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PubMed2000

The relative time course of semantic and phonological activation in reading Chinese.

The relative time course of semantic and phonological activation was investigated in the context of whether phonology mediates access to lexical representations in reading Chinese. Compound words (Experiment 1) and single-character words (Experiments 2 and 3) were preceded by semantic and phonological primes. Strong semantic priming effects were found at both short (57 ms) and long (200 ms) stimulus onset asynchrony (SOA), but phonological effects were either absent in lexical decision (Experiment 1), were present only at the longer SOA in character decision (Experiment 2) or were equally strong as semantic effects in naming (Experiment 3). Experiment 4 revealed facilitatory or inhibitory effects, depending on SOA, in phonological judgments to character pairs that were not phonologically but semantically related. It was concluded that, in reading Chinese, semantic information in the lexicon is activated at least as early and just as strongly as phonological information.

Adult↗

PubMed1989

Semantic memory in Alzheimer's disease.

Patients with Alzheimer's disease have been suggested to have a semantic memory impairment not present in the normal old. This article reviews the performance of Alzheimer patients on tests of various aspects of semantic memory, including word finding, knowledge of the semantic attributes, and associates of concepts, as well as their category membership. The effect that semantic context has on cognitive processes such as lexical and semantic priming and memory encoding is also reviewed. Finally, the ability of theoretical constructs such as implicit memory and automaticity to explain intertask variability in Alzheimer patients' semantic performance is discussed.

Aged↗

PubMed2003

False recognition of abstract versus common objects in older and younger adults: testing the semantic categorization account.

Older adults often demonstrate higher levels of false recognition than do younger adults. However, in experiments using novel shapes without preexisting semantic representations, this age-related elevation in false recognition was found to be greatly attenuated. Two experiments tested a semantic categorization account of these findings, examining whether older adults show especially heightened false recognition if the stimuli have preexisting semantic representations, such that semantic category information attenuates or truncates the encoding or retrieval of item-specific perceptual information. In Experiment 1, ambiguous shapes were presented with or without disambiguating semantic labels. Older adults showed higher false recognition when labels were present but not when labels were never presented. In Experiment 2, older adults showed higher false recognition for concrete but not abstract objects. The semantic categorization account was supported.

Adolescent↗

PubMed2005

Memory for narrative and expository text: independent influences of semantic associations and text organization.

The author examined memory for text in terms of the independent influences of semantic knowledge associations and text organization. Semantic associations were operationalized as the semantic relatedness between individual text concepts and the text as a whole and assessed with latent semantic analysis. The author assessed text organization by simulating comprehension with the construction integration model. Text organization consistently accounted for unique variance in recall. Semantic associations strongly predicted expository recall and predicted narrative recall significantly but to a lesser extent, even when the familiarity of the narrative content was manipulated. Results suggest that prior semantic associations and novel associations in the text structure influence memory independently, and that these influences can be affected by text genre.

Association↗

PubMed2005

Unconscious primes activate motor codes through semantics.

Today, it is generally accepted that unconscious stimuli can activate a response code, which leads to a response congruency effect (RCE) on a subsequent target. However, it is not yet clear whether this is due to the semantic processing of the primes or to the formation of direct stimulus-response (S-R) associations bypassing the semantic system. Recently, it was shown that even novel primes, for which no direct S-R links exist, can also evoke an RCE that is in line with the activation of response codes through semantics. In these experiments, the authors examined 3 alternatives for this RCE from novel primes and report a novel effect in unconscious priming. First, the authors show that this effect is not limited to a small set of numerical stimuli but also extends to letter stimuli (Experiments 1-3). Second, the authors show that the RCE is not a side effect of the prime-target distance effect, as has been reported before (Experiments 1-2). Third, the authors found that, for RCE to occur, overlap at the motor level but not at the semantic level was crucial (Experiments 2-3). Finally, in addition, the results showed a category match priming effect independent of RCE. This last result is evidence that novel unconscious primes activate their semantic category prior to the target and might be considered a good marker for semantic processing.

Humans↗

PubMed2005

New semantic learning and generalization in a patient with amnesia.

New learning of semantic information is impaired in amnesia. Several reports have demonstrated that "errorless" learning techniques have allowed patients with amnesia to acquire at least some form of new semantic information, although this information appears to be relatively inflexible. Using insights and principles from connectionist modeling of cortical and medial temporal lobe memory systems, the authors describe why errorless learning procedures act as a poor proxy for the medial temporal lobe, suggesting that they artificially eliminate the variability that defines semantic information. The authors trained a patient with severe amnesia on new semantic sentences both with and without variance and then tested him on both repeated and related novel sentences to assess generalization. He successfully learned new semantic information in both conditions but demonstrated better generalization of semantic concepts following training with variance.

Aged↗

PubMed2006

Semantic memory in Alzheimer's disease and the frontotemporal dementias: a longitudinal study of 236 patients.

Using semantic dementia (SD) as a reference point, the authors assessed semantic memory in four other neurodegenerative disorders: progressive nonfluent aphasia (PNFA), frontal variant frontotemporal dementia (fvFTD), Alzheimer's disease (AD), and posterior cortical atrophy (PCA). Individuals with SD were more impaired than other groups on semantic measures and showed a characteristic pattern across tasks: category fluency (CF) worse than letter fluency (LF), naming worse than comprehension, and visual and verbal comprehension equally affected, suggesting disruption to an amodal semantic system. Individuals with AD demonstrated a similar pattern to a milder degree. Although PNFA, fvFTD, and PCA groups had abnormal scores (relative to controls) on most semantic measures, their differing patterns across measures indicate that the apparent semantic impairment in these conditions is largely secondary to other factors.

Aged↗

PubMed2003

Letter and semantic fluency in older adults: effects of mild depressive symptoms and age-stratified normative data.

Depression induced cognitive impairment, also referred to as the dementia syndrome of depression or pseudodementia, has been well characterized, yet the extent to which the more common mild depressive symptoms influence cognition has not been well studied. We sought to identify the influence of mild depressive symptoms on verbal fluency performance in a large sample of healthy community dwelling older adults. Letter and semantic fluency testing was conducted on 188 participants (ages 60-92 years) with no known history of neurologic or psychiatric disease. Depressive symptoms were assessed with the Geriatric Depression Scale (GDS). A total of 39 subjects obtained GDS scores consistent with mild depressive symptoms (GDS=10-19), and 149 subjects were identified as not depressed (GDS<10). ANOVA indicated that subjects with mild depressive symptoms performed significantly worse than normal controls on letter fluency (p<.05), but there was no significant difference between the groups on semantic fluency. Analysis of the nondepressed group stratified into young-old, middle-old, and oldest-old revealed a significant decline in semantic (p<.001) but not letter fluency with age. The nondepressed young-old showed the expected advantage for word list generation to semantic as compared to letter categories, yet this pattern was reversed in the older age groups, where letter fluency scores exceeded semantic fluency scores. Our results suggest that the presence of even mild depressive symptoms may confound using letter versus category discrepancies in the differential diagnosis of dementia. Further, our findings suggest that the commonly used strategy of examining letter-semantic fluency discrepancies may not be relevant for individuals of advanced age. Age-stratified normative data for fluency testing in older adults is also provided.

Age Factors↗

PubMed2004

The effects of literacy and education on the quantitative and qualitative aspects of semantic verbal fluency.

Semantic verbal fluency tasks are commonly used in neuropsychological assessment. Investigations of the influence of level of literacy have not yielded consistent results in the literature. This prompted us to investigate the ecological relevance of task specifics, in particular, the choice of semantic criteria used. Two groups of literate and illiterate subjects were compared on two verbal fluency tasks using different semantic criteria. The performance on a food criterion (supermarket fluency task), considered more ecologically relevant for the two literacy groups, and an animal criterion (animal fluency task) were compared. The data were analysed using both quantitative and qualitative measures. The quantitative analysis indicated that the two literacy groups performed equally well on the supermarket fluency task. In contrast, results differed significantly during the animal fluency task. The qualitative analyses indicated differences between groups related to the strategies used, especially with respect to the animal fluency task. The overall results suggest that there is not a substantial difference between literate and illiterate subjects related to the fundamental workings of semantic memory. However, there is indication that the content of semantic memory reflects differences in shared cultural background--in other words, formal education--, as indicated by the significant interaction between level of literacy and semantic criterion.

Aged↗

PubMed2002

Semantic priming in number naming.

The issue of semantic and non-semantic conversion routes for numerals is still debated in numerical cognition. We report two number-naming experiments in which the target numerals were preceded by another numeral (prime). The primes and targets could be presented either in arabic (digit) notation or in verbal (alphabetical) notation. The results reveal a semantically related distance effect: Latencies are fastest when the prime has the same value as the target and increase when the distance between prime and target increases. We argue that the present results are congruent with the idea that the numerals make access to an ordered semantic number line common to all notations, as the results are the same for within-notation priming (arabic-arabic or verbal-verbal) and between-notations priming (arabic-verbal or verbal-arabic). The present results also point to a rapid involvement of semantics in the naming of numerals, also when the numerals are words. As such, they are in line with recent claims of rapid semantic mediation in word naming.

Female↗

PubMed2002

The locus of semantic priming effects in person recognition.

Semantic priming in person recognition has been studied extensively. In a typical experiment, participants are asked to make a familiarity decision to target items that have been immediately preceded by related or unrelated primes. Facilitation is usually observed from related primes, and this priming is equivalent across stimulus domains (i.e., faces and names prime one another equally). Structural models of face recognition (e.g., IAC: Burton, Bruce, & Johnston, 1990) accommodate these effects by proposing a level of person identity nodes (PINs) at which recognition routes converge, and which allow access to a common pool of semantics. We present three experiments that examine semantic priming for different decisions. Priming for a semantic decision (e.g., British/American?) shows exactly the same pattern that is normally observed for a familiarity decision. The pattern is equivalent for name and face recognition. However, no semantic priming is observed when participants are asked to make a sex decision. These results constrain future models of face processing and are discussed with reference to current theories of semantic priming.

Adult↗

PubMed2005

Age-related declines in context maintenance and semantic short-term memory.

This study reports age-related declines in context maintenance (Braver et al., 2001) and semantic short-term memory (STM) and evidencc for a relation between the two. A group of younger and older adults completed a context maintenance task (AX-CPT), a semantically oriented STM task (conceptual span), a phonologically oriented STM task (digit span), and a meaning integration task (semantic anomaly judgement). In the AX-CPT task, a target response is required to the probe letter "X" but only when it is preceded by the letter "A" (the context). Either three (short interference) or six distractor letters (long interference) were presented between the cue and the probe. Results indicated an age-related deficit in context maintenance. Age-related declines were also observed for conceptual span and semantic anomaly judgement but not for digit span. Context maintenance was correlated with conceptual span and semantic anomaly judgement but not with digit span. These correlations were largely mediated by age differences, which also explained variance that was unique to (and not shared among) context maintenance, conceptual span, and semantic anomaly judgement.

Adult↗

PubMedDate not supplied

Differential age effects in semantic and episodic memory, Part II: Slope and intercept analyses.

This study tested for dissociations between age-related slowing in peripheral and central processes across semantic and episodic memory tasks. We report the mixed-model analysis of variance (ANOVA) results using reaction time (RT), error, and data from four different experimental tasks and eight data sets (the four tasks involved either multiple sessions or different stimuli) conducted on the same 80 participants (40 younger and 40 older adults). An earlier paper (Allen, Sliwinski, Bowie, & Madden, in press) reported the factor analysis and structural equation modeling results of this study. We employed two semantic memory tasks (lexical decision and multiplication verification) using data from two different sessions (for a total of four semantic data sets), and two episodic memory tasks (hybrid visual search and memory search with digits and with words as stimuli). For RT analyses, we found Age x Task interactions for all four episodic memory data sets, but no Age x Task interactions for the four semantic memory data sets. Also, the intercept (assumed to index peripheral processes) and slope (assumed to index central processes) analyses demonstrated that older adults (relative to younger adults) showed both intercept and slope decrements for episodic memory tasks, but only intercept decrements for semantic memory tasks. These data are consistent with a theoretical framework in which there are age-related dissociations between peripheral and central processes across semantic and episodic memory.

Adolescent↗

PubMed2004

Simulating episodic memory deficits in semantic dementia with the TraceLink model.

Although semantic dementia is primarily characterised by deficits in semantic memory, episodic memory is also impaired. Patients show poor recall of old autobiographical and semantic memories, with better retrieval of recent experiences; they can form new memories, and normal performance on pictorial recognition memory has been demonstrated. As these abnormalities in episodic memory are virtually a mirror image of those seen in the amnesic syndromes, semantic dementia poses a challenge to extant models of remote memory and amnesia. Here, we show that one such model, TraceLink, can reproduce some of the principal findings on episodic memory in semantic dementia. A loss of nodes and connections within the trace system, which can be identified with the temporal neocortical memory storage sites implicated in semantic dementia, simulates without further assumptions the findings reported above.

Amnesia↗

PubMed2000

Semiotes: a semantics for sharing.

MOTIVATION: Reliable, automated communication of biological information requires methods to declare the information's semantics. In this paper I describe an approach to semantic declaration intended to permit independent, distributed databases, algorithms, and servers to exchange and process requests for information and computations without requiring coordination or agreement among them on universe of discourse, data model, schema, or implementation. RESULTS: This approach uses Glossa, a formal language defining the semantics of biological ideas, information, and algorithms, to executably define the semantics of complex ideas and computations by constructs of semiotes, terms which axiomatically define very simple notions. A database or algorithm wishing to exchange information or computations maintains a set of mappings between its particular notions and semiotes, and a parser to translate between its indigenous ideas and implementation and the semiotes. Requests from other databases or algorithms are issued as semiotic messages, locally interpreted and processed, and the results returned as semiotes to the requesting entity. Thus, semiotes serve as a shared, abstract layer of definitions which can be computably combined by each database or algorithm according to its own needs and ideas. By combining the explicit declaration of semantics with the computation of the semantics of complex ideas, Glossa and its semiotes permit independent computational entities to lightly federate their capabilities as desired while maintaining their unique perspectives on both scientific and technical questions.

Algorithms↗

PubMed2000

The role of conceptual knowledge in object use evidence from semantic dementia.

It has been reported that patients with semantic dementia function well in everyday life and sometimes show striking preservation of the ability to use objects, even those specific objects for which the patient has degraded conceptual information. To explore this phenomenon in nine cases of semantic dementia, we designed a set of semantic tests regarding 20 everyday objects and compared performance on these with the patients' ability to demonstrate the correct use of the same items. We also administered a test of mechanical problem solving utilizing novel tools, on which the patients had completely normal ability. All but the mildest affected patient showed significant deficits of naming and on the visually based semantic matching tasks. Object use was markedly impaired and, most importantly, correlated strongly with naming and semantic knowledge. In a small number of instances, there was appropriate use of an object for which the patient's knowledge on the semantic matching tasks was no better than chance; but this typically applied to objects with a rather obvious relationship between appearance and use, or was achieved by trial and error. The results suggest that object use is heavily dependent upon object-specific conceptual knowledge, supplemented to some degree by a combination of visual affordances and mechanical problem solving.

Aphasia, Primary Progressive↗

PubMed2003

Neural basis for semantic memory difficulty in Alzheimer's disease: an fMRI study.

Patients with probable Alzheimer's disease are thought to have a semantic memory deficit. We used functional MRI to evaluate the neural basis for impaired semantic memory for ANIMALS and IMPLEMENTS in 11 patients with Alzheimer's disease and 16 healthy seniors. For both categories of knowledge, Alzheimer's disease patients show reduced activation in the left posterolateral temporal-inferior parietal cortex compared with healthy seniors. Activation changes in this heteromodal association region may be related to an impairment of the category-neutral semantic processes involved in integrating feature knowledge that is represented in modality-specific association cortices. We also found increased activation of an area of the left temporal cortex for both categories of knowledge in Alzheimer's disease that was not activated in healthy seniors. Category-specific changes were also seen in Alzheimer's disease compared with healthy seniors that may be related to the neural representation of category-specific feature knowledge represented in semantic memory. For ANIMALS, the left ventral temporal cortex was activated in Alzheimer's disease in an anatomical distribution that was posterior to the left ventral recruitment for this category in healthy seniors. For IMPLEMENTS, frontal-striatal regions were activated in Alzheimer's disease in a manner that was displaced from the locus of recruitment for this category in healthy seniors. Our findings are consistent with a two-component model of semantic memory involving category-neutral processes operating on category- specific knowledge, and both components appear to be compromised in Alzheimer's disease. Components of the large-scale neural network underlying semantic memory may modify themselves to maintain performance in the face of a neurodegenerative disease.

Aged↗

PubMed2000

Segregating semantic and syntactic aspects of processing in the human brain: an fMRI investigation of different word types.

The processing of single words that varied in their semantic (concrete/abstract word) and syntactic (content/function word) status was investigated under different task demands (semantic/ syntactic task) in an event-related functional magnetic resonance imaging experiment. Task demands to a large degree determined which subparts of the neuronal network supporting word processing were activated. Semantic task demands selectively activated the left pars triangularis of the inferior frontal gyrus (BA 45) and the posterior part of the left middle/superior temporal gyrus (BA 21/22/37). In contrast, syntactic processing requirements led to an increased activation in the inferior tip of the left frontal operculum (BA 44) and the cortex lining the junction of the inferior frontal and inferior precentral sulcus (BA 44/6). Moreover, for these latter areas a word class by concreteness interaction was observed when a syntactic judgement was required. This interaction can be interpreted as a prototypicality effect: non-prototypical members of a word class, i.e. concrete function words and abstract content words, showed a larger activation than prototypical members, i.e. abstract function words and concrete content words. The combined data suggest that the activation pattern underlying word processing is predicted neither by syntactic class nor semantic concreteness but, rather, by task demands focusing either on semantic or syntactic aspects. Thus, our findings that semantic and syntactic aspects of processing are both functionally distinct and involve different subparts of the neuronal network underlying word processing support a domain-specific organization of the language system.

Adult↗