International Journal of Speech Technology

, Volume 3, Issue 1, pp 15–25 | Cite as

The Effect of Lexical Complexity on Intelligibility

  • Alexander L. Francis
  • Howard C. Nusbaum


Most intelligibility tests are based on the use of monosyllabictest stimuli. This constraint eliminates the ability to measurethe effects of lexical stress patterns, complex phonotacticorganizations, and morphological complexity on intelligibility.Since these aspects of lexical structure affect speechproduction (e.g., by changing syllable duration), it is likelythat they affect the structure of acoustic-phonetic patterns.Thus, to the extent that text-to-speech systems fail to modifyacoustic-phonetic patterns appropriately in polysyllabic words,intelligibility may suffer. This means that while most standardintelligibility tests may accurately estimate theintelligibility of monosyllabic words, this estimate may notgeneralize as well to predict the intelligibility of words withmore complex lexical structures. The present study was carriedout to measure how words varying in lexical complexity differ inintelligibility. Monosyllabic, bisyllabic, and polysyllabicwords were used varying in morphological complexity(monomorphemic or polymorphemic). Listeners transcribed thesestimuli spoken by two human talkers and two text-to-speechsystems varying in speech quality. The results indicate thatlexical complexity does affect the measured intelligibility ofsynthetic speech and should be manipulated in order toaccurately predict the performance of text-to-speech systemswith unrestricted natural text.

text-to-speech intelligibility assessment lexical complexity 


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Copyright information

© Kluwer Academic Publishers 1999

Authors and Affiliations

  • Alexander L. Francis
    • 1
  • Howard C. Nusbaum
    • 1
  1. 1.Department of PsychologyUniversity of ChicagoChicago

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