Structure and Deterioration of Semantic Memory: A Neuropsychological and Computational Investigation.

Abstract

Wernicke (1900, as cited in G. H. Eggert, 1977) suggested that semantic knowledge arises from the interaction of perceptual representations of objects and words. The authors present a parallel distributed processing implementation of this theory, in which semantic representations emerge from mechanisms that acquire the mappings between visual representations of objects and their verbal descriptions. To test the theory, they trained the model to associate names, verbal descriptions, and visual representations of objects. When its inputs and outputs are constructed to capture aspects of structure apparent in attribute-norming experiments, the model provides an intuitive account of semantic task performance. The authors then used the model to understand the structure of impaired performance in patients with selective and progressive impairments of conceptual knowledge. Data from 4 well-known semantic tasks revealed consistent patterns that find a ready explanation in the model. The relationship between the model and related theories of semantic representation is discussed.

Verb acquisition and representation in Alzheimer's disease

“…One consequence of this relates to the ability to compensate for disease progression by borrowing shared features from overlapping concepts that are less degraded. A distributed semantic network for nouns thus declines relatively slowly because the well-organized hierarchical structure of these semantic networks facilitates sharing of features with overlapping concepts (Gonnerman, Andersen, Devlin, Kempler, & Seidenberg, 1997;Rogers et al, 2004). By comparison, verbs are less well-organized and may be more vulnerable to the consequences of progressive disease that degrades semantic representations.…”

“…There are several consequences of this kind of difference. A well organized hierarchical structure appears to provide strong support for compensatory mechanisms as a distributed network for noun meaning degrades during the course of the disease (Rogers et al, 2004), but similar compensation may not be as available to support processing of verbs White-Devine et al, 1996;Yi et al, 2006). Secondly, a verb represents many different types of linguistic information.…”

Semantic Cognition: A Re-examination of the Recurrent Network "Hub" Model

“…The hub model developed by Rogers et al (2004), and then extended in Lambon Ralph et al (2007), is one of the most complete models of human semantic deficits, boasting both an account of semantic dementia, a global semantic memory disorder, and herpes simplex virus encephalitis, a cause of intra-semantic deficits. This paper reports results derived from an attempted reimplementation of the hub model, performed initially as a step towards extending the model and underlying theoretical framework to provide an account for additional semantic disorders.…”

“…However sophisticated attempts to account for the deficits of some of the patient populations have been made, such as the Rogers et al (2004) model. This model proposes that a central amodal semantic "hub" is reciprocally linked to modalityspecific "spokes", which themselves extend into so-called modal pathways.…”

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AbstractThis paper explores a model of "semantic cognition" first described in Rogers et al (2004). This model was shown to reproduce the behaviour of neurological patients who perform poorly on a variety of tests of semantic knowledge; thus purporting to provide a comprehensive explanation for semantic deficits as found in patients with semantic dementia and, as extended in Lambon Ralph, Lowe, and Rogers (2007), individuals with herpes simplex virus encephalitis.

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