Abstract
We present a preliminary set of connectionist models of impairments to semantic memory, exploring the conditions under which double dissociations between knowledge of living and non-living entities occur. Small et al [1] argue that category specific impairments are a consequence of semantic feature based representations in a fully distributed memory system. Farah and McClelland [2] argue that category specific impairments arise due to modular structure in semantic memory, albeit structure that is specific to modality; they hypothesise that living and non-living entities have a differential reliance on perceptual and functional features. We evaluated these respective claims by lesioning a simple autoassociative model of semantic memory, using a 2x2 design: fully distributed architecture versus partially modular architecture with modality specific channels; Small et al’s training set versus a training set constructed according to Farah and McClelland’s perceptual/functional scheme. One thousand stochastic lesions were applied to each network ‘subject.’ The results supported Farah and McClelland: on average, double dissociations required modular structure and differential reliance on modalities. However, by choosing select (i.e. rare) lesions from each set of 1000, double dissociations of living versus non-living knowledge were found in both networks using both training sets. We discuss the idea that statistical distributions of impairments in patients with similar lesions are necessary to compare against the predictions of functional models, and thus that single case studies may be insufficient to distinguish distributed and modular architectures.
Access this chapter
Tax calculation will be finalised at checkout
Purchases are for personal use only
Preview
Unable to display preview. Download preview PDF.
References
Small SL, Hart J, Nguyen T, and Gordon B. Distributed representations of semantic knowledge in the brain: Computational experiments using feature based codes. In Reggia J, Ruppin E, and Berndt RS, Neural modelling of brain and cognitive disorders. World Scientific, 1996.
Farah MJ and McClelland JL. A computational model of semantic memory impairment: Modality specificity and emergent category specificity. Journal of Experimental Psychology 1991, Vol. 120(4), 339–357.
Warrington EK. Concrete word dyslexia. British Journal of Psychology 1981, 72, 175–196.
Hart J Jr, Bemdt RS, and Caramazza A. Category-specific naming deficit following cerebral infarction. Nature 1985, 316,439–440.
Sartori G and Job R. The oyster with four legs: A neuropsychological study on the interaction of visual and semantic information. Cognitive Neuropsychology 1988, 5(1), 105–132.
Warrington EK and Shallice T. Category specific semantic impairments. Brain 1984, 106, 859–878.
Warrington EK and McCarthy R. Categories of knowledge: Further fractionation and an attempted integration. Brain 1987,110,1273–1296.
Warrington EK and McCarthy R. Category specific access dysphasia. Brain 1983, 106, 859–878.
Hart J Jr and Gordon B. Neural subsystems for object knowledge. Nature 1992, 359, 60–64.
Silveri MC and Gainotti G. Interaction between vision and language in category-specific semantic impairment. Cognitive Neuropsychology 1988, 5, 677–709.
Basso A, Capitani E, and Laiacona M. Progressive language impairment without dementia: A case with isolated category specific semantic defect. Journal of Neurology, Neurosurgery and Psychiatry 1988, 51, 1201–1207.
Farah MJ, Hammond KH, Mehta Z, and Ratcliff G. Category-specificity and modality-specificity in semantic memory. Neuropsychologia 1989, 8, 1–19.
Hinton GE and Shallice T. Lesioning an attractor network: Investigations of acquired dyslexia. Psychological Review 1991, 98(1), 74–95.
Juola P and Plunkett K. Why double dissociations don’t mean much. In Gernsbacher MA and Derby SJ (Eds.), Proceedings of the 20th Annual Conference of the Cognitive Science Society. Lawrence Erlbaum Associates, 1998, 561–566.
Bullinaria JA and Chater N. Connectionist modelling: Implications for cognitive neuropsychology. Language and Cognitive Processes 1995,10(3/4), 227–264.
Hinton GE. Connectionist learning procedures. Artificial Intelligence 1989, 40, 185–234.
Wood CC. Variations on a theme of Lashley: Lesion experiments on the neural model of Anderson, Silverstein, Ritz & Jones. Psychological Review 1978, 85, 582–591.
Sartori G. From neuropsychological data to theory and vice versa. In Denes G, Bisiacchi P, Semenza C and Andrewsky E (Eds.), Perspectives in cognitive neuropsychology. Hillsdale NJ: Erlbaum, 1988.
Shallice T. From neuropsychology to mental structure. Cambridge: Cambridge University Press, 1988.
Plaut DC. Double dissociation without modularity: Evidence from connectionist neuropsychology. Journal of Clinical and Experimental Neuropsychology 1995, 17(2), 291–321.
Baddeley RJ, Abbott LF, Booth MJA, Sengpiel F, Freeman T, Wakeman EA and Rolls ET. Responses of neurons in primary and inferior visual cortices to natural scenes. Proceedings of the Royal Society 1998, B, in press.
Rolls ET and Treves A. Neural networks and brain function. Oxford University Press, 1998.
Gonnerman LM, Andersen ES, Devlin JT, Kempier D, and Seidenberg MS. Double dissociation of semantic categories in Alzheimer’s disease. Brain and Language 1997, 57, 254–279.
French RM and Mareschal, D. Could category-specific semantic deficits reflect differences in the distributions of features within a unified semantic memory? In Proceedings of the 20th Annual Conference of the Cognitive Science Society, 1998, NJ:LEA, 374–379.
Author information
Authors and Affiliations
Editor information
Editors and Affiliations
Rights and permissions
Copyright information
© 1999 Springer-Verlag London Limited
About this paper
Cite this paper
Thomas, M.S.C., de Wet, N.M. (1999). Stochastic double dissociations in distributed models of semantic memory. In: Heinke, D., Humphreys, G.W., Olson, A. (eds) Connectionist Models in Cognitive Neuroscience. Perspectives in Neural Computing. Springer, London. https://doi.org/10.1007/978-1-4471-0813-9_15
Download citation
DOI: https://doi.org/10.1007/978-1-4471-0813-9_15
Publisher Name: Springer, London
Print ISBN: 978-1-85233-052-1
Online ISBN: 978-1-4471-0813-9
eBook Packages: Springer Book Archive