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PubMedDate not supplied

Effects of age and education on the lexico-semantic content of connected speech in adults.

One hundred and thirty-three subjects who considered themselves to be in good health described the bank robbery picture from an aphasia battery for French-speaking subjects. The subjects' connected speech was analyzed and various lexico-semantic measures were obtained. For the purposes of analysis, the subjects were grouped according to age and education level. Results demonstrated that subjects with fewer years of education produced less content than subjects with higher levels of education. Age also affected subjects' performance but only when considering efficiency, the number of content units as a function of time, and the number of different open-class words as a function of time. Older subjects tended to repeat the same content units (using mostly the same words) and comment on some word-finding difficulties they experienced. These behaviors may explain why older subjects were less efficient in the transmission of lexico-semantic information. The results emphasize how age can affect lexico-semantic performance, and add new data about the effects of education, which should be taken into consideration when assessing persons who may show signs of a language disorder.

Adult↗

PubMed2000

Minding the facts: a comment on Thompson-Schill et al.'s "A neural basis for category and modality specificity of semantic knowledge".

In this comment on a recent paper by Thompson-Schill et al. (1999) I argue that the authors failed to consider important empirical facts that are at variance with their favored theory of the causes of semantic category-specific deficits. I also argue that the predictions they make about fusiform gyrus activation on the basis of the interactive modality-specific hypothesis of semantic organization do not obviously follow from that model. I point out that simulations are needed in order to derive predictions from the model. Finally, I argue that the fMRI results they obtained are not obviously relevant to our understanding of the causes of semantic category-specific deficits.

Auditory Perception↗

PubMed2000

Electrophysiological dissociation between verbal and nonverbal semantic processing in learning disabled adults.

Event-related potentials (ERPs) were recorded as 16 adults with learning disabilities (LD) and 16 controls were presented with two sets of stimuli. The first set comprised pairs of line drawings and environmental sounds (nonverbal condition); the second consisted of printed and spoken words (verbal condition). In the controls, semantically related items elicited smaller N400s than unrelated items in both conditions, with opposing hemispheric asymmetries for spoken words and environmental sounds. The LD group did not show a significant difference between related and unrelated words, despite a robust context effect for nonspeech sounds. The results suggest anomalous processing limited to the verbal domain in a simple semantic association task in the LD group. Semantic deficits in this group may reflect a relatively specific deficit in forming verbal associations rather than a more general difficulty that spans both verbal and nonverbal domains.

Adolescent↗

PubMed2002

Verbal fluency in Huntington's disease: a longitudinal analysis of phonemic and semantic clustering and switching.

Two underlying components of verbal fluency tasks have been identified as clustering (the ability to generate successive words within a sub-category) and switching (the ability to shift from one sub-category to another). Selective impairment of switching ability occurs in patients with frontostriatal pathology, whilst clustering ability is compromised with temporal lobe dysfunction. Letter fluency tasks have been shown to be especially sensitive to frontostriatal deficits, whereas, category fluency tasks tend to be compromised by temporal lobe pathology. This study examined two types of verbal fluency task (letter fluency and category fluency) using two levels of analysis (phonemic and semantic) for clustering and switching measures. The performance of 21 frontostriatally compromised Huntington's disease (HD) patients was followed over an average of 3.5 annual follow-up visits. HD patients showed a significant reduction of correctly generated words over time, together with a significant increase in word repetitions. Phonemic switching decreased significantly over time for both letter and category fluency. Semantic switching, however, remained stable over time for both verbal fluency tasks. Clustering (both semantic and phonemic) likewise remained stable and did not vary longitudinally for either letter or category fluency. Hence, phonemic switching alone drove verbal fluency performance and this selective impairment can be explained by the progressive involvement of frontostriatal circuitry in the natural progression of HD.

Adult↗

PubMed1997

Automatic semantic priming of nouns and verbs in patients with Alzheimer's disease.

The status of semantic representations of nouns (concrete and abstract) and verbs (motion and non-motion) was investigated in patients with Alzheimer's disease (AD). Nouns and verbs have been argued to activate different neural substrates, given the selective difficulties reported for one or the other grammatical class in patients with focal lesions. Additionally, category-specific deficits have been reported for either abstract or concrete words, often in patients with bilateral neuropathology. We looked for these types of dissociations in patients with AD in a semantic priming experiment using a pronunciation task and a short stimulus onset asynchrony. The normal control subjects demonstrated automatic activation for both concrete nouns and motion verbs. The AD patients, however, demonstrated priming effects for concrete nouns, but not for motion verbs. This dissociation between concrete nouns and motion verbs found for the AD patients is discussed in terms of differences in the nature of semantic representations involving multiple physical and functional attributes in the case of concrete nouns, but only motion attributes in the case of motion verbs. Moreover, the typical distribution of neuropathology associated with AD may put motion verbs at risk, particularly given the neuroanatomical considerations suggested by recent positron emission tomography (PET) studies.

Aged↗

PubMed1999

Differences in semantic category priming in the left and right cerebral hemispheres under automatic and controlled processing conditions.

The contribution of each cerebral hemisphere to the generation of semantic category meanings at automatic and strategic levels of processing was investigated in a priming experiment where prime and target words were independently projected to the left or right visual fields (LVF or RVF). Non-associated category exemplars were employed as related pairs in a lexical decision task and presented in two experimental conditions. The first condition was designed to elicit automatic processing, so related pairs comprised 20% of the positive set, stimulus pairs were temporally separated by a stimulus onset asynchrony (SOA) of 250 ms, and there was no allusion to the presence of related pairs in the instructions to subjects. The second condition, designed to invoke controlled processing, incorporated a relatedness proportion of 50%, stimulus pairs separated by an SOA of 750 ms, and instructions which informed subjects of the presence and use of category exemplar pairs in the stimulus set. In the first condition, a prime directed to either visual field facilitated responses to categorically related targets subsequently projected to the RVF, while in the second condition a prime directed to either visual field facilitated responses to related targets projected to the LVF. The facilitation effects obtained in both conditions appeared to reflect automatic processes, while strategic processes were invoked in the left, but not the right hemisphere in the second condition. The results suggest that both hemispheres have automatic access to semantic category meanings, although the timecourse of activation of semantic category meanings is slower in the right hemisphere than in the left.

Adult↗

PubMed2002

Semantic range and relevance of emotive utterances in patients with frontotemporal degeneration.

Patterns of aberrant language due to lateralized frontal brain lesions have been described. The present study investigated the consequences of lateralized lesion for aspects of semantic range and relevance in speech of patients with frontotemporal degeneration. Demented patients with predominantly left (n=10) and right (n=4) brain degeneration as well as 5 healthy controls participated. Significant differences were found concerning semantic range and relevance in descriptions of emotionally loaded pictures within the demented group and between the demented group and the controls. The demented individuals' speech was less varied and relevant in contrast to the healthy individuals. The speech of the left hemispheric group was more relevant but also more stereotypic and unspecified than that of the right hemispheric group. The results are discussed in terms of impaired semantic retrieval and in relation to lateralization of lesion.

Affect↗

PubMed2003

Pervasive influence of semantics in letter and category fluency: a multidimensional approach.

We used multidimensional statistical procedures to study semantic and lexical processes underlying word retrieval in verbal-fluency performance. Forty healthy participants were given a two-choice letter task (i.e., generate items beginning with the letter 'A' or 'F', in any order) and a two-choice category task (i.e., generate animal or fruit names, in any order). Using correspondence analysis (CoA) and hierarchical clustering (HC), we found evidence of prominent semantic organization in both letter and category fluency. For example, a striking categorical segregation between animate and inanimate entities emerged during the letter task. Analysis of inter-item times revealed strong sequential priming effects in both tasks. Taken together, these results indicate that semantic facilitation is pervasive in word retrieval processes, even in the letter-fluency task, and therefore suggest that the traditional view of letter fluency as a purely phonemically based task should be revised. Finally, our findings may help explain patterns of verbal-fluency measures obtained in focal brain lesion patients.

Adult↗

PubMed2004

Category size effects in semantic and letter fluency in Alzheimer's patients.

Many studies have found that patients with Alzheimer's disease (AD) perform significantly worse than normal controls on verbal fluency tasks. Moreover, some studies have found that AD patients' deficits compared to controls are more severe for semantic fluency (e.g., vegetables) than for letter fluency (e.g. words that begin with F). These studies, however, have not taken category size into account. A comparison of AD patients and age-matched controls on three semantic and three letter categories revealed that both the size and type of a category significantly predicted AD patients' deficits on verbal fluency tasks. These results suggest that the verbal fluency of AD patients will be most attenuated on large semantic categories.

Aged↗

PubMedDate not supplied

Semantic category effect and emotional valence in female university students.

The semantic category effect represents a category dissociation between biological and nonbiological objects in picture naming. The aim of this preliminary study was to further examine this phenomenon, and to explore the possible association between the effect and subjective emotional valence for the named objects. Using a speeded picture naming task, vocal reaction times for 45 items were divided into four categories based on emotional valence rating and semantic category, and examined in 36 female university students. Analyses of the data indicated an "animate/inanimate" category dissociation favouring animate objects, in tandem with a potential relationship between subjective emotional valence and semantic processing underlying picture naming.

Emotions↗

PubMed2003

Processing of semantic categorical and associative relations: an ERP mapping study.

Brain imaging studies have repeatedly shown a dominant involvement of the left hemisphere (LH) in the processing of semantic information. However, some behavioural studies have suggested that the right hemisphere (RH) also processes lexico-semantic information although in a qualitatively different way. More specifically, it has been proposed that the LH shows a greater sensitivity to categorical (CR, or intraconceptual) relationships, while the RH appears more sensitive to associative (AR, or interconceptual) ones. Using semantically unrelated and related word pairs comprised of CR and AR, our aim in this study was to verify the involvement of the RH in the processing of associative relationships. Strength-independent topographical analysis of ERP map series using temporal segmentation procedures showed the same sequence of eight stable map segments in CR and AR conditions. Statistical analysis revealed no difference between conditions either in terms of duration or in terms of time of occurrence of the segmentation maps. However, field strength comparisons between the two conditions using the global field power measure at each time point revealed higher field strength in CR than in AR condition between 300 and 330 ms. Distributed source localisation showed a similar pattern of activation during this time period, involving predominantly left frontal regions. Nevertheless, the strength of the source found in the left medial frontal gyrus differed between CR than AR conditions, thus explaining the differences observed in field strength. Our data suggest that the processing of CR and AR words depend on the same neural network in the LH.

Adolescent↗

PubMed1999

Form and content: dissociating syntax and semantics in sentence comprehension.

The distinction between syntax (sentence form) and semantics (sentence meaning) is fundamental to our thinking about language. Whether and where this distinction is represented at the neural level is still a matter of considerable debate. In the present fMRI study, we examined the neural correlates of syntactic and semantic functions using an innovative activation paradigm specifically designed to unequivocally disentangle syntactic from lexicosemantic aspects of sentence processing. Our findings strongly indicate that a part of Broca's area (BA 44, pars opercularis) is critically implicated in processing syntactic information, whereas the lower portion of the left inferior frontal gyrus (BA 47, pars orbitalis) is selectively involved in processing the semantic aspects of a sentence.

Adult↗

PubMed2003

Hemispheric dissociation in access to the human semantic system.

Patient studies suggest that speech and environmental sounds are differentially processed by the left and right hemispheres. Here, using functional imaging in normal subjects, we compared semantic processing of spoken words to equivalent processing of environmental sounds, after controlling for low-level perceptual differences. Words enhanced activation in left anterior and posterior superior temporal regions, while environmental sounds enhanced activation in a right posterior superior temporal region. This left/right dissociation was unchanged by different attentional/working memory contexts, but it was specific to tasks requiring semantic analysis. While semantic processing involves widely distributed networks in both hemispheres, our results support the hypothesis of a dual access route specific for verbal and nonverbal material, respectively.

Acoustic Stimulation↗

PubMed2004

Temporal lobe abnormalities in semantic processing by criminal psychopaths as revealed by functional magnetic resonance imaging.

We tested the hypothesis that psychopathy is associated with abnormalities in semantic processing of linguistic information. Functional magnetic resonance imaging (fMRI) was used to elucidate and characterize the neural architecture underlying lexico-semantic processes in criminal psychopathic individuals and in a group of matched control participants. Participants performed a lexical decision task in which blocks of linguistic stimuli alternated with a resting baseline condition. In each lexical decision block, the stimuli were either concrete words and pseudowords or abstract words and pseudowords. Consistent with our hypothesis, psychopathic individuals, relative to controls, showed poorer behavioral performance for processing abstract words. Analysis of the fMRI data for both groups indicated that processing of word stimuli, compared with the resting baseline condition, was associated with neural activation in bilateral fusiform gyrus, anterior cingulate, left middle temporal gyrus, right posterior superior temporal gyrus, and left and right inferior frontal gyrus. Analyses confirmed our prediction that psychopathic individuals would fail to show the appropriate neural differentiation between abstract and concrete stimuli in the right anterior temporal gyrus and surrounding cortex. The results are consistent with other studies of semantic processing in psychopathy and support the theory that psychopathy is associated with right hemisphere abnormalities for processing conceptually abstract material.

Adult↗

PubMed2001

The time course of semantic category processing in the cerebral hemispheres: an electrophysiological study.

Using visual half-field presentations of words to the right (RVF) and to the left visual field (LVF), this study investigated the time course of the hemispheric involvement in the processing of semantic category information. Multi-channel event related brain potentials (ERPs) were recorded from 15 healthy subjects during a categorisation task of sequentially presented word pairs. Subjects had to judge mentally after the appearance of the second word whether the words of a pair were semantically related (SR) or not (SU). ERPs were computed, from 100 ms before the onset of the second word to 600 ms, for SR and SU conditions in the LVF and in the RVF separately. The temporal segmentation of ERP map series into sequences of quasi-stable map configurations revealed a total of seven segments in each visual field of which only the first five (S1-S5, appearing between 70 and 400 ms) showed different map configurations as a function of visual field but presented a similar temporal sequence in both visual fields. By contrast, of the last two segments (S6 and S7) which appeared between approximately 400 and approximately 600 ms, only S7 differentiated SR and SU conditions in terms of its duration. Source localisation analysis of the segments showed that following the initial activation of posterior brain regions as a function of the visual field of presentation, a common neural network was activated in the left hemisphere (LH) although the dynamics of activation varied as a function of visual field. Concerning the role of the right hemisphere (RH) in lexico-semantic processing, the results presented here appear to be compatible with a 'callosal relay model' and suggest that, in healthy subjects, information is transferred rapidly ( approximately 150 ms) from the RH to the language dominant-LH.

Adult↗

PubMed2001

Phase-locked gamma band responses to semantic violation stimuli.

This paper addresses the role of gamma-band activity in semantic networks associated with the processing of words and sentences in humans. Magnetoencephalography (MEG) was used to compare the responses of eleven normal volunteers to semantically congruous and incongruous words at the end of syntactically correct sentences. The averaged low frequency responses evoked by the two word classes were clearly different within the latency range associated with N400 components. The oscillatory characteristics of the evoked responses were analysed using Gabor transform techniques in conjunction with statistical re-sampling. This revealed transient gamma-oscillations ( approximately 35 Hz) that were significantly phase-locked to both types of stimuli but preferentially present at intermediate ( approximately 300 ms) and long (>500 ms) latencies for incongruous words. This stimulus dependent phase locked gamma-activity occurred at latencies that were distinct from the short latency and evoked N400 components. The findings suggest that synchronised oscillations provide independent information about brain dynamics and that some semantic processes may dissociate into distinct functional stages.

Adult↗

PubMed2003

High density ERP indices of conscious and unconscious semantic priming.

The existence of differential brain mechanisms of conscious and unconscious processing is a matter of debate nowadays. The present experiment explores whether conscious and unconscious semantic priming in a lexical decision task at a long prime-target stimulus onset asynchrony (SOA) correlate with overlapping or different event related potential (ERP) effects. Results show that the N400 effect, which appeared when words were consciously perceived, completely disappeared when primes were masked at a level where the ability of participants to detect the prime was near chance. Instead, a rather different set of ERP effects was found to index unconscious semantic priming. This suggests that the processes at the basis of conscious and unconscious semantic analyses can under some circumstances be rather different. Moreover, our results support the notion that conscious and unconscious processes are at least partially separable in the brain.

Adult↗

PubMed2003

Neural correlates of error detection and correction in a semantic retrieval task.

Event-related potentials (ERPs) were used to investigate the cognitive and neural substrates of immediate and 1-week delayed error correction in a semantic retrieval task. In particular, we pursued the basis for the 'hypercorrection' effect, the finding that erroneous responses endorsed as correct with high confidence are more likely than low-confidence errors to be corrected at retest. Presentation of negative, but not positive feedback about the accuracy of one's response elicited a fronto-central negativity, similar to the ERN, which was somewhat sensitive to the degree to which negative feedback violated expectation. A fronto-central positivity, similar to the novelty-P3/P3a, more generally indexed detection of a metamemory error, given that it was larger in conditions of high metamemory mismatch than in conditions of low metamemory mismatch, irrespective of absolute task accuracy. For errors, amplitude of the fronto-central positivity, but not the preceding negativity, was correlated with correction on an immediate retest. Thus, to the extent that the fronto-central positivity indexes an orienting response, this response appears to facilitate initial encoding processes, but does not play a key role in memory consolidation. In contrast, a broad, inferior-temporal negativity occurring 300-600 ms after presentation of the correct answer was sensitive to subsequent memory performance at both immediate and delayed retests, but only for answers containing familiar semantic information. This negativity may reflect processes involved in the formation of an association between the question and pre-existing semantic information.

Adult↗