Complexity metrics in an incremental right-corner parser

  • Authors:
  • Stephen Wu;Asaf Bachrach;Carlos Cardenas;William Schuler

  • Affiliations:
  • University of Minnesota;Unit de Neuroimagerie Cognitive INSERM-CEA;Massachussetts Institute of Technology;University of Minnesota and The Ohio State University

  • Venue:
  • ACL '10 Proceedings of the 48th Annual Meeting of the Association for Computational Linguistics
  • Year:
  • 2010

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Abstract

Hierarchical HMM (HHMM) parsers make promising cognitive models: while they use a bounded model of working memory and pursue incremental hypotheses in parallel, they still achieve parsing accuracies competitive with chart-based techniques. This paper aims to validate that a right-corner HHMM parser is also able to produce complexity metrics, which quantify a reader's incremental difficulty in understanding a sentence. Besides defining standard metrics in the HHMM framework, a new metric, embedding difference, is also proposed, which tests the hypothesis that HHMM store elements represents syntactic working memory. Results show that HHMM surprisal outperforms all other evaluated metrics in predicting reading times, and that embedding difference makes a significant, independent contribution.