Pii: S0010-0277(00)00063-9

We present the design, implementation and simulation results of a psycholinguistic model of human syntactic processing that meets major empirical criteria. The parser operates in conjunction with a lexicalist grammar and is driven by syntactic information associated with heads of phrases. The dynamics of the model are based on competition by lateral inhibition (`competitive inhibition'). Input words activate lexical frames (i.e. elementary trees anchored to input words) in the mental lexicon, and a network of candidate `uni®cation links' is set up between frame nodes. These links represent tentative attachments that are graded rather than all-or-none. Candidate links that, due to grammatical or `treehood' constraints, are incompatible, compete for inclusion in the ®nal syntactic tree by sending each other inhibitory signals that reduce the competitor's attachment strength. The outcome of these local and simultaneous competitions is controlled by dynamic parameters, in particular by the Entry Activation and the Activation Decay rate of syntactic nodes, and by the Strength and Strength Build-up rate of Uni®cation links. In case of a successful parse, a single syntactic tree is returned that covers the whole input string and consists of lexical frames connected by winning Uni®cation links. Simulations are reported of a signi®cant range of psycholinguistic parsing phenomena in both normal and aphasic speakers of English: (i) various effects of linguistic complexity (single versus double, center versus right-hand self-embeddings of relative clauses; the difference between relative clauses with subject and object extraction; the contrast between a complement clause embedded within a relative clause versus a relative clause embedded within a complement clause); (ii) effects of local and global ambiguity, and of word-class and syntactic ambiguity (including recency and length effects); (iii) certain dif®culty-ofreanalysis effects (contrasts between local ambiguities that are easy to resolve versus ones that lead to serious garden-path effects); (iv) effects of agrammatism on parsing performance, Cognition 75 (2000) 105±143 COGN I T I O N 0010-0277/00/$ see front matter q 2000 Elsevier Science B.V. All rights reserved. PII: S0010-0277(00)00063-9 www.elsevier.com/locate/cognit * Corresponding author. E-mail addresses: [email protected] (T. Vosse); [email protected] (G. Kempen) in particular the performance of various groups of aphasic patients on several sentence types. q 2000 Elsevier Science B.V. All rights reserved.