Incremental parsing in a continuous dynamical system: sentence processing in Gradient Symbolic Computation

Abstract

Abstract Any incremental parser must solve two computational problems: (1) maintaining all interpretations consistent with the words that have been processed so far and (2) excluding all globally-incoherent interpretations. While these problems are well understood, it is not clear how the dynamic, continuous mechanisms that underlie human language processing solve them. We introduce a Gradient Symbolic Computation (GSC) parser, a continuous-state, continuous-time stochastic dynamical-system model of symbolic processing, which builds up a discrete symbolic structure gradually by dynamically strengthening a discreteness constraint. Online, interactive tutorials with open-source software are presented in a companion website. Our results reveal that the GSC parser can solve the two computational problems by moving to a non-discrete blend state that evolves exclusively to discrete states representing contextually-appropriate globally-coherent interpretations. In a simulation study using a simple formal grammar, we show that successful parsing requires appropriate control of the discreteness constraint strength (a quantization policy). With inappropriate quantization policies, the GSC parser makes mistakes that mirror those made in natural language comprehension (garden-path or local-coherence errors). These findings suggest that the GSC model offers a neurally plausible solution to these two core problems.