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PubMed2006

Re-visiting "semantic facilitation" of word retrieval for people with aphasia: facilitation yes but semantic no.

Previous research has shown that word-to-picture matching for targets that cannot be named at pre-test results in improved naming relative to untreated control items for people with aphasia. This paper replicates and extends this finding and investigates its source. Is the effect a result of priming of semantic representations, or of post-semantic mechanisms in word retrieval? The first experiment shows that word-to-picture matching with unrelated distractors improves naming at short (2-3 minutes) and long (up to 25 minute) lags. There was no effect of being made aware of the relationship between word-to-picture matching and picture naming. People who have a semantic impairment improve only with a short lag between word-to-picture matching and naming. Participants with less semantic impairment show larger priming effects that are equal at short and long lags between word-to-picture matching and naming. The second experiment shows that the facilitation effect is just as large for word-to-picture matching with unrelated distractors as with semantically-related distractors. Furthermore, overall there was no difference between matching with coordinate items and with associated items. The results of these experiments show that facilitation of naming by word-to-picture matching in people with aphasia cannot be a result of the priming of semantic representations. Instead they are consistent with two effects: word-to-picture matching results in priming at a lemma level for aphasic people with a semantic impairment that is only found with a short lag between word-to-picture matching and naming. Word-to-picture matching causes priming of the lemma to output lexicon entry mapping that benefits participants with less semantic impairment that is evident at both a short and long lag between word-to-picture matching and naming. These findings fit well with previous research on repetition priming of naming with normal subjects.

Aphasia↗
PubMed2000

Visual semantic features are activated during the processing of concrete words: event-related potential evidence for perceptual semantic priming.

There has been conflicting evidence to date regarding the existence of non-strategic semantic priming based on semantic similarity, and in particular on visual-perceptual semantic features (e.g., button-coin: words refer to objects with the same global shape). Both event-related potential (ERP) and reaction time (RT) measures were employed to investigate visual-perceptual semantic priming in a word-pair lexical decision task designed to minimise the contribution of conscious strategic processing. While no RT priming effect was observed, a robust priming effect was obtained on the N400 component of the ERP. This result shows that semantic priming, as indexed by the N400 component, can be supported by nonassociative visual-perceptual semantic relations. The data are consistent with perceptual form information being accessed during the processing of concrete words, and provide support for models of semantic representation which incorporate semantic features and form information.

Adult↗
PubMed2005

Failing to get the gist: reduced false recognition of semantic associates in semantic dementia.

In 2 experiments involving patients with semantic dementia, the authors investigated the impact of semantic memory loss on both true and false recognition. Experiment 1 involved recognition memory for categories of everyday objects that shared a predominantly semantic relationship. The patients showed preserved item-specific recollection for the pictorial stimuli but, compared with control participants, exhibited significantly reduced utilization of gist information regarding the categories of objects. The latter result is consistent with the patients' degraded semantic knowledge. Experiment 2 involved categories of abstract objects that were related to one another perceptually rather than semantically. Patients with semantic dementia obtained item-specific recollection and gist memory scores that were indistinguishable from those of control participants. These results suggest that the reduction in gist memory in semantic dementia is largely specific to semantic representations and cannot be attributed to general difficulty with abstracting and/or utilizing gistlike commonalities between stimuli.

Aged↗
PubMed2000

Semantic priming in the prime task effect: evidence of automatic semantic processing of distractors.

The automaticity of the semantic processing of words has been questioned because of the reduction of semantic priming when the prime word is processed nonsemantically--for example, in letter search (the prime task effect). In two experiments, prime distractor words produced semantic priming in a subsequent lexical decision task, but with the direction of priming (positive or negative) depending on the prime task. Lexico-semantic tasks produced negative semantic priming, whereas letter search produced positive semantic priming. These results are discussed in terms of task-based inhibition. We argue that, given the results from the distractors, the absence of semantic priming does not indicate an absence of semantic activation but reflects the action of control processes on prepotent responses when less practiced responses are needed.

Adult↗
PubMed2006

Connectivity among semantic associates: an fMRI study of semantic priming.

Semantic priming refers to a reduction in the reaction time to identify or make a judgment about a stimulus that has been immediately preceded by a semantically related word or picture and is thought to result from a partial overlap in the semantic associates of the two words. A semantic priming lexical decision task using spoken words was presented in event-related fMRI and behavioral paradigms. Word pairs varied in terms of semantic relatedness and the connectivity between associates. Thirteen right-handed subjects underwent fMRI imaging and 10 additional subjects were tested in a behavioral version of the semantic priming task. It was hypothesized priming would be greatest, reaction time fastest, and cortical activation reduced the most for related word pairs of high connectivity, followed by related word pairs of low connectivity, and then by unrelated word pairs. Behavioral and fMRI results confirmed these predictions. fMRI activity located primarily in bilateral posterior superior and middle temporal regions showed modulation by connectivity and relatedness. The results suggest that these regions are involved in semantic processing.

Adult↗
PubMed2005

The role of semantic distance in category-specific impairments for living things: evidence from a case of semantic dementia.

In this paper, we describe a patient (LI) suffering from semantic dementia who showed a category-specific naming impairment for living things over and above the effects of several nonsemantic confounding variables. We investigated the characteristics of LI's impairment to address the following three issues raised in three different accounts of category-specific impairments: (i) the role of an imbalance in the loss of sensory compared to nonsensory features (assumed by the Sensory Functional Theory [Warrington, E. K., & Shallice, T. (1984). Category-specific semantic impairments. Brain, 107, 829-859]); (ii) the role of cross domain differences in Feature Correlation (assumed by the Conceptual Structure Account [Moss, H., Tyler, L. K., & Devlin, J. T. (2002). The emergence of category-specific deficits in a distributed semantic system. In: E. M. E. Forde & G. W. Humphreys (Eds.), Category Specificity in Brain and Mind (pp. 115-147). New York: Psychology Press]); (iii) the role of semantic distance (proposed by Cree and McRae [Cree, G. S., & McRae, K. (2003). Analyzing the factors underlying the structure and computation of the meaning of chipmunk, cherry, chisel, cheese, and cello (and many other such concrete nouns). Journal of Experimental Psychology: General, 132, 163-201]). We found that semantic distance was the only factor causally linked to LI's poorer performance on living things. In fact, her naming performance was less accurate on items that had many semantic neighbours, which is typical of living things. On the contrary, a feature listing task revealed that the features available to LI were not predicted by their level of correlation, as expected by the Conceptual Structure Account. Finally, at variance with the Sensory Functional Theory, although LI quoted sensory features less accurately than nonsensory ones, this did not give rise to a disproportionate loss of semantic features in the living domain.

Anomia↗
PubMed2003

Anomia for people names in DAT--evidence for semantic and post-semantic impairments.

Proper name anomia is a frequent finding among patients in the early stages of Alzheimer's disease. The present study investigates naming of famous persons in a group of DAT patients, a group of persons with mild cognitive impairment (MCI) and healthy controls. The study is aimed at distinguishing the relative contributions of semantic and post-semantic factors to difficulties in proper name retrieval. As shown by a significantly lower score in answering semantic questions, DAT patients retrieve less biographical knowledge related to famous persons than healthy elderly subjects and persons with mild cognitive impairment. This finding is in line with the frequent observation of semantic deficits in early and moderate DAT. The high number of Tip-of-the-Tongue (TOT) answers in DAT found in relation to few spontaneously named items shows that post-semantic deficits are as important as semantic deficits in determining anomia for people names in DAT. Moreover, DAT patients were less sensitive to phonological cueing than healthy persons or persons with mild cognitive impairment. These findings suggest that proper name anomia in DAT is not only due to semantic deficits, but also to problems in accessing the phonological representation, as well as to a degradation of phonological representations. Thus, naming deficits in DAT differ not only quantitatively, but also qualitatively from the difficulties of healthy elderly persons. No significant differences were found between persons with mild cognitive impairment and healthy controls in proper name retrieval.

Aged↗
PubMed2006

Lost in semantic space: a multi-modal, non-verbal assessment of feature knowledge in semantic dementia.

A novel, non-verbal test of semantic feature knowledge is introduced, enabling subordinate knowledge of four important concept attributes--colour, sound, environmental context and motion--to be individually probed. This methodology provides more specific information than existing non-verbal semantic tests about the status of attribute knowledge relating to individual concept representations. Performance on this test of a group of 12 patients with semantic dementia (10 male, mean age: 64.4 years) correlated strongly with their scores on more conventional tests of semantic memory, such as naming and word-to-picture matching. The test's overlapping structure, in which individual concepts were probed in two, three or all four modalities, provided evidence of performance consistency on individual items between feature conditions. Group and individual analyses revealed little evidence for differential performance across the four feature conditions, though sound and colour correlated most strongly, and motion least strongly, with other semantic tasks, and patients were less accurate on the motion features of living than non-living concepts (with no such conceptual domain differences in the other conditions). The results are discussed in the context of their implications for the place of semantic dementia within the classification of progressive aphasic syndromes, and for contemporary models of semantic representation and organization.

Aged↗
PubMed2003

The effect of semantic distance in yes/no and go/no-go semantic categorization tasks.

The effect of semantic distance (Lund & Burgess, 1996) was examined in three semantic categorization experiments. Experiment 1, a yes/no task that required participants to make animal/nonanimal judgments by responding to both sets of stimuli (Forster & Shen, 1996), revealed no effect of semantic distance. Experiment 2, a go/no-go task that required participants to respond to only the experimental (i.e., nonanimal) items, revealed a large effect of semantic distance. In addition, response latencies were longer and error rates were lower to the experimental items in Experiment 2 than to those in Experiment 1. These findings were replicated in Experiment 3, in which semantic distance and task condition were manipulated within subjects. We conclude that these results are consistent with (1) the view that the go/no-go tasks elicited more extensive processing of the experimental items and (2) a connectionist account of semantic activation, whereby processing is facilitated by the presence of semantic neighbors.

Humans↗
PubMed2003

Semantic context-processing deficit in thought-disordered schizophrenic patients: evidence from new semantic priming paradigms.

INTRODUCTION: Disorders in the processing of the semantic context are now a well-established phenomenon in thought-disordered (TD) schizophrenic patients, and have been revealed especially well by studies that have made use of the experimental paradigm of lexical decision tasks coupled with semantic priming. The main question addressed by this study was the evaluation of the experimental conditions under which TD schizophrenic patients are able to deploy cognitive strategies for semantic context processing. METHODS: We studied semantic priming in two double lexical decision tasks (i.e., involving the explicit processing of the prime word) using a sequential presentation of words (stimulus onset asynchrony; SOA 500 ms) with a different proportion of related words (Experiment 1 with 25% vs. Experiment 2 with 15%) in 15 TD schizophrenic and 15 normal participants. RESULTS: The results showed no significant differences between the semantic priming of TD schizophrenic and normal participants for Experiment 1, unlike Experiment 2 in which we observed a significant reduction of the amplitude of semantic priming in TD schizophrenic patients. The results of Experiment 1 contrast with those obtained previously (Besche et al., 1997) using a classical lexical decision task (implicit processing of the prime word) which also contained 25% related words. CONCLUSIONS: Experimental variables, such as the cognitive processing required by the prime word or the proportion of related words or the way they are manipulated, all seem to influence the emergence of semantic priming abnormalities in TD schizophrenic patients.

Journal Article↗
PubMed2002

Modulation of the lexical-semantic network by auditory semantic priming: an event-related functional MRI study.

The current event-related fMRI study specifies the neuroanatomical correlates of semantic priming and differences in semantic relation types using an auditory primed lexical decision task (LDT). Word pairs consisted of different relation types, associations (key-chain), pure categorical relations (cow-dog), and unrelated words (table-window), as well as word-pseudoword (way-tinne) and pseudoword-pseudoword (ahurn-döva) pairs. The factor lexical status, i.e., the processing of words compared to pseudowords, was associated with activation in the middle temporal gyri and the left striatum. The factor relatedness, i.e., the contrast between unrelated and related target words, was associated with increased activation of the left inferior frontal gyrus, the deep frontal operculum bilaterally, and the middle frontal gyri. A direct contrast between the two semantic relation types indicated that the processing of purely categorical compared to associative information recruits the right precuneus, the isthmus gyrus cinguli, and the cuneus, suggesting more effortful processing of the former information type. The present data show that the factors lexical status, semantic relatedness, and type of semantic relation in a primed LDT modulate the hemodynamic response in cerebral areas that subserve auditory word recognition and subsequent lexical-semantic processing.

Adult↗
PubMed1993

Associative semantic network dysfunction in thought-disordered schizophrenic patients: direct evidence from indirect semantic priming.

The characteristics of the spread of semantic activation in associative networks in normal subjects, thought-disordered (TD) and nonthought-disordered (NTD) schizophrenic patients with respect to time and semantic distance are examined. Direct and indirect semantic priming effects at two stimulus onset asynchronies (SOA) in a lexical decision task reveal that semantic associations spread further and faster in TD schizophrenic patients than in normal controls and in NTD schizophrenic patients. From a methodological point of view, indirect semantic priming at short prime-target intervals appears to be the best indicator of associative network dysfunction. The findings are discussed within the framework of current research on the effect of dopamine on the signal-to-noise ratio in cortical neural networks. Data suggest that semantic associative memory operates at a comparatively lower signal-to-noise ratio in thought-disordered schizophrenic patients.

Adolescent↗
PubMed1984

The semantic deficit in aphasia: the relationship between semantic errors in auditory comprehension and picture naming.

Thirty aphasic subjects were asked to point to pictures on auditory command both when the distractors came from the same semantic category as the target and when the distractors were unrelated to the target picture. The aphasics made significantly more semantic errors than non-aphasic brain-damaged controls; the incidence of semantic comprehension errors was unrelated to aphasic diagnostic groups but was related to the overall severity of aphasia. The subjects were subsequently asked to name the pictures from the comprehension task; pictures that had elicited semantic errors in comprehension were no less likely to be named than those that had not, but the incidence of semantic errors in comprehension correlated significantly with their incidence in naming. The implications of a semantic deficit common to both auditory comprehension and naming that is not specific to particular lexical items is discussed in relation to a number of information processing models of the lexicon.

Adolescent↗
PubMed1992

Semantic additivity and semantic inhibition: dissociable processes in the cerebral hemispheres?

We report the results of two visual half-field semantic priming experiments using a high proportion of related trials to examine hemisphere asymmetries for semantic processes beyond those attributable to automatic meaning activation. Contrary to previous investigations, we obtained inhibition for unrelated trials in both visual fields. However, priming was additive (being greater for words related via category membership and association than for either single dimension) only when words were presented to the RVF/left hemisphere. A third experiment, using centrally presented stimuli, implied that semantic additivity should be attributed to post-access meaning comparisons and inhibition to the generation of semantic expectancies. These results suggest (1) that inhibition and additivity are potentially dissociable "controlled" semantic processes and (2) that the left hemisphere predominates for meaning integration across successively presented words. The availability of finely tuned meaning integration processes in the left hemisphere may contribute to its superiority in language processing, despite right hemisphere competence for some semantic operations.

Adult↗
PubMed2002

Priming summation in the cerebral hemispheres: evidence from semantically convergent and semantically divergent primes.

The ability to activate and to maintain a large and relatively undifferentiated semantic field has been thought to be an important component of lexical semantic processing by the right hemisphere (RH). An implication of this unique propensity of the RH was examined in the present study that included two divided visual field priming experiments with SOAs of 800 and 2500 ms. The experiments investigated the ability of the RH and the left hemisphere (LH) to summate activation from multiple primes followed by a laterally presented ambiguous target word. The priming words either converged onto the same semantic representation (i.e. all three words related to either the dominant or to the subordinate meaning of the target) or diverged onto distinct semantic representations (i.e. two words related to the dominant and one to the subordinate meaning of the target, or vice versa). Results indicated that for either an 800 or 2500 ms stimulus onset asynchrony (SOA) the LH benefited most from three semantically convergent primes that converged onto the dominant meaning of the ambiguous target word. There was no facilitation when three subordinate primes preceded the target. When the primes diverged onto different meanings, there was significant facilitation for the 800 ms SOA only. In contrast, with an 800 ms SOA, the RH benefited only from semantically divergent primes, that diverged onto alternate meanings of the ambiguous target word. With a 2500 ms SOA, the RH benefited from all combinations of primes. The discussion focuses on the implications for language processing of the differences between the two hemispheres in the scope and temporal pattern of the multiple prime effect.

Adult↗
PubMed2004

The contribution of autobiographical significance to semantic memory: evidence from Alzheimer's disease, semantic dementia, and amnesia.

In a previous study [Memory Cognit., in press], we demonstrated that some semantic concepts are more likely than others to be associated with specific personal memories, and that this autobiographical significance gives these concepts special status in long-term memory. In this paper, we explore the possible neural correlates of autobiographically significant semantic knowledge and examine whether or not autobiographical significance is a factor in determining patterns of semantic memory loss caused by brain damage. Using famous names that were rated on various attributes, including autobiographical significance, by control participants in a norming study [Memory Cognit., in press], we found that semantic dementia (SD) patients were more likely to recognize, identify and remember autobiographically significant episodes involving famous names that were rated high in autobiographical significance as compared to equally familiar names that were rated low. By contrast, people with Alzheimer's disease (AD) and people with medial temporal lobe (MTL) amnesia did not exhibit this preference for names rated high in autobiographical significance. Furthermore, in tests of free recall, recognition, fame judgment and speeded reading, semantic dementia patients demonstrated a performance advantage for autobiographically significant famous names, whereas the other patient groups did not. These findings suggest a critical role for medial temporal regions in the mediation of autobiographical memory and the interaction between personal experience and semantic memory. Theoretical implications are discussed.

Adult↗
PubMed1999

Alterations in the dynamics of semantic activation in Alzheimer's disease: evidence for the Gain/Decay hypothesis of a disorder of semantic memory.

While it has been commonly assumed that a deficit in semantic memory underlies many of the clinical and cognitive features of early Alzheimer's disease (AD), there has been little agreement on what constitutes a proper theoretical description of this impaired system. Currently, most theories of this disorder fall into two categories: those that posit degraded semantic representations, and those that posit impaired retrieval operations with relatively intact semantic representations. It is argued that each position has both empirical and logical disadvantages that have prevented the development of a consensus on how to describe the pathology of semantic memory in AD. In this paper we present the details and supportive evidence for an alternative account of the semantic memory deficit of AD: the Gain/Decay hypothesis. The core claim of the Gain/Decay hypothesis is that a reduction in the time constant of spreading activation in AD produces dynamic changes in the availability of semantic representations that depend on the time frame in which this information must be accessed. The implications of this hypothesis for a range of experimental and clinical phenomena are discussed, as are possible biological correlates of the hypothesized alterations in the modulation of activation.

Aged↗
PubMedDate not supplied

The compositionality of lexical semantic representations: clues from semantic errors in object naming.

We present evidence that semantic errors in object naming can arise not only from impairment to the semantic system but also from damage to input and output processes. Although each of these levels of disruption can result in similar types of semantic errors in object naming, they have different types of consequences for performance on other lexical tasks, such as comprehension and naming to definition. We show that the analysis of the co-occurrence of semantic errors in naming with different patterns of performance in other lexical processing tasks can be used to localise the source of semantic errors in the naming process. Finally, we argue that the similarity of semantic errors in object naming, resulting from damage to different components of the naming processes by which they are activated by visual input, as well as the processes by which they activate output representations.

Agraphia↗