ORIGINS OF PARAPHASIAS IN DEEP DYSPHASIA - TESTING THE CONSEQUENCES OF A DECAY IMPAIRMENT TO AN INTERACTIVE SPREADING ACTIVATION MODEL OF LEXICAL RETRIEVAL

This study investigates an account of atypical error patterns within t he framework of an interactive spreading activation model. Martin and Saffran (1992) described a patient, NC, whose error pattern was unusua l for the occurrence of higher rates of form-related than meaning-rela ted word substitutions in naming and the production of semantic errors in repetition. They proposed that NC's error pattern could be account ed for by a pathologically rapid decay of primed nodes in the semantic -lexical-phonological network that shifts the probabilities of error o utcome in lexical retrieval. In the present study, Martin and Saffran' s account was tested and supported in a series of simulations that rep roduce essential features of NC's lexical error pattern in naming and repetition. Also described here are the results of a longitudinal stud y of NC's naming and repetition, which revealed a shift in relative le xical error rates toward a qualitatively normal pattern. This change i n error pattern was simulated by assuming that recovery reflects resol ution of the rapid decay rate toward normal levels. The patient data a nd computational studies are discussed in terms of their significance for the understanding of aphasic impairments and their implications fo r models of lexical retrieval. (C) 1994 Academic Press, Inc.