A Neuropsychological and Computational Investigation of Past Tense Verb Processing

Carnegie Mellon University, Pittsburgh PA

Investigators

Abstract

The simple process of transforming the present tense of an English verb into its past-tense form has dominated the debate between two fundamentally different views of language knowledge and processing. According to traditional, symbolic theories, language knowledge takes the form of explicit rules operating over discrete, symbolic representations. By contrast, according to connectionist or neural-network theories, language processing involves the massively parallel interaction of large numbers of neuron-like processing units. The principal objective of the proposed work is to implement a connectionist-style computational model that demonstrates the differential influence of semantic and phonological factors on past-tense production and in turn, derives novel predictions that could be assessed by future neuropsychological testing. The computational simulations will extend preliminary work by Joanisse and Seidenberg in which verb processing involved the parallel interaction of representations of phonology (both in comprehension and production) and their meanings. The proposed simulations will incorporate more realistic representations and temporal dynamics. An initial stage of modeling will employ fixed-length phonological representations of monosyllabic verb stems, but a second stage will employ continuous-time trajectories for phonological input and output capable of handling multisyllabic items. Semantic representations will be derived from a number of analyses of large text corpora, including Lund and Burgess' Hyperspace Analogue to Language (HAL), which will be replicated if necessary in order to make the resulting semantic representations publicly available for unrestricted use by other researchers. The development of a strongly theoretically motivated connectionist computational model of selective impairments in English past-tense formation will not only provide important insights into the role of semantic and phonological representations in lexical processing, but also more generally about the fundamental character of the principal components, and their interactions, in the language system.