PubMed Health⌕ Search

Biomedical subjects

Sebastian J Crutch

Publications and source records attributed to Sebastian J Crutch.

9 recordsLinked to original sources
PubMed2006

Qualitatively different semantic representations for abstract and concrete words: further evidence from the semantic reading errors of deep dyslexic patients.

This paper presents an investigation of the hypothesis that conceptual knowledge for abstract and concrete items is underpinned by qualitatively different representational frameworks (Crutch and Warrington, 2005a). A re-analysis of the semantic reading errors of four deep dyslexic patients is presented, examining the incidence of semantically associated and semantically similar errors in response to abstract and concrete target words. The results demonstrate that abstract target words elicit a greater proportion of associative than similar errors, while concrete words show the reverse pattern. These findings provide evidence which converges with that previously documented for a semantic refractory access dysphasic to suggest that abstract concepts are represented in an associative network while concrete concepts are represented in a categorical framework.

Adult↗
PubMed2005

Computation of tactile object properties requires the integrity of praxic skills.

We describe a series of experiments to examine the tactile identification of objects over the course of neurological recovery in a patient with an intracerebral haemorrhage involving the left inferior and superior parietal lobe. Tactile agnosia in this case involved the ipsilesional as well as the contralesional hand, allowing us to observe the effects of dominant parietal lobe damage without the confounding effects of hemiparesis. The findings demonstrate that both apraxia and tactile apperceptive agnosia may result from a unilateral lesion involving the left parietal lobe. The findings further suggest that the computation of macro-geometrical and micro-geometrical tactile object properties is dissociable. Macro-geometrical tactile analysis depends on intact programming of exploratory hand movements, while the role of such movements in micro-geometrical analysis is less clear.

Adult↗
PubMed2004

Abstract and concrete concepts have structurally different representational frameworks.

The architecture supporting our conceptual knowledge of abstract words has remained almost entirely unexplored. By contrast, a vast neuropsychological, neurolinguistic and neuroimaging literature has addressed questions relating to the structure of the semantic system underpinning our knowledge of concrete items (e.g. artefacts and animals). In the context of semantic refractory access dysphasia, a series of experiments exploring and comparing abstract and concrete word comprehension are described. We demonstrate that semantically associated abstract words reliably interfere with one another significantly more than semantically synonymous abstract words, while concrete words show the reverse pattern. We report the first evidence that abstract and concrete word meanings are based in representational systems that have qualitatively different properties. More specifically, we show that abstract concepts, but not concrete concepts, are represented in an associative neural network. Furthermore, our patient was found to have significantly greater difficulty in identifying high frequency than low frequency abstract words. This observation constitutes the first evidence of an inverse word frequency effect. Our results challenge the generality of many existing models of human conceptual knowledge, which derive their structure from experimental findings in the concrete domain alone.

Aged↗
PubMed2004

The semantic organisation of proper nouns: the case of people and brand names.

We describe the performance of a patient (AZ) with a semantic refractory access disorder on a series of experiments probing comprehension of two broad proper noun categories, namely person names and brand names. By inducing and manipulating the semantic relatedness effects which are commonly observed in semantic refractory access patients, we demonstrate that famous person knowledge is primarily organised by occupation, whilst knowledge of brands is organised by product type. For instance, we show that AZ has significantly greater difficulty identifying a famous person from among distractor personalities who have the same occupation (e.g. composers: Beethoven, Mozart, Handel, and Bach) than those who have different occupations (e.g. Beethoven, Picasso, Shakespeare, and Jefferson). We also show that such semantic relatedness effects do not occur when stimuli are grouped by another variable such as nationality. We argue that these semantic distance effects reflect the greater build-up of refractoriness among concepts which are supported by shared neural circuitry. In psychological space, it seems natural that these individuals should be classified in this way. The strength of our findings lie in the fact that this organisation of psychological space is mirrored by neural organisation. Thus, we report a previously undocumented degree of fine-grain organisation within conceptual knowledge of these classes of proper nouns. We also interpret our data as providing the strongest empirical support to date for the semantic module of cognitive models of person recognition.

Aged↗
PubMed2003

Spatial coding of semantic information: knowledge of country and city names depends on their geographical proximity.

We report the case of a patient, A.Z., with a refractory disorder of semantic processing. Using a number of spoken word-written word matching paradigms, her comprehension of the broad proper nouns category of place names was investigated. In addition to being sensitive to temporal factors, A.Z.'s ability to identify country or city names accurately was significantly worse when selecting a target from an array of geographically close rather than distant places. The influence of geographical proximity and location was observed even when identifying proximal and distal English towns, but not with less well-known American states. These close and distant effects are attributed to the build-up of refractoriness in representations with shared neural circuitry. Our findings reveal a previously undocumented level of fine-grain organization in this domain of semantic space. It is argued that information about geographical proximity cannot be encoded in purely verbal or visual terms. Consequently, we propose the existence of a separate module of spatially encoded information within conceptual knowledge.

Acoustic Stimulation↗
PubMed2003

Preservation of propositional speech in a pure anomic: the importance of an abstract vocabulary.

We describe a detailed quantitative analysis of the propositional speech of a patient, FAV, who became severely anomic following a left occipito-temporal infarction. FAV showed a selective noun retrieval deficit in naming to confrontation and from verbal description. Nonetheless, his propositional speech was fluent and content-rich. To quantify this observation, three picture description-based tasks were designed to elicit spontaneous speech. These were pictures of professional occupations, real world scenes and stylised object scenes. FAV's performance was compared and contrasted with that of 5 age- and sex-matched control subjects on a number of variables including speech production rate, volume of output, pause frequency and duration, word frequency, word concreteness and diversity of vocabulary used. FAV's propositional speech fell within the range of normal control performance on the majority of measurements of quality, quantity and fluency. Only in the narrative tasks which relied more heavily upon a concrete vocabulary, did FAV become less voluble and resort to summarising the scenes in an manner. This dissociation between virtually intact propositional speech and a severe naming deficit represents the purest case of anomia currently on record. We attribute this dissociation in part to the preservation of his ability to retrieve his abstract word vocabulary. Our account demonstrates that poor performance on standard naming tasks may be indicative of only a narrowly defined word retrieval deficit. However, we also propose the existence of a feedback circuit which guides sentence construction by providing information regarding lexical availability.

Aged↗
PubMed2002

Preserved calculation skills in a case of semantic dementia.

We present the case of a patient, BET, with a profound semantic dementia who shows a selective preservation of many aspects of number knowledge. In the context of an otherwise global loss of visual and verbal semantic knowledge, our patient demonstrates relatively intact number processing and numerical calculation in both the verbal and visual domain. More remarkably, BET is able to harness her intact calculation skills to number problem solving tasks. Our report provides further evidence that high-level non-verbal reasoning may persist in the absence of any viable language skills.

Aged↗