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PubMed1983

Visual problem solving in the absence of lexical semantics: evidence from dementia.

A case of dissociation between visual and praxic skills and linguistic, referential, and semantic skills is described in a case of dementia. Testing revealed that her visual processing was intact and that she was capable of a wide range of visually based tasks. These included copying geometric figures and block designs; matching items on the basis of number, color, or relative size, matching upper and lower case letters, sequencing numerals, orienting pictures, coins, and letters appropriately, and solving problems based on the identification of geometric patterns or on the identification of logical sequences based on pattern alternation, number, and size increases. In contrast, she was completely incapable of matching pictures on the basis of their semantic or referential meaning; similarly she had lost all comprehension of language. It was argued that this case demonstrates the capacities of a visual system cut off from all symbolic and semantic processes. When examined with other case studies this case provides information about the nature of and interaction between modality-specific perceptual processing and semantic processing, and information about the various cognitive factors involved in visual gnosis. The CT scan indicated frontal atrophy and marked anterior temporal atrophy, a pattern that is consistent with Pick's disease. The case was discussed in terms of the correlation between the pattern of observed strengths and deficits and the neurological pattern of atrophy.

Dementia↗

PubMed1989

Implicit access to semantic information.

Three experiments investigating the patient M.S.'s semantic memory are reported. Experiments 1 and 2 involved a category-membership decision task, in which M.S. was asked to determine whether a noun was a member of a specified semantic category. His performance in Experiment 1 was impaired for nouns from living categories in comparison with nouns from nonliving categories, and this impairment was especially marked for nouns of low typicality. Experiment 2 demonstrated an equivalent pattern of very poor performance to nouns of low familiarity from living categories. In Experiment 3 the effect of a category label on lexical decision was examined, using category labels as primes preceding nouns or pronounceable nonwords. Facilitation from related category label primes was found for typical and untypical members of living and nonliving semantic categories. These findings demonstrate that M.S. has impaired knowledge of the structure of living semantic categories when explicit access to this information is required (Experiments 1 and 2), but that some form of preserved category structure can be demonstrated in tasks which assess this implicitly (Experiment 3).

Agnosia↗

PubMed1990

Strategic and automatic priming of semantic memory in alcoholic Korsakoff patients.

To examine whether the organization of semantic memory is intact in alcoholic Korsakoff patients, three semantic memory tasks which do not require active search for stored information were administered to a group of Korsakoff patients and alcoholic controls. The first two tasks used a perceptual identification paradigm in which patients had to identify briefly presented targets preceded by associatively (experiment 1) or categorically (experiment 2) related primes. On both tasks, Korsakoff patients demonstrated intact priming effects. Because priming in these tasks was thought to reflect the operation of strategic processes, experiment 3 was designed to assess automatic spreading activation using a lexical decision task. Here as well, Korsakoff patients demonstrated intact priming. Taken together, these results support the view that the organization of semantic memory in Korsakoff patients has not been disrupted by their brain injury. The implications of these findings for understanding Korsakoff patients' impaired performance on semantic search tasks are discussed.

Aged↗

PubMed1991

Speed of processing within semantic memory following severe closed head injury.

This study investigated the effects of severe closed head injury (CHI) on the speed of information processing within semantic categories. The question of whether subjects were able to benefit from priming was also investigated. Survivors of severe CHI who were less than 1 year postinjury and survivors who were greater than 1 year postinjury were compared with neurologically normal matched controls utilizing a category judgement task. The results demonstrated slower processing within semantic memory for both groups of CHI patients compared to normal controls. Furthermore, individuals with CHI were able to benefit from priming to the same relative degree as control subjects. Overall, the results suggested semantic organization remains intact after severe CHI, but accessing semantic information is slowed.

Adult↗

PubMed1991

Capacity of making choices in the brain and its quantitative evaluation: an application to comprehension of incomplete sentences and semantic commitments.

The natural language processor in the brain generates information when it disambiguates words while reading a text in which information generation refers to making semantic commitments. Contextual facilitation of disambiguation of words appearing in the perturbed text that is derived from the unperturbed and natural one by deleting words randomly, lets the language processor revise the previous semantic commitments continuously. As the frequency of revising the previous semantic commitments increases, the amount of information generated by the language processor also increases. Revising previous semantic commitments in a continuous fashion is the functional property intrinsic to the language processor in the brain.

Brain↗

PubMed1993

Visual imagery and visual semantics in the cerebral hemispheres in schizophrenia.

Divided visual field tasks were given to normal subjects, and patients with schizophrenia and affective disorder, to investigate hemisphere differences in the visual processing of standardised pictorial stimuli. There were two conditions: in the first, subjects were asked to decide whether a common entity represented by a picture was living or non-living, a task involving a categorical judgement based on semantic information; a left hemisphere task. In the second condition, subjects judged whether these depictions represented entities which were bigger or smaller than a cat; a right hemisphere task requiring visual imagery to compare spatial dimensions. It was found that the patient groups, while showing slower reaction time (RT) overall, both displayed a right hemisphere (RH) advantage on the imagery task. Furthermore, the schizophrenics' RHs showed the normal relationship between closeness of size comparison and RT, additional evidence that the visual imagery mechanism is intact. However, these patients failed to show the expected left hemisphere advantage on the visual-semantic task. There was a suggestion that performance on the semantic task was related to the experience of vivid imagery in normals and visual hallucinations in the schizophrenics. The possible contribution of hemispheric imbalance in the production of visual hallucinations from a disordered semantic system is discussed.

Adult↗

PubMed1993

Indirect semantic priming in schizophrenic patients.

Schizophrenic patients and normal controls performed a lexical decision task involving the recognition of words which were preceded (primed) by either associated, indirectly associated, or non-associated words. In contrast to normal control subjects who showed no indirect semantic priming effect at an inter-stimulus interval (ISI) of 0 ms, a trend towards such an indirect semantic priming effect was found in schizophrenic patients. With a longer ISI of 500 ms, an indirect semantic priming effect was obtained in both groups. In the framework of network models of semantic memory, the results are interpreted as further evidence for an increase in activation or decrease in inhibition in the spreading of associational activation in schizophrenic patients.

Adolescent↗

PubMed2006

Hemispheric predominance assessment of phonology and semantics: a divided visual field experiment.

The aim of the present behavioural experiment was to evaluate the most lateralized among two phonological (phoneme vs. rhyme detection) and the most lateralized among two semantic ("living" vs. "edible" categorization) tasks, within the dominant hemisphere for language. The reason of addressing this question was a practical one: to evaluate the degree of the hemispheric lateralization for several language tasks, by using the divided visual presentation of stimuli, and then choose the most lateralized semantic and phonological for mapping language in patients by using fMRI in future studies. During the divided visual field experiment by using words (semantic tasks) and pseudo-words (phonological tasks) as stimuli, thirty-nine right-handed participants were examined. Our results have shown that all tasks were significantly left hemisphere lateralized. Furthermore, the rhyme was significantly more lateralized than phoneme detection and "living" was significantly more lateralized than "edible" categorization. The rhyme decision and "living" categorization will be used in future fMRI studies for assessing hemispheric predominance and cerebral substrate for semantics and phonology in patients. Our results also suggest that the characteristics of stimuli could influence the degree of the hemispheric lateralization (i.e., the emotional charge of stimuli for words and the position of the phoneme to be detected, for pseudo-words).

Adult↗

PubMed2004

Unitary vs multiple semantics: PET studies of word and picture processing.

In this paper we examine a central issue in cognitive neuroscience: are there separate conceptual representations associated with different input modalities (e.g., Paivio, 1971, 1986; Warrington & Shallice, 1984) or do inputs from different modalities converge on to the same set of representations (e.g., Caramazza, Hillis, Rapp, & Romani, 1990; Lambon Ralph, Graham, Patterson, & Hodges, 1999; Rapp, Hillis, & Caramazza, 1993)? We present an analysis of four PET studies (three semantic categorisation tasks and one lexical decision task), two of which employ words as stimuli and two of which employ pictures. Using conjunction analyses, we found robust semantic activation, common to both input modalities in anterior and medial aspects of the left fusiform gyrus, left parahippocampal and perirhinal cortices, and left inferior frontal gyrus (BA 47). There were modality-specific activations in both temporal poles (words) and occipitotemporal cortices (pictures). We propose that the temporal poles are involved in processing both words and pictures, but their engagement might be primarily determined by the level of specificity at which an object is processed. Activation in posterior temporal regions associated with picture processing most likely reflects intermediate, pre-semantic stages of visual processing. Our data are most consistent with a hierarchically structured, unitary system of semantic representations for both verbal and visual modalities, subserved by anterior regions of the inferior temporal cortex.

Adult↗

PubMed2005

Semantic processing of living and nonliving concepts across the cerebral hemispheres.

Studies of patients with category-specific semantic deficits suggest that the right and left cerebral hemispheres may be differently involved in the processing of living and nonliving domains concepts. In this study, we investigate whether there are hemisphere differences in the semantic processing of these domains in healthy volunteers. Based on the neuropsychological findings, we predicted a disadvantage for nonliving compared to living concepts in the right hemisphere. Our prediction was supported, in that semantic decisions to nonliving concepts were significantly slower and more error-prone when presented to the right hemisphere. In contrast there were no hemisphere differences for living concepts. These findings are consistent with either differential representation or processing of concepts across right and left hemispheres. However, we also found a disadvantage for nonliving things compared to living things in the left hemisphere, which is not consistent with a simple representation account. We discuss these findings in terms of qualitatively different semantic processing in right and left hemispheres within the framework of a distributed model of conceptual representation.

Adolescent↗

PubMed2006

Hemispheric differences in strong versus weak semantic priming: evidence from event-related brain potentials.

GOALS: Research with lateralized word presentation has suggested that strong ("close") and weak ("remote") semantic associates are processed differently in the left and right cerebral hemispheres [e.g., Beeman, M. j., & Chiarello, C. (1998). Complementary right- and left-hemisphere language comprehension. Current Directions in Psychological Science, 7(1), 2-8]. Recently, this hypothesis has been challenged [Coney, J. (2002). The effect of associative strength on priming in the cerebral hemispheres. Brain and Cognition, 50(2), 234-241]. We predicted that foveal presentation of strong and weak associates would elicit different patterns of hemispheric activity, as indexed by high-density event-related brain potentials (ERPs), and that source localization of the scalp potentials would help clarify the nature of hemispheric contributions to semantic organization. METHODS: 128-channel ERPs were recorded in two experiments as subjects performed a lexical decision task. Word trials were equally divided into strongly related, weakly related, and unrelated word pairs. All words were foveally presented. SOA was 800 ms in Experiment 1, and 200 ms in Experiment 2. RESULTS: Topographic analyses revealed medial frontal (MFN) and parietal (N400/LPC) effects for both strong and weak associates. Between approximately 450 and 550 ms, the magnitude of the N400/LPC effect indicated priming for both strong and weak associates over left parietal sites, while priming over right parietal sites was restricted to strongly related word pairs. During this interval, spatiotemporal source modeling showed that these scalp effects were best accounted for by ipsilateral sources in the medial temporal lobe. The observed pattern of asymmetries for strong versus weak associates is not consistent with certain proposals regarding the complementarity of right- and left-hemisphere contributions to semantics. It is, however, consistent with findings from visual half-field studies (Hasbrooke and Chiarello, 1998). We discuss the relevance of these results for theories of hemispheric asymmetry and meta-control in lexical semantic access.

Adolescent↗

PubMed2006

The morphosyntactic decomposition and semantic composition of German compound words investigated by ERPs.

In two experiments, we investigated the morphosyntactic decomposition and semantic composition of acoustically presented German compound words. A left-anterior negativity (LAN) was found in the ERP for gender incongruent, initial compound constituents although these constituents are syntactically irrelevant in German. This LAN provides online evidence for morphosyntactic decomposition. Experiment 1 showed also preliminary evidence for semantic composition, which was further investigated in Experiment 2 by comparing semantically transparent and opaque compounds. Transparent compounds elicited an increased negativity with a centroparietal maximum that occurred during the presentation of the head constituent. This negativity is suggested to reflect the semantic integration of compound constituents that is necessary after the constituents have been accessed separately.

Adolescent↗

PubMed2006

Dopaminergic modulation of semantic priming in healthy volunteers.

BACKGROUND: Semantic priming is a function related to prefrontal cortical (PFC) networks and is lateralized. There is evidence that semantic priming underlies dopaminergic modulation. It is known that the D1-receptor is more abundant in prefrontal networks; however, until now there have been no studies investigating the selective modulation of semantic priming with dopamine agonists. Furthermore, D1 receptor dysfunction has been described in schizophrenia, and patients with formal thought disorder seem to have disturbed focusing of associations and increased indirect priming. METHODS: With a subtraction design, we compared the influence of pergolide (D1/D2 agonist) with bromocriptine (D2 agonist) and placebo, in a randomized, double-blind, crossover design in 40 healthy male volunteers. Subjects performed a lateralized lexical decision task including direct and indirect related prime-target pairs (stimulus onset asynchrony = 750 msec). RESULTS: Only on pergolide a decrease of the indirect priming in the left hemisphere presentations was found. CONCLUSIONS: These findings point to a potential selective modulation of agonists with a D1 component on the focusing of semantic associations. The clinical relevance of this study is that it might help the development of therapeutic strategies for treating cognitive deficits in schizophrenia and Parkinson's disease, which are highly relevant to the functional outcome.

Adult↗

PubMed2006

Early semantic context integration and lexical access as revealed by event-related brain potentials.

A late neurophysiological response, the N400, is well known to reflect word processing and semantic context integration. Nevertheless, behavioural and neurophysiological data have demonstrated that word features and semantic sentence context influence linguistic processes already within the first 200 ms following the onset of the critical word stimulus. The lack of early word-related ERP effects in some studies might be due to large stimulus variance on relevant linguistic parameters, for example the length of written words or their frequency of usage. Here we investigated the effect of the length of words, their standardized lexical frequency and probability to occur in a given semantic context, by orthogonally varying these factors in a sentence-reading task. We found word frequency and probability to be reflected neurophysiologically already at 120 and 180 ms after written word onset. However, at these early stages frequency and probability effects were modulated by word length, as documented by significant interactions, whereas at later stages, around 300-500 ms, additive effects of these variables were found. These results indicate that semantic context integration may take place at a surprisingly early stage and near-simultaneously with the processing of information about the form of a word and its lexical properties, therefore challenging serial models of psycholinguistic information access. A methodological implication of this study is that, in order to obtain early psycholinguistic ERP effects, stimulus variance must be kept to a minimum.

Adult↗

PubMed2006

The temporal signatures of semantic and phonological activations for Chinese sublexical processing: an event-related potential study.

A large number of Chinese characters are made up by pairing a semantic radical and a phonetic radical. The phonetic radical usually gives a phonological clue for the pronunciation of the whole character but does not contribute to its meaning. Using an event-related potential (ERP) measurement, the present study was able to trace the very intricate interplay between phonological and semantic information embedded in the phonetic radical. It was found that, within the first 50 to 100 ms of perceiving the character, the semantic information of the phonetic radical was better preserved when the constituent phonetic radical provided a valid phonological clue (e.g., regular phonogram) than when it contained an invalid phonetic cue (e.g., irregular phonogram). However, no trace of semantic information from the phonetic radical was preserved after 300 ms. These ERP results detail the neuropsychological steps in reading Chinese and support the framework of the lexical constituent model.

Adult↗

PubMed2005

An ERP study of low and high relevance semantic features.

It is believed that the N400 elicited by concepts belonging to living is larger than N400 to non-living. This is considered as evidence that concepts are organized, in the brain, on the basis of categories. We conducted a feature-verification experiment where living and non-living concepts were matched for relevance of semantic features. Relevance is a measure of the contribution of semantic features to the "core" meaning of a concept. We found that when relevance is low the N400 is large. In addition, we found that when the two categories of living and non-living are equated for relevance the seemingly category effect at behavioral and neural level disappeared. In sum, N400 is sensitive, rather than to categories, to semantic features, thus showing that previously reported effects of semantic categories may arise as a consequence of the differing relevance of concepts belonging to living and non-living categories.

Adult↗

PubMed2006

Semantic priming effect during REM-sleep inertia in patients with narcolepsy.

Patients with narcolepsy-cataplexy (NC) present excessive daytime sleepiness (EDS), cataplexy and an altered architecture of nocturnal sleep, with frequent episodes of REM-sleep at sleep onset (SOREM-sleep). This altered organization of nocturnal sleep may be accompanied by some differences in the functioning of the cognitive processes involved in the access, organization and consolidation of information during sleep. This study attempts to ascertain whether the activation of semantic memory during REM-sleep, as measured using a technique of semantic priming (namely, the facilitation of the activation of strongly-related rather than weakly-related and, overall, unrelated pairs of prime-target words) is different in NC patients compared to normal subjects. A lexical decision task (LDT) was carried out twice in wakefulness (at 10a.m. and after a 24h interval) and twice in the period of sleep inertia following awakening from SOREM and 4th-cycle REM-sleep on 12 NC patients and from 1st- and 4th-cycle REM-sleep on 12 matched controls. Reaction time (RT) to target words, taken as a measure of the semantic priming effect, proved to be longer (a) in NC patients than in control subjects; (b) in the period of REM-sleep inertia than in wakefulness; (c) in the first rather than the second session; and (d) for unrelated compared to weakly-related and, overall, strongly-related prime-target pairs. RT in post-REM-sleep sessions was less impaired, compared to waking sessions, and less dependent on the associative strength of prime-target pairs in NC patients than in normal subjects. Finally, RT of NC patients, although longer than that of normal subjects in waking sessions, significantly improved in the second session, as a consequence of either the amount of exercise or the consolidation advantage provided by REM-sleep for the procedural components of the task. The whole picture suggests a greater effectiveness of the activation of semantic memory during (SO)REM-sleep in NC patients rather than in normal subjects, and overall for the organization of new and unexpected relationships (such as those between unrelated pairs) between items of information.

Adult↗

PubMed2006

Memory and metamemory for semantic information in obsessive-compulsive disorder.

Several studies have been conducted on OCD patients' memory and metamemory performance in episodic tasks. However, there is a clear lack of research addressing these issues for semantic memory (i.e., retrieval of information from long-term memory). Although findings regarding a memory deficit is somewhat equivocal, the empirical evidence clearly demonstrates that OCD patients with primarily checking compulsions show reduced confidence in their memory performance. The purpose of the present study was to investigate memory and metamemory performance of checkers in semantic memory domain. We compared checker OCD patients, non-checker OCD patients and normal controls on their ability to retrieve answers to general knowledge questions with a recall as well as a recognition test. We also investigated prospective (feeling-of-knowing (FOK)) and retrospective (confidence) metamemory judgments. Checker OCs were not poorer in retrieving semantic information from long-term memory. Neither were they less confident about their ability to remember currently unrecallable information in the future (FOK judgments) or about the accuracy of retrieved information (confidence judgments). Moreover, accuracy of metamemory judgments were comparable across groups. Overall, our results revealed that checker OCs do not show a memory or metamemory deficit when semantic memory was concerned, suggesting that any memory and metamemory deficit may be special to recently experienced materials.

Adult↗