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PubMed2003

Semantic and syntactic processes during sentence comprehension in patients with schizophrenia: evidence from event-related potentials.

Language and thought disorders are core symptoms in schizophrenia. We therefore studied language comprehension processes in patients with schizophrenia and control subjects during a sentence processing paradigm using event-related potentials (ERPs). In the ERP, assignment of syntactic structure to a string of words is reflected by an early left anterior negativity (ELAN) at about 80 ms after stimulus onset. Integration of syntactic and semantic information into a coherent representation is indexed by a positive potential at 600 ms (P600). Amplitudes of the ELAN and the P600 components are higher for grammatically incorrect sentences. Semantic processes are associated with a negative deflection peaking at 400 ms (N400). N400 amplitude is higher in semantically incongruent sentences. Nineteen patients with DSM IV schizophrenia and 19 healthy controls were presented with correct, semantically incorrect (semantic mismatch) and grammatically incorrect sentences (syntactic mismatch). Syntactic mismatch elicited an ELAN component in both subject groups. However, only controls but not patients with schizophrenia exhibited a P600 syntactic mismatch effect. Semantic mismatch was associated with a larger N400 potential which did not differ between groups. These results suggest that patients with schizophrenia are not impaired in syntactic structure assignment as reflected by the ELAN, but show deficits in semantic-syntactic integration processes underlying the P600.

Adult↗

PubMed2003

Electrophysiological comparison of grammatical processing and semantic processing of single spoken nouns.

Access to meaning from speech input is a high-speed process. However, models of word comprehension stipulate that words must be analyzed at phonological, grammatical and semantic levels. Here we used event-related potentials (ERPs) to compare on-line semantic categorization (natural/manufactured) and grammatical gender categorization (masculine/feminine) of spoken monosyllabic French noun pairs. Twenty four native French speakers were instructed to spot pairs of nouns in which both stimuli pertained to a category specified prior to each block. They could make a decision either after processing the first noun (i.e., ignore the second, Release condition), or after processing both (Hold condition). Virtually identical N4 components affecting Hold and Release ERPs in relation to category expectations were elicited by the first noun in both the tasks. Their topography was intermediary between that of the N400 and that of the Left Anterior Negativity. Despite shorter Release reaction times (RTs) for gender decisions than semantic ones, Release and Hold ERPs diverged 84 ms earlier in the semantic context than in the gender context, indicating faster onset for the processing of meaning. Conversely, the offset of Hold/Release differences was observed 42 ms earlier in the gender task than in the semantic task, suggesting an earlier completion for gender categorization. In sum, electrophysiological differences induced by semantic operations commenced earlier but recovered later than those relating to grammatical gender analysis. In convergence with previous Lateralized Readiness Potential and N200 studies, our results suggest that conscious semantic access can precede access to other types of lexical information during word comprehension in highly controlled conditions.

Adult↗

PubMed1996

Nonfluent progressive aphasia and semantic dementia: a comparative neuropsychological study.

Two patients with nonfluent progressive aphasia, who have been studied longitudinally, are contrasted with a group of 5 patients with fluent progressive aphasia or semantic dementia. The most prominent feature of the nonfluent syndrome is the severe distortion of speech output with phonological errors and agrammatic sentence structure. This contrasts with the fluent, well articulated and syntactically correct, but empty, anomic speech found in semantic dementia. Performance on tests of comprehension separates the patient groups: The nonfluent patients show normal single-word comprehension, but marked impairment on tests of syntactic comprehension, while those with semantic dementia demonstrate the opposite pattern. Category fluency is severely defective in semantic dementia, but initial letter-based fluency is more impaired in the nonfluent syndrome. Performance on nonverbally mediated tests of semantic knowledge is impaired in semantic dementia only. The 2 forms of progressive aphasia have in common the sparing of perceptual and visuospatial skills, nonverbal problem solving abilities, and day-to-day (episodic) memory. Neuroradiological investigations have shown marked selective and striking inferolateral left temporal lobe atrophy in all 5 patients with semantic dementia. The changes in nonfluent progressive aphasia appear to be less focal and involve left perisylvian structures more diffusely. These 2 forms of progressive aphasia are, we argue, distinct in their manifestations.

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PubMed2006

Effectiveness of contextual repetition priming treatments for anomia depends on intact access to semantics.

Naming of two semantically impaired aphasic patients was treated with the contextual repetition priming technique, which involves repeated repetition of names of pictures that are related semantically, phonologically, or are unrelated. Our previous studies using this technique have suggested that patients with impaired access to lexical-semantic representations benefit in the short-term from this treatment technique, but show no long-term improvement in naming. In contrast, patients with good access to semantics show short- and long-term benefits from this treatment. Here we report two studies of treatment for two individuals with aphasia affecting access to lexical semantics and anomia but spared access to input and output phonology and spared conceptual semantics. We predicted that they would show short-term facilitation from the contextual priming, but no long-term improvements in naming. The results confirmed the prediction. An account of this pattern is offered within the framework of an interactive activation model of word retrieval. Additionally, we discuss alternative techniques for addressing naming deficits when access to semantics is impaired.

Adult↗

PubMed2001

Semantic factors in the production of number agreement.

This paper examines the role of semantic factors in the production of subject-verb number agreement. As an ostensibly grammatical process, number agreement provides an interesting case for examining the flow and interaction of semantic and syntactic information through the language-production system. Using a sentence-completion task, agreement errors can be elicited from subjects by presenting them with sentence fragments containing a complex noun-phrase, in which the nonhead noun is plural (e.g., The key to the cabinets ... WERE missing.). Previous research has demonstrated that the probability of making an error can be affected by varying the properties of the nouns in the complex noun phrase. By investigating which variables do and do not affect error rates, constraints on the flow of information through the production system can be inferred. In three experiments, we investigated the possible effects of three different semantic manipulations of the nouns in the complex NP: animacy, semantic overlap, and plausibility of modification by the sentence predicate. We found that both animacy and semantic relatedness had reliable effects on error rates, indicating that the mechanism involved in implementing agreement cannot be blind to semantic information. However, the plausibility with which each noun could serve as the subject of the sentence predicate had no effect on error rates. Taken together, these results suggest that while semantic information is visible to the agreement mechanism, there are still constraints on when this information can affect the process. Specifically, it may be the case that only information contained within the complex NP is considered for the purposes of implementing agreement.

Humans↗

PubMed2004

The processing of semantic meaning in Chinese words and evoked brain topography.

The connotative meaning of words can be quantified statistically by the "semantic differential technique" resulting in statistically defined, independent dimensions where every word is uniquely located on the three dimensional evaluation. In an earlier study on German subjects we demonstrated that there are electrophysiological correlates of these meaning dimensions. Here a group of 55 Chinese adults was investigated in two experiments: first, 210 nouns were rated by 32 subjects, and factor analysis on the questionnaire data yielded three independent semantic dimensions. Semantically unique words stemming from these results were then used as stimuli in electrophysiological experiments in another group of 23 healthy right-handed adults. Words of similar physical appearance belonging to different semantic classes were presented visually in random order. The EEG was recorded from 29 channels, and evoked brain activity was computed for each semantic class. Significant differences in electrical brain activation between these semantic word classes were observed as early as 80 ms after stimulus onset, confirming earlier reports on similar findings in German subjects. Further similarities were revealed by a direct comparison of the topographical distribution of potential components elicited by words, and by the results of spatial PCA performed on both sets of data. These results illustrate similar early neural activation based on semantic class, in subject groups of different language and culture.

Adult↗

PubMed1997

The long and short of semantic priming effects in lexical decision.

Unlike other forms of priming, semantic priming appears only to occur at short lags. In apparent contrast to this, S. Becker, M. Moscovitch, M. Behrmann, and S. Joordens (1997) described a theory of priming that predicts long-term effects for all forms of relatedness. This prediction is reconciled with previous failures to observe long-term semantic priming on the basis of 2 claims: (a) that previously used pairs share few semantic features and (b) that tasks typically used to study priming are not especially sensitive to semantic influences. The present experiments provide further support for these claims by demonstrating long-term semantic priming in the lexical-decision task when the stimuli and task are modified in a way that increases semantic involvement. However, the findings' suggest that in addition to the mechanism advocated by Becker et al., a second mechanism is necessary to provide a complete account of semantic priming effects.

Adult↗

PubMed2001

Attention constraints of semantic activation during visual word recognition.

The reduction of semantic priming following letter search of the prime suggests that semantic activation can be blocked if attention is allocated to the letter level during word processing. Is this true even for the very fast-acting component of semantic activation? To test this, the authors explored semantic priming of lexical decision at stimulus onset asynchronies (SOAs) of either 200 or 1,000 ms. Following semantic prime processing, priming occurred at both SOAs. In contrast, no priming occurred at the long SOA following letter-level processing. Of greatest interest, at the short SOA there was priming following the less demanding consonant/vowel task but not following the more attention-demanding letter search task. Hence, semantic activation can occur even when attention is directed to the letter level, provided there are sufficient resources to support this activation. The authors conclude that the default setting during word recognition is for fast-acting activation of the semantic system.

Adult↗

PubMed2005

Characteristics of verbal semantic impairment in left hemisphere epilepsy.

Fifty-two patients with partial epilepsy of left (n=30) or right (n=22) hemisphere origin were compared with 23 healthy subjects to explore the characteristics and mechanisms of verbal semantic deficits. Picture Naming, Picture Pointing, and the Semantic Questionnaire assessed semantic retrieval, comprehension, and judgment, respectively. In comparison with the controls and right hemisphere patients, the left hemisphere patients showed impairments on Picture Naming and the Semantic Questionnaire. On Picture Naming, the left hemisphere patients made significant omissions and intracategorical errors; on the Semantic Questionnaire, they made errors at superordinate and subordinate levels of information, they made more errors in relation to living than nonliving things, and there were significant associations between their Picture Naming and Semantic Questionnaire scores. In this population, the mixed profiles of semantic deficits suggests the coexistence of altered retrieval and information loss.

Adult↗

PubMed2007

Disparate letter and semantic category fluency deficits in autopsy-confirmed frontotemporal dementia and Alzheimer's disease.

Patients with autopsy-confirmed frontotemporal dementia (FTD; n = 16) and Alzheimer's disease (AD; n = 32) were compared on first-letter and semantic category fluency tasks. Despite being matched on age, education, and dementia severity, FTD patients performed worse overall and showed similar impairment in letter and semantic category fluency, whereas AD patients showed greater impairment in semantic category than letter fluency. A measure of the disparity between letter and semantic category fluency (the semantic index) was effective in differentiating FTD from AD patients, and this disparity increased with increasing severity of dementia. These unique patterns of letter and semantic category fluency deficits may be indicative of differences in the relative contribution of frontal-lobe-mediated retrieval deficits and temporal-lobe-mediated semantic deficits in FTD and AD.

Aged↗

PubMed1993

Effects of distinctiveness, repetition and semantic priming on the recognition of face familiarity.

Three experiments are reported which provide evidence for the independence of effects of repetition from those of distinctiveness and semantic priming in the recognition of familiar faces. In Experiment 1, repetition priming is shown to be additive with face distinctiveness in a face familiarity decision task, where subjects make speeded familiarity decisions to a sequence of famous and unfamiliar faces. Experiment 2 examines the combined effects of distinctiveness and semantic priming. The results suggest that the effect of distinctiveness is additive with that of semantic priming. Experiment 3 uses a more powerful design in which effects of distinctiveness and semantic priming were assessed while all items were repeated three times during the course of the experiment. Effects of repetition and distinctiveness were again additive, as were effects of repetition and semantic priming. Distinctiveness and semantic priming were additive at 1,000 ms SOA, though appeared to interact at 250 ms SOA. The results give further evidence for the separation of the mechanisms of semantic from repetition priming, and furthermore suggest that distinctiveness operates at a different locus from those of either of the priming mechanisms.

Adult↗

PubMed1999

The deterioration of semantic memory in Alzheimer's disease.

Semantic memory impairment is a common feature of dementia of the Alzheimer type (DAT). Recent research has shown that patients with DAT are more impaired (relative to non-demented controls) in generating exemplars from a particular semantic category (e.g., animals) than words beginning with a particular letter, exhibit an altered temporal dynamic during the production of category exemplars, are impaired on confrontation naming tasks and make predominantly superordinate or semantically related errors, consistently misidentify the same objects across a variety of semantic tasks, and have alterations in multi-dimensional scaling models of their semantic network that are indicative of a loss of concepts and associations. These results are consistent with the view that Alzheimer's disease results in a breakdown in the organization and structure of semantic knowledge as neurodegeneration spreads to the association cortices that presumably store semantic representations.

Aged↗

PubMed2005

Word learning by preschoolers with specific language impairment: effect of phonological or semantic cues.

PURPOSE: This study investigated whether phonological or semantic encoding cues promoted better word learning for children with specific language impairment (SLI) and whether this treatment differentially affected children with SLI and normal language (NL). METHOD: Twenty-four preschoolers ages 4;0 (years;months) to 5;11 with SLI and 24 age- and gender-matched children with NL participated. The between-group factor was language group (NL, SLI) and within-group factors were language modality (comprehension, recognition, production) and treatment condition (phonological, semantic). Word learning was assessed during fast mapping, word learning, and post-testing with trials to criterion calculated for the number of words learned. A drawing task assessed the change in semantic representation of words. RESULTS: The SLI group comprehended more words in the semantic condition and produced more words in the phonological condition, but the NL group performed similarly in both. The NL group required significantly fewer trials than the SLI group to comprehend words in the semantic and phonological conditions and to produce words in the semantic condition, but between-group differences for production were not significant for the phonological condition. CONCLUSIONS: The results suggest that preschoolers with SLI may benefit from cues that highlight the phonological or semantic properties of words but that different cues may aid different aspects of word learning.

Analysis of Variance↗

PubMed1997

Role of left inferior prefrontal cortex in retrieval of semantic knowledge: a reevaluation.

A number of neuroimaging findings have been interpreted as evidence that the left inferior frontal gyrus (IFG) subserves retrieval of semantic knowledge. We provide a fundamentally different interpretation, that it is not retrieval of semantic knowledge per se that is associated with left IFG activity but rather selection of information among competing alternatives from semantic memory. Selection demands were varied across three semantic tasks in a single group of subjects. Functional magnetic resonance imaging signal in overlapping regions of left IFG was dependent on selection demands in all three tasks. In addition, the degree of semantic processing was varied independently of selection demands in one of the tasks. The absence of left IFG activity for this comparison counters the argument that the effects of selection can be attributed solely to variations in degree of semantic retrieval. Our findings suggest that it is selection, not retrieval, of semantic knowledge that drives activity in the left IFG.

Humans↗

PubMed2000

The effect of semantic cuing on CVLT performance in healthy participants. California Verbal Learning Test.

The California Verbal Learning Test (CVLT) is a widely used measure of verbal learning and memory; however, there is little empirical evidence about the effects of the administration procedure on the test results. The primary goal of this study was to examine the effect of the semantic cuing condition on subsequent free recall of the material. A secondary goal was to assess whether prior knowledge that the words on the list are drawn from four semantic categories would enhance recall. Participants were 154 young healthy adults. The results suggested that participants who received semantic cuing according to the standardized test instructions generated the same number of correct words on the delayed free recall of the list as did those who did not receive cuing. Cuing did, however, lead participants to use greater semantic clustering in their delayed recall of the list. Participants who were provided with information prior to learning about the semantic structure of the test did not show enhanced learning relative to those who did not receive this information. We conclude that semantic cuing on the CVLT does not substantially enhance delayed recall of the material in healthy participants, although it is quite possible that cuing would have a greater effect in patients who have poor semantic organizational skills.

Adult↗

PubMed1998

Pupillary responses evoked during verbal fluency tasks indicate semantic network dysfunction in schizophrenia.

Pupillary responses, which index task controlled processing load, were recorded during semantic and phonemic fluency tasks to examine controlled search and automatic semantic network deficits in patients with schizophrenia. Word retrieval was more impaired on semantic than on phonemic fluency, but only during the first 15 seconds of trials. Pupillary dilation was greater on phonemic than on semantic fluency in nonpsychiatric participants but was greater on semantic than on phonemic fluency in the patients, during the first 15 seconds of trials. Thus, early in semantic fluency trials, patients with schizophrenia showed poorer word retrieval and abnormally high demand for frontal lobe controlled search processes, suggesting impairments in the temporal lobe automatic semantic memory processes that normally facilitate word retrieval.

Adult↗

PubMed1999

Is semantic fluency differentially impaired in schizophrenic patients with delusions?

The study of cognitive deficits in schizophrenia has recently focused upon semantics: the study of meaning. Delusions are a plausible manifestation of abnormal semantics because by definition they involve changes in personal meaning and belief. A symptom-based approach was used to investigate semantic and phonological fluency in a group of schizophrenic patients subdivided into those with delusions and those with no current delusions. The results demonstrated that deluded patients only were differentially impaired on a test of semantic fluency in comparison to phonological fluency. All subjects showed the same decline in performance over the time course of both tests indicating that retrieval speed in schizophrenia is no different from that of normal controls. Further analysis of word associations in two semantic categories (animals and body parts), revealed that deluded subjects have a more idiosyncratic organisation for animals. The findings of reduced semantic fluency production and poor logical word associations may represent a disorganised storage of semantic information in deluded patients, which in turn affects efficient access.

Adult↗

PubMed2003

Semantic and cross-case identity priming in patients with Parkinson's disease.

Semantic and cross-case identity priming were investigated in nondemented patients with Parkinson's disease (PD) and controls using the Lexical Decision Task. Three conditions were administered that consisted of the presentation of prime and target word pairs. In the semantic priming condition the word pairs were semantically related (e.g., table-CHAIR), in the cross-case identity priming condition the word pairs consisted of the same word (e.g., noise-NOISE), and in the unrelated condition the word pairs were not related semantically (e.g., guns-DEEP). A fourth condition was also administered that consisted of the presentation of a prime word and a pronounceable nonword target (e.g., starved-FORVE). Participants were asked to indicate whether the target was a real word or a nonword. The prime and target were separated by either a short or long (250 ms or 1000 ms) stimulus onset asynchrony (SOA). Results indicated that PD patients displayed normal semantic priming (i.e., faster responding to the target in the semantic condition as compared to the unrelated condition) at both the short and long SOA. Similarly, PD patients displayed normal cross-case identity priming (i.e., faster responding to the target in the identity condition relative to the unrelated condition) at the long SOA. At the short SOA, however, PD patients displayed hyper identity priming relative to controls (134 ms vs. 50 ms). These results suggest that semantic processes are normal in nondemented PD patients but that the processes involved in accessing lexical information may be overly activated in these patients.

Aged↗