Natalia Shevtsova
A.B.Kogan Research Institute for Neurocybernetics
Rostov State University, Rostov-on-Don, Russia
e-mail: nisms@krinc.ru

James A. Reggia
Depts. of Computer Science and Neurology, Inst. Adv. Comp. Studies
University of Maryland, USA
e-mail: reggia@cs.umd.edu


The effects of simulated lesions to a bihemispheric letter-identification model are examined in the acute and chronic phases under various assumptions about hemispheric asymmetries, callosal influence, and lesion size and side. In the acute phase, generally a ``mass effect'' is seen: post-lesion performance of the full model worsens as lesion size increases. Up to a lesion size of 80%, both hemispheres usually participate in recovery with more active participation of the damaged hemisphere, and in most cases, full recovery is achieved. For lesions of more than 80%, recovery is partial and due to improvement in the non-damaged hemisphere. Most importantly, the model demonstrates participation of the intact hemisphere in the recovery process as a function of pre-existing lateralization and lesion size, indicating that interpretation of experimental work should take these factors into account.

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