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Objects and properties: a study of the breakdown of semantic memory.

This paper reports a study of the breakdown of semantic memory in the case of a subject with semantic dementia. The first experiment shows that the subject failed to comprehend words of low familiarity and word frequency, even though the spoken word forms were recognised as familiar. Experiments 2 and 3 showed (a) that the recall of word meanings in definition tasks did not vary with the generality of the word meaning (e.g. category, basic level, or subordinate property) but varied instead with the concept familiarity and frequency of the name; (b) that the ability to verify properties of basic-level objects was not affected by the ability to comprehend the property name, but depended instead on the degree of knowledge demonstrated for the object name in definition tasks; (c) that properties were frequently verified correctly when the object had been defined only to the superordinate level. It is argued that the results do not support the widely held view that, in general, specific information is lost first when semantic memory breaks down. The selective failure to recall specific information for some word meanings is discussed with reference to two theoretical accounts.

Agraphia↗

PubMed2004

Preserved knowledge of maps of countries: implications for the organization of semantic memory.

We describe two patients with selectively preserved knowledge of the category of countries. Following a series of cerebral infarcts, patient DB presented with severe perceptual impairment, including dense apperceptive agnosia,prosopagnosia, and topographical agnosia. Despite these deficits, he could effortlessly name countries from their outline maps. Patient WH, who suffered from semantic dementia, had severe naming and comprehension difficulties, with extremely sparse residual semantic knowledge. Remarkably, the category of countries was preserved. First, we argue that, for both patients, this category preservation occurs at a semantic level. Second, we discuss our findings in the context of three current models of category-specific effects (perceptual, ontogenetic, and evolutionary models). We argue that the perceptual model (Humphreys and colleagues) cannot easily accommodate our findings. By contrast, the ontogenetic (Warrington and colleagues) and evolutionary models (Caramazza and colleagues) can explain our findings. However, some modifications to both models are required. The ontogenetic model needs to envisage a spatial channel for the development of map knowledge, which is anatomically separate from channels of other categories of knowledge. The evolutionary model needs to envisage the possibility that some categories of knowledge, such as countries, may not be prewired, but learned during ontogenetic development.

Aged↗

PubMed2005

Presymptomatic semantic impairment in a case of fronto-temporal lobar degeneration associated with the +16 mutation in MAPT.

We describe a patient who came to neurological attention because of his at-risk status for the +16 exon 10 splice mutation in the tau gene (microtubule associated protein tau, MAPT), which had given rise to progressive behavioural disturbances in two of his siblings. The patient began to exhibit early signs of behavioural disturbance at around the age of symptom onset in both of his siblings. Although he did not spontaneously complain of difficulties in the domain of language, he met clinical, radiological and neuropsychological criteria for semantic dementia. On the assumption that his illness is mediated by the same pathological process as those of his siblings, we propose that this clinical picture represents the earliest changes of a semantic impairment - a phase of the illness that is often retrospectively described by patients and their relations, but has never previously been documented at first hand. Although typical of semantic dementia in many respects, the illness had several interesting and atypical features that emerged on detailed testing: first, he exhibited no insight into his difficulties; secondly, progression over a twelve-month interval was unusually slow; thirdly, he evinced a striking and consistent advantage for nonliving over living concepts; fourthly, a differential impairment of distinctive over shared knowledge did not emerge except when items that he could still name were compared with those for which he was anomic. Finally, the availability of post mortem pathological analysis from the brains of both of his affected siblings allowed us to attribute his illness to a specific pathological process which is considered unusual for patients with this clinical phenotype.

Case-Control Studies↗

PubMed2005

Jargon dyslexia in an individual with semantic dementia: further evidence for task-specificity in phonological output.

We report a patient with semantic dementia who demonstrated a very unusual dyslexia. He had a global loss of conceptual knowledge in the context of a fluent dysphasia and intact syntax. However, he did not have the surface dyslexia which is typical of semantic dementia; rather his reading impairment was characterized by speech production errors resulting in multiple neologisms. In a series of experiments it was established that input phonological and input orthographical processing were intact as was output phonology for naming and propositional speech. We demonstrate that our patient has a task-specific phonological deficit and we argue that reading and propositional speech rely upon dissociable phonological output systems. Thus we corroborate our earlier evidence of task-specific phonological output stores (Crutch and Warrington, 2001). We also document a greater difficulty with comprehending the written than the spoken word. We account for this pattern of performance in terms of our patient's attempting to read by the indirect phonological route, as with other semantic dementia patients, but suggest that this process is overridden by the task-specific speech production deficit.

Aged↗

PubMed2006

The different frameworks underlying abstract and concrete knowledge: evidence from a bilingual patient with a semantic refractory access dysphasia.

We report the case of a bilingual patient (IRQ) who acquired a semantic refractory access dysphasia following a middle cerebral artery stroke. In a series of spoken word-written word matching tasks, the degree of semantic similarity between target and distractor items was found to affect the accuracy of IRQ's identification of concrete but not abstract words. By contrast, the degree of semantic association between target and distractor items was found to affect response accuracy when identifying abstract but not concrete words. These results provide further corroboration for the notion that abstract concepts are supported by an associative representational network whereas concrete concepts are supported by a categorical representational framework. We also demonstrate an equivalent refractory deficit of comprehension in both English and Arabic. In addition, we provide the first documented evidence of a category-specific refractory deficit of knowledge for abstract words.

Aged↗

PubMed2001

Do people with Alzheimer's disease have a disproportionate deficit in functional knowledge? Verbal versus motoric access to semantic memory.

Healthy elderly and Alzheimer's disease (AD) volunteers participated in four conditions in which they were asked to demonstrate the function and category of a series of objects either verbally or non-verbally. When responding verbally to category judgement questions, volunteers with mild-moderate AD showed levels of performance comparable with age and IQ-matched healthy elderly, but when responding verbally to questions about an item's function, they show marked deficits. This deficit was substantially reduced, however, when they were encouraged to provide the information motorically. Healthy elderly were able to use either mode of access without difficulty. The results of this study suggest that functional semantic knowledge may not be disproportionately degraded, but that when cognitive resources are compromised, retrieval may depend more critically upon mode of access. Functional information, for example, is usually acquired by actually using the object. Verbalizing such functions would require suppressing the direct (motoric) route and accessing information in a less familiar (verbal) form. In short, for people with AD, apparent deficits in semantic knowledge may reflect deficient use of unfamiliar routes of access to the information rather than degradation of semantic knowledge per se.

Aged↗

PubMed1991

Semantic inhibition of ignored words during a figure classification task.

Two experiments investigated inhibitory processes in visual spatial attention. In particular, factors influencing the suppression of ignored visual stimuli were investigated. Subjects responded to geometric shapes while distractors were presented in the periphery. Distractors consisted of a single word, a pair of unrelated words, or a single word paired with a string of non-linguistic symbols. Semantic processing of the ignored words was measured with a subsequent lexical decision task. Test probes presented after the prime displays revealed suppression effects for words semantically related to a previously ignored word, but only for conditions in which two distractor words were presented. Suppression was not observed when the prime consisted of a single word or a single word paired with non-linguistic symbols. In Experiment 2 two different time delays between the onset of the primes and the onset of the test probes were used. At the shorter interval facilitatory priming was observed, while at longer intervals suppression was observed. The facilitation-suppression pattern suggests that ignored items are recognized before being suppressed. In summary, the results suggest the following: (1) that selectively attending does not restrict ignored items from gaining access to their semantic representations, and (2) that inhibition is an important process in determining the focus of attention. These results are discussed within a selective attention framework in which all items in a display gain access to memory representations, and attention to selected items causes competing items to be inhibited.

Attention↗

PubMed2007

Semantic numerical representation in blind subjects: the role of vision in the spatial format of the mental number line.

Does vision play a role in the elaboration of the semantic representation of small and large numerosities, notably in its spatial format? To investigate this issue, we decided to compare in the auditory modality the performance of congenitally and early blind people with that of a sighted control group, in two number comparison tasks (to 5 and to 55) and in one parity judgement task. Blind and sighted participants presented exactly the same distance and SNARC (Spatial Numerical Association of Response Codes) effects, indicating that they share the same semantic numerical representation. In consequence, our results suggest that the spatial dimension of the numerical representation is not necessarily attributable to the visual modality and that the absence of vision does not preclude the elaboration of this representation for 1-digit (Experiment 1) and 2-digit numerosities (Experiment 2). Moreover, as classical semantic numerical effects were observed in the auditory modality, the postulate of the amodal nature of the mental number line for both small and large magnitudes was reinforced.

Acoustic Stimulation↗

PubMed2000

Perceptual priming is not a necessary consequence of semantic classification of pictures.

Four experiments investigated how repetition priming of object recognition is affected by the task performed in the prime and test phases. In Experiment 1 object recognition was tested using both vocal naming and two different semantic decision tasks (whether or not objects were manufactured, and whether or not they would be found inside the house). Some aspects of the data were inconsistent with contemporary models of object recognition. Specifically, object priming was eliminated with some combinations of prime and test tasks, and there was no evidence of perceptual (as opposed to conceptual or response) priming in either semantic classification task, even though perceptual identification of the objects is required for at least one of these tasks. Experiment 2 showed that even when perceptual demands were increased by brief presentation, the inside task showed no perceptual priming. Experiment 3 showed that the inside task did not appear to be based on conceptual priming either, as it was not primed significantly when the prime decisions were made to object labels. Experiment 4 showed that visual sensitivity could be restored to the inside task following practice on the task, supporting the suggestion that a critical factor is whether the semantic category is preformed or must be computed. The results show that the visual representational processes revealed by object priming depend crucially on the task chosen.

Adult↗

PubMed2006

The Life Sciences Semantic Web is full of creeps!

The Semantic Web for the Life Sciences (SWLS), when realized, will dramatically improve our ability to conduct bioinformatics analyses using the vast and growing stores of web-accessible resources. This ability will be achieved through the widespread acceptance and application of standards for naming, representing, describing and accessing biological information. The W3C-led Semantic Web initiative has established most, if not all, of the standards and technologies needed to achieve a unified, global SWLS. Unfortunately, the bioinformatics community has, thus far, appeared reluctant to fully adopt them. Rather, we are seeing what could be described as 'semantic creep'-timid, piecemeal and ad hoc adoption of parts of standards by groups that should be stridently taking a leadership role for the community. We suggest that, at this point, the primary hindrances to the creation of the SWLS may be social rather than technological in nature, and that, like the original Web, the establishment of the SWLS will depend primarily on the will and participation of its consumers.

Computational Biology↗

PubMed1995

Issues in incorporation semantic integrity in molecular biological object-oriented databases.

Issues critical to ensuring semantic integrity in molecular biological data collections have been identified and include complexity, exceptions, missing data, changing models, holism and integration, delocalized data, interoperability and nomenclature. This combination is peculiar to biology and presents some interesting problems as a result. Little is known about semantic checking in object-oriented databases in general, but because such technology appears highly suitable for modeling biological data, it is appropriate to examine the ways in which object-oriented technology can support this functionality. It is concluded that object-oriented technology will support semantic checking even in a complex domain like biology. We propose 10 guidelines for future work including ways of treating exceptional cases and 'positioning' of constraints in a schema.

Biotechnology↗

PubMed2003

SEMEDA: ontology based semantic integration of biological databases.

MOTIVATION: Many molecular biological databases are implemented on relational Database Management Systems, which provide standard interfaces like JDBC and ODBC for data and metadata exchange. By using these interfaces, many technical problems of database integration vanish and issues related to semantics remain, e.g. the use of different terms for the same things, different names for equivalent database attributes and missing links between relevant entries in different databases. RESULTS: In this publication, principles and methods that were used to implement SEMEDA (Semantic Meta Database) are described. Database owners can use SEMEDA to provide semantically integrated access to their databases as well as to collaboratively edit and maintain ontologies and controlled vocabularies. Biologists can use SEMEDA to query the integrated databases in real time without having to know the structure or any technical details of the underlying databases. AVAILABILITY: SEMEDA is available at http://www-bm.ipk-gatersleben.de/semeda/. Database providers who intend to grant access to their databases via SEMEDA are encouraged to contact the authors.

Computational Biology↗

PubMed2005

Application of latent semantic analysis to protein remote homology detection.

MOTIVATION: Remote homology detection between protein sequences is a central problem in computational biology. The discriminative method such as the support vector machine (SVM) is one of the most effective methods. Many of the SVM-based methods focus on finding useful representations of protein sequence, using either explicit feature vector representations or kernel functions. Such representations may suffer from the peaking phenomenon in many machine-learning methods because the features are usually very large and noise data may be introduced. Based on these observations, this research focuses on feature extraction and efficient representation of protein vectors for SVM protein classification. RESULTS: In this study, a latent semantic analysis (LSA) model, which is an efficient feature extraction technique from natural language processing, has been introduced in protein remote homology detection. Several basic building blocks of protein sequences have been investigated as the 'words' of 'protein sequence language', including N-grams, patterns and motifs. Each protein sequence is taken as a 'document' that is composed of bags-of-word. The word-document matrix is constructed first. The LSA is performed on the matrix to produce the latent semantic representation vectors of protein sequences, leading to noise-removal and smart description of protein sequences. The latent semantic representation vectors are then evaluated by SVM. The method is tested on the SCOP 1.53 database. The results show that the LSA model significantly improves the performance of remote homology detection in comparison with the basic formalisms. Furthermore, the performance of this method is comparable with that of the complex kernel methods such as SVM-LA and better than that of other sequence-based methods such as PSI-BLAST and SVM-pairwise.

Algorithms↗

PubMed1979

Semantic access dyslexia.

An analytical investigation of the residual reading capacities of a single patient with dyslexia without dysgraphia is reported. Both his ability to name and to comprehend letters and words were severely impaired. The major finding of this investigation was AR's striking capacity for categorizing words he could not read. In addition there was evidence of semantic priming effects. Thus AR was frequently able to achieve partial comprehension of words he could not read. The orthodox interpretation of the dyslexia without dysgraphia in terms of a disconnection syndrome is shown to be inappropriate, at least for the present case, where the deficit appears to be within the semantic domain; it is argued that this type of dyslexia is due to an impairment in accessing semantic information.

Auditory Perception↗

PubMed1998

Category specific semantic loss in dementia of Alzheimer's type. Functional-anatomical correlations from cross-sectional analyses.

In the context of focal brain injury, selective loss of semantic knowledge in the domain of either natural kinds or artefacts is usually considered to reflect the differential importance of temporal and frontoparietal regions to the representations of perceptual and functional attributes, respectively. It is harder to account far as a feature of a more diffuse process, and previous cross-sectional analyses of patients with dementia of Alzheimer's type (DAT) have differed over whether category effects occur. In our series of 58 patients with probable DAT, we demonstrated a significant group advantage for artefacts, and explored possible reasons for the inconsistency of this finding in other studies. A multiple single-case strategy revealed not only individuals with consistent advantages for artefacts but also individuals with consistent advantages for natural kinds. By ranking the individuals according to measures of naming performance and global intellectual ability, we showed that the strength of the group advantage for artefacts was dependent on the former but not the latter variable. The findings are discussed in the context of two competing theories of semantic breakdown in DAT. One differentiates between domains of knowledge in terms of the structure of semantic representations within a single distributed network; the other emphasizes the importance of different brain regions in the category distinction. We conclude that our findings are in keeping with the predictions of the latter hypothesis.

Aged↗

PubMed2002

Can segregation within the semantic system account for category-specific deficits?

Functional neuroimaging was used to investigate the extent to which category-specific semantic deficits in patients can be accounted for in terms of the demands placed on neural systems underlying different types of semantic knowledge. Unlike previous functional imaging studies of category specificity, we used a factorial design that crossed category (tools and fruits) with tasks requiring retrieval of either action or perceptual (real life size) knowledge. The presentation of tools relative to fruit increased activation in the same left posterior middle temporal area that was linked to the retrieval of action knowledge in general (for fruit as well as tools). However, we found no correlation between activation evoked by fruit and the size retrieval task. The left medial anterior temporal cortex was the only region to be activated for fruit relative to tools. We argue that the sensory-functional theory of category-specific effects is insufficient to account for the current neuroimaging literature. However, the data do support a more refined version of the theory: tools, relative to fruit, are more strongly linked to manipulative/motor knowledge and, for some tasks, fruit may be more reliant on integrating multiple semantic features.

Adult↗

PubMed1996

Age differences in episodic memory, semantic memory, and priming: relationships to demographic, intellectual, and biological factors.

This study examined age differences in episodic memory, semantic memory, and priming using a random sample of 1,000 men and women from 10 age groups (35, 40, 45, . . . 80 years). The main purpose was to determine whether an age effect existed after differences on various demographic, intellectual, and biological factors had been controlled for. The simple correlations of age with episodic and semantic memory performance were found to be significant, whereas no relationship was found between age and levels of priming. After controlling for differences on the background factors, age predicted episodic but not semantic memory performance. It is proposed that the failure to account for the age effect on episodic memory is because it is caused by age-related neuronal changes.

Adult↗

PubMed1980

Semantic encoding in older adults as evidenced by release from proactive inhibition.

Wickens' Release from Proactive Inhibition paradigm was used to investigate semantic encoding in healthy older persons, nursing home residents, and college students. Significant PI Release effects, which did not interact with age, were obtained for taxonomic category and semantic differential dimensions. However, older persons, especially nursing home residents, displayed lower percentages of recall than college students, indicating that their semantic processing was less efficient. It was suggested that older and younger adults may differ not so much as their levels (or depth) of encoding as in their degree of elaboration within particular levels.

Adult↗