This thesis examines the various approaches which have been taken to investigate the concrete/abstract word distinction both in normal subjects and in patients who, as a result of brain damage, have an impairment of lexical semantic representations. The nature of the definition task as a tool for assessing the semantic representations of concrete and abstract terms was examined. It was found that definitions for abstract words differed from those of concrete words only in style, not in semantic content. The metalinguistic demands of the definition task therefore make it inappropriate for assessing the semantic representations of concrete and abstract terms in patients with any form of language impairment. The performance of four patients with semantic impairments was examined using a variety of tasks designed to assess concrete and abstract word comprehension. While some of the data can be accommodated within the framework of several theories, no single theory can adequately account for the patterns of performance in all four patients. An alternative model of semantic memory is therefore proposed in which concreteness and frequency interact at the semantic level. Jones' Ease of Predication Hypothesis, which states that the difference between concrete and abstract terms can be explained in terms of disproportionate numbers of underlying semantic features (or "predicates") was also investigated. It was found that the ease of predication variable does not accurately reflect either predicate or feature distributions, and is simply another index of concreteness. As such, the validity of this concept as the basis of theories of semantic representation should be questioned. Models based on the assumption of a "richer" semantic representation for concrete words (e.g.: Plaut & Shallice, 1993) are therefore undermined by these data. The possibility that concrete and abstract concepts can be accessed from their most salient predicates and/or features was examined in a series of semantic priming experiments. It was concluded that it is not possible to prime either concrete or abstract concepts from their constituent parts. Significant facilitation only occurred for items in which the prime and target were synonymous and therefore map onto concepts which share almost identical semantic representations. In summary, it is apparent that no current theory of semantic representation can adequately account for the range of findings with regard to the concrete/abstract word distinction. The most plausible account is some form of distributed connectionist model. However, such models are based on unsubstantiated assumptions about the nature of abstract word representations in the semantic network. Alternative proposals are therefore discussed.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:267987 |
| Date | January 1997 |
| Creators | De Mornay Davies, Paul |
| Publisher | Royal Holloway, University of London |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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