A case-series test of the interactive two-step model of lexical access: evidence from picture naming. Journal of memeory and language

Computational models of aphasia must, first, characterize the actions of the unimpaired system, and then explain how that system is damaged in aphasia. Our model of lexical deficits in aphasic speakers is based on the interactive two-step theory, an account of normal lexical access in production that associates the process with two distinct steps, word retrieval and phonological retrieval. Each step is achieved by the interactive, or bidirectional, spread of activation through a layered network of units for semantic features, words, and phonemes (Fig. 1). Deficits are created by altering parameters that affect activation. In our first model of this type, the weight-decay model (Dell, Schwartz, Martin, Saffran, & Gagnon, 1997), lesions corresponded to global decreases in the weight of connections among all units in the network (parameter w) and global increases in the rate with which activation decays (parameter d). The more recent se-mantic-phonological model (Foygel & Dell, 2000) also had two le