Impairments in verb morphology after brain injury: A connectionist model

The formation of the past tense of verbs in English has been the focus of t he debate concerning connectionist vs. symbolic accounts of language. Brain -injured patients differ with respect to whether they are more impaired in generating irregular past tenses (TAKE-TOOK) or past tenses for nonce verbs (WUG-WUGGED). Such dissociations ha, have been taken as evidence for disti nct "rule" and "associative" memory systems in morphology and against the c onnectionist approach in which a single system is used for all forms. We de scribe a simulation model in which these impairments arise from damage to p honological or semantic information, which have different effects on genera lization and irregular forms, respectively. The results pro,ide an account of the bases of impairments in verb morphology and show that these impairme nts can be explained within connectionist models that do not use rules or a separate mechanism for exceptions.