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Stephen R. Welbourne
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Journal Articles
Anna C. Schapiro, James L. McClelland, Stephen R. Welbourne, Timothy T. Rogers, Matthew A. Lambon Ralph
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2013) 25 (12): 2107–2123.
Published: 01 December 2013
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Human and animal lesion studies have shown that behavior can be catastrophically impaired after bilateral lesions but that unilateral damage often produces little or no effect, even controlling for lesion extent. This pattern is found across many different sensory, motor, and memory domains. Despite these findings, there has been no systematic, computational explanation. We found that the same striking difference between unilateral and bilateral damage emerged in a distributed, recurrent attractor neural network. The difference persists in simple feedforward networks, where it can be understood in explicit quantitative terms. In essence, damage both distorts and reduces the magnitude of relevant activity in each hemisphere. Unilateral damage reduces the relative magnitude of the contribution to performance of the damaged side, allowing the intact side to dominate performance. In contrast, balanced bilateral damage distorts representations on both sides, which contribute equally, resulting in degraded performance. The model's ability to account for relevant patient data suggests that mechanisms similar to those in the model may operate in the brain.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2007) 19 (7): 1125–1139.
Published: 01 July 2007
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PMSP96 [Plaut, D. C., McClelland, J. L., Seidenberg, M. S., & Patterson, K. Understanding normal and impaired word reading: Computational principles in quasi-regular domains. Psychological Review, 103 , 56–115, 1996, Simulation 4] is an implementation of the triangle model of reading, which was able to simulate effects found in normal and surface dyslexic readers. This study replicated the original findings and explored the possibility that damage to the phonological portion of the model might produce symptoms of phonological dyslexia. The first simulation demonstrated that this implementation of PMSP96 was able to reproduce the standard effects of reading, and that when damaged by removal of the semantic input to phonology, it produced the kind of frequency/consistency interactions and regularization errors typical of surface dyslexia. The second simulation explored the effect of phonological damage. Phonological damage alone did not result in a convincing simulation of phonological dyslexia. However, when the damage was followed by a period of recovery, the network was able to simulate large lexicality and imageability effects characteristic of phonological dyslexia-the first time that both surface and phonological dyslexia have been simulated in the same parallel distributed processing network. This result supports the view that plasticity-related changes should be a significant factor in our understanding of chronic behavioral dissociations.