The structure and deterioration of semantic memory: A neuropsychological and computational investigation (original) (raw)
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Structure and Deterioration of Semantic Memory: A Neuropsychological and Computational Investigation
Psychological Review, 2004
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.
Semantic Cognition: Its Nature, Its Development, and its Neural Basis
Interest in the nature of conceptual knowledge extends back at least to the ancient Greek philosophers. In recent years, there has been a wide range of different approaches to understanding the nature of conceptual knowledge, its development, and its neural basis. In most other work, however, these issues are not all treated together. Instead, workers in philosophy, adult experimental psychology, child development, and cognitive neuroscience have pursued related questions in relative ignorance of each other's efforts. Even within cognitive neuroscience, there has been until recently a relative separation between approaches taken by neuropsychologists, who study the effects of brain disease on cognition in patients, and researchers who study the neural basis of conceptual knowledge in neurologically intact populations, using functional imaging and related methods.
Brain and Language, 1999
Nine patients with semantic dementia (the temporal lobe variant of frontotemporal dementia) were asked to define concrete concepts either from presentation of a picture of the object or from its spoken name. As expected, the patients with the most severe semantic impairment produced the least detailed definitions, and the quality of the definitions overall was significantly related to concept familiarity. Further analyses of the definitions were designed to assess two key theoretical aspects of semantic organization. (i) Do objects and their corresponding names activate conceptual information in two neuroanatomically separable (modality-specific) semantic systems? If so, then-apart from any expected commonality in performance attributable to factors such as concept familiarity-one would not predict striking item-specific similarities in a patient's picture-and word-elicited definitions. (ii) Do sensory/perceptual features and more associative/functional attributes of conceptual knowledge form two neuroanatomically separable subsystems? If so, then one would predict significant dissociations in the prominence of these two types of information in the patients' definitions. The results lead us to favor a model of the semantic system that is divided by attribute type but not by modality.
Non-verbal semantic impairment in semantic dementia
Neuropsychologia, 2000
The clinical presentation of patients with semantic dementia is dominated by anomia and poor verbal comprehension. Although a number of researchers have argued that these patients have impaired comprehension of non-verbal as well as verbal stimuli, the evidence for semantic deterioration is mainly derived from tasks that include some form of verbal input or output. Few studies have investigated semantic impairment using entirely non-verbal assessments and the few exceptions have been based on results from single cases ([3]: Breedin SD, Saran EM, Coslett HB. Reversal of the concreteness eect in a patient with semantic dementia. Cognitive Neuropsychology 1994;11:617±660, [12]: Graham KS, Becker JT, Patterson K, Hodges JR. Lost for words: a case of primary progressive aphasia? In: Parkin A, editor. Case studies in the neuropsychology of memory, East Sussex: Lawrence Erlbaum, 1997. pp. 83±110, [21]: Lambon Ralph MA, Howard D. Gogi aphasia or semantic dementia? Simulating and assessing poor verbal comprehension in a case of progressive¯uent aphasia. Cognitive Neuropsychology, (inpress).
The format of conceptual representations disrupted in semantic dementia: A position paper
Cortex, 2012
To account for the selective, progressive and multimodal conceptual disruption observed in semantic dementia (SD), Patterson et al., 2007 have proposed that the neural network for semantic memory cannot consist of a 'distributed only' system, but requires a single convergence zone or 'hub' that supports the interactive activation of representations in all modalities and for all semantic categories. This 'semantic hub' should be bilaterally supported by anterior regions of the temporal lobes (ATL) and contain amodal representations. However, anatomo-clinical data show that it is only in the moderate to advanced stages of the disease, when atrophy affects the ATL bilaterally, that the semantic impairment is 'multi-modal', whereas in its early stages, when important asymmetries can be observed at the level of the ATL, the semantic impairment can be modality-specific. In these cases, it mainly affects the lexical-semantic knowledge when the left temporal lobe is more atrophic and the pictorial representations when the atrophy prevails on the right side. In different sections of our position paper we review: (a) the lines of research suggesting that in lateralized forms of SD the semantic impairment is modality-specific; (b) other data suggesting a prevalent involvement of the left TL in verbal and of the right TL in pictorial/ sensory aspects of conceptual knowledge; (c) recent data supporting respectively the model of a bilateral amodal semantic hub and that of two lateralized, modality-specific semantic networks. Taken together, the surveyed data suggest that the semantic disorder observed in SD is due to the co-occurrence of verbal and non-verbal defects, resulting from left and right ATL atrophy and that the multimodal semantic impairment observed in advanced stages of SD is due to the joint disruption of pictorial and verbal representations, rather than to the loss of an amodal knowledge, bilaterally supported by the ATL.
2000
Prior work by Gonnerman and colleagues presented a theory of semantic processing in normal and impaired populations. Their account incorporates distributed representations and predicts a complex relationship between semantic knowledge and naming ability. According to this account, during the course of progressive brain damage, one should observe different relationships between damage to semantic knowledge and naming ability for natural kinds
It is demonstrated how a modality-specific semantic memory system can account for categoryspecific impairments after brain damage. In Experiment I, the hypothesis that visual and functional knowledge play different roles in the representation of living things and nonliving things is tested and confirmed. A parallel distributed processing model of semantic memory in which knowledge is subdivided by modality into visual and functional components is described.
Comprehension of concrete and abstract words in semantic dementia
Neuropsychology, 2009
The vast majority of brain-injured patients with semantic impairment have better comprehension of concrete than abstract words. In contrast, several patients with semantic dementia (SD), who show circumscribed atrophy of the anterior temporal lobes bilaterally, have been reported to show reverse imageability effects, i.e., relative preservation of abstract knowledge. Although these reports largely concern individual patients, some researchers have recently proposed that superior comprehension of abstract concepts is a characteristic feature of SD. This would imply that the anterior temporal lobes are particularly crucial for processing sensory aspects of semantic knowledge, which are associated with concrete not abstract concepts. However, functional neuroimaging studies of healthy participants do not unequivocally predict reverse imageability effects in SD because the temporal poles sometimes show greater activation for more abstract concepts. We examined a caseseries of eleven SD patients on a synonym judgement test that orthogonally varied the frequency and imageability of the items. All patients had higher success rates for more imageable as well as more frequent words, suggesting that (a) the anterior temporal lobes underpin semantic knowledge for both concrete and abstract concepts, (b) more imageable items -perhaps due to their richer multimodal representations -are typically more robust in the face of global semantic degradation and (c) reverse imageability effects are not a characteristic feature of SD.