation: implications for the role of the N400 in language processing.

Two experiments explored the effects of stimulus degradation on behavioral and event-related potential (ERP) measures of semantic priming. The primary goal was to help elucidate the psychological processes that underlie the N400 component. In both experiments, subjects made speeded lexical decisions to words and pseudowords preceded by either semantically related or unrelated prime words. In one block of trials, the target stimuli were intact, and in a second block they were degraded by removing a random 33% of the elements making up each letter of the target (Experiment 1) or by overlaying a matrix of dots on the target (Experiment 2). In both experiments, subjects responded faster and more accurately to related targets than to unrelated targets (behavioral semantic priming effect), and this priming effect was greater when the target was degraded. However, although the N400 component was larger for unrelated than related targets (ERP semantic priming effect), there was no evidence that this difference was larger in the degraded block of either experiment. These results indicate that the behavioral and ERP measures reported here appear to be tapping into different components of the process(es) involved in semantic priming. The implication of the results for the linguistic processes underlying the N400 are discussed.

Adolescent↗

PubMed2006

An electrophysiological investigation of indirect semantic priming.

In two experiments, direct and indirect semantic priming were measured using event-related potentials. In Experiment 1, participants rated the relatedness between prime and target on a seven-point scale. In Experiment 2, participants simply read the primes and targets as they monitored for a semantic category in probe filler items. Significant direct and indirect N400 priming effects were observed in both experiments. In Experiment 1, the indirect N400 priming effect remained significant when indirectly related and unrelated word pairs were matched for participants' explicit relatedness judgments. In both experiments, the indirect N400 priming effects were preserved when indirectly related and unrelated word pairs were matched on more global and objective measures of semantic similarity. These findings are discussed in the context of current theoretical models of semantic memory and semantic priming.

Adult↗

PubMedDate not supplied

Auditory event-related potentials during phonetic and semantic processing in children.

This study was designed to follow the time course of different levels of linguistic processing using auditory event-related potentials (AERPs). A hierarchical set of acoustically controlled stimuli was used to elicit AERPs in 20 normal children who performed discrimination tasks involving pure tones, phonetic 'easy' and 'difficult' stimuli and semantic stimuli. Results show that (1) AERP latencies were similar for phonetic 'easy' and 'difficult' stimuli, (2) prolonged P(2), N(2) and P(3) latencies characterized semantic processing compared to phonetic processing, (3) a late negativity was elicited during semantic processing only, (4) P(3) amplitudes were larger over the left compared to right scalp during linguistic processing (phonetic and semantic) but were similar during nonlinguistic processing (pure tones) and (5) reaction time was found to be longest for semantic processing whereas performance accuracy was found to be an insensitive measure. These results provide insight into brain processes underlying the perception of speech. Furthermore, they support a dual model of speech perception that includes parallel and serial processing.

Adolescent↗

PubMedDate not supplied

The influence of semantic and syntactic context constraints on lexical selection and integration in spoken-word comprehension as revealed by ERPs.

An event-related brain potential experiment was carried out to investigate the influence of semantic and syntactic context constraints on lexical selection and integration in spoken-word comprehension. Subjects were presented with constraining spoken sentences that contained a critical word that was either (a) congruent, (b) semantically and syntactically incongruent, but beginning with the same initial phonemes as the congruent critical word, or (c) semantically and syntactically incongruent, beginning with phonemes that differed from the congruent critical word. Relative to the congruent condition, an N200 effect reflecting difficulty in the lexical selection process was obtained in the semantically and syntactically incongruent condition where word onset differed from that of the congruent critical word. Both incongruent conditions elicited a large N400 followed by a left anterior negativity (LAN) time-locked to the moment of word category violation and a P600 effect. These results would best fit within a cascaded model of spoken-word processing, proclaiming an optimal use of contextual information during spoken-word identification by allowing for semantic and syntactic processing to take place in parallel after bottom-up activation of a set of candidates, and lexical integration to proceed with a limited number of candidates that still match the acoustic input.

Acoustic Stimulation↗

PubMed2004

The functional neuroanatomy of episodic and semantic autobiographical remembering: a prospective functional MRI study.

Autobiographical memory comprises episodic and semantic components mediated by dissociable states of consciousness, one promoting the experience of the self at a specific moment in the past, and the other involving self-knowledge that does not require ''mental time travel.'' These components can be difficult to dissociate using retrospective autobiographical stimuli collection. In this study, we manipulated the episodic/semantic distinction within prospectively collected autobiographical stimuli. Over several months, participants made recordings documenting specific episodes, repeated episodes, and world knowledge. These recordings were later played back to participants during scanning with functional MRI. The results indicated overlapping but distinct patterns of brain activity corresponding to episodic and semantic autobiographical memory. Both episodic and semantic autobiographical memory engaged the left anteromedial prefrontal cortex associated with self-reference, but the episodic condition did so to a greater degree. The episodic condition uniquely engaged the medial temporal, posterior cingulate, and diencephalic regions associated with remote memory recovery. Whereas the episodic condition engaged the right temporo-parietal cortex involved in reconstruction of spatial context and attentional orienting, the semantic condition engaged the left temporo-parietal and parieto-frontal systems involved in egocentric spatial processing and top-down attentional control. Episodic recollection was also associated with suppression of emotional paralimbic regions. These findings support a functional neuroanatomical dissociation between episodic and semantic autobiographical memory, providing concordance to amnesic syndromes with disproportionate impairment in one of these two forms of autobiographical memory.

Adult↗

PubMed2005

Brain responses to segmentally and tonally induced semantic violations in Cantonese.

The present event-related potential (ERP) study examined the role of tone and segmental information in Cantonese word processing. To this end, participants listened to sentences that were either semantically correct or contained a semantically incorrect word. Semantically incorrect words differed from the most expected sentence completion at the tone level, at the segmental level, or at both levels. All semantically incorrect words elicited an increased frontal negativity that was maximal 300 msec following word onset and an increased centroparietal positivity that was maximal 650 msec following word onset. There were differences between completely incongruous words and the other two violation conditions with respect to the latency and amplitude of the ERP effects. These differences may be due to differences in the onset of acoustic deviation of the presented from the expected word and different mechanisms involved in the processing of complete as compared to partial acoustic deviations. Most importantly, however, tonally and segmentally induced semantic violations were comparable. This suggests that listeners access tone and segmental information at a similar point in time and that both types of information play comparable roles during word processing in Cantonese.

Acoustic Stimulation↗

PubMed2005

Phonotactic knowledge and lexical-semantic processing in one-year-olds: brain responses to words and nonsense words in picture contexts.

During their first year of life, infants not only acquire probabilistic knowledge about the phonetic, prosodic, and phonotactic organization of their native language, but also begin to establish first lexical-semantic representations. The present study investigated the sensitivity to phonotactic regularities and its impact on semantic processing in 1-year-olds. We applied the method of event-related brain potentials to 12- and 19-month-old children and to an adult control group. While looking at pictures of known objects, subjects listened to spoken nonsense words that were phonotactically legal (pseudowords) or had phonotactically illegal word onsets (nonwords), or to real words that were either congruous or incongruous to the picture contents. In 19-month-olds and in adults, incongruous words and pseudowords, but not nonwords, elicited an N400 known to ref lect mechanisms of semantic integration. For congruous words, the N400 was attenuated by semantic priming. In contrast, 12-month-olds did not show an N400 difference, neither between pseudo- and nonwords nor between incongruous and congruous words. Both 1-year-old groups and adults additionally displayed a lexical priming effect for congruous words, that is, a negativity starting around 100 msec after words onset. One-year-olds, moreover, displayed a phonotactic familiarity effect, that is, a widely distributed negativity starting around 250 msec in 19-month-olds but occurring later in 12-month-olds. The results imply that both lexical priming and phonotactic familiarity already affect the processing of acoustic stimuli in children at 12 months of age. In 19-month-olds, adult-like mechanisms of semantic integration are present in response to phonotactically legal, but not to phonotactically illegal, nonsense words, indicating that children at this age treat pseudowords, but not nonwords, as potential word candidates.

Acoustic Stimulation↗

PubMed2006

"Presemantic" cognition in semantic dementia: six deficits in search of an explanation.

On the basis of a theory about the role of semantic knowledge in the recognition and production of familiar words and objects, we predicted that patients with semantic dementia would reveal a specific pattern of impairment on six different tasks typically considered "pre-" or "non-" semantic: reading aloud, writing to dictation, inflecting verbs, lexical decision, object decision, and delayed copy drawing. The prediction was that all tasks would reveal a frequency-by-typicality interaction, with patients performing especially poorly on lower-frequency items with atypical structure (e.g., words with an atypical spelling-to-sound relationship; objects with an atypical feature for their class, such as the hump on a camel, etc). Of 84 critical observations (14 patients performing 6 tasks), this prediction was correct in 84/84 cases; and a single component in a factor analysis accounted for 87% of the variance across seven measures: each patient's degree of impairment on atypical items in the six experimental tasks and a separate composite score reflecting his or her degree of semantic impairment. Errors also consistently conformed to the predicted pattern for both expressive and receptive tasks, with responses reflecting residual knowledge about the typical surface structure of each domain. We argue that these results cannot be explained as associated but unrelated deficits but instead are a principled consequence of a primary semantic impairment.

Aged↗