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Are imaging and lesioning convergent methods for assessing functional specialisation: investigations using an artificial neural network

Thomas, Michael S.C. and Purser, Harry and Tomlinson, S. and Mareschal, Denis (2012) Are imaging and lesioning convergent methods for assessing functional specialisation: investigations using an artificial neural network. Brain and Cognition 78 (1), pp. 38-49. ISSN 0278-2626.

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Official URL: http://dx.doi.org/10.1016/j.bandc.2011.10.003

Abstract

This article presents an investigation of the relationship between lesioning and neuroimaging methods of assessing functional specialisation, using synthetic brain imaging (SBI) and lesioning of a connectionist network of past-tense formation. The model comprised two processing ‘routes’: one was a direct route between layers of input and output units, while the other, indirect, route featured an intermediate layer of processing units. Emergent specialisation within the network was assessed (1) by lesioning either the direct or indirect route and measuring past-tense performance for regular and irregular verbs, and (2) by measuring functional activation in each route when processing each verb type (SBI). SBI and lesioning approaches failed to converge when network activation was summed over each route in our SBI approach. Examination of individual network solutions suggested that the verb types might be using the indirect route differently in terms of the pattern of activation across the route, rather than in terms of gross activation. A subsequent SBI analysis compared patterns of activation in the indirect route and confirmed that these patterns were more similar between regular-type verbs than between regular and irregular verbs. As the spatial and temporal resolution of neuroimaging techniques improves, the results of this investigation suggest that the key to finding functional specialisation will be to distinguish local coding differences across behaviours that are the results of developmental processes. Other analyses suggest that lesioning data may be limited because, with increasing damage, they reveal the resting activations of a computational system rather than a computational specialisation per se.

Item Type: Article
Keyword(s) / Subject(s): Neuropsychology, Neuroimaging, Synthetic brain imaging, Computational modelling, Connectionism, Neural network, Language, Past tense, Functional specialisation
School or Research Centre: Birkbeck Schools and Research Centres > School of Science > Psychological Sciences
Depositing User: Administrator
Date Deposited: 16 Nov 2011 09:21
Last Modified: 17 Apr 2013 12:21
URI: http://eprints.bbk.ac.uk/id/eprint/4372

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