Methods for Minimizing the Confounding Effects of Word Length in the Analysis of Phonotactic Probability and Neighborhood Density Recent research suggests that phonotactic probability (the likelihood of occurrence of a sound sequence) and neighborhood density (the number of words phonologically similar to a given word) influence spoken language processing and acquisition across the lifespan in both normal and clinical populations. The majority of research in this area has ... Research Note
Research Note  |   December 01, 2004
Methods for Minimizing the Confounding Effects of Word Length in the Analysis of Phonotactic Probability and Neighborhood Density
 
Author Affiliations & Notes
  • Holly L. Storkel
    University of Kansas
  • Corresponding author: e-mail: hstorkel@ku.edu
  • Contact author: Holly Storkel, Department of Speech- Language-Hearing: Sciences and Disorders, University of Kansas, 3001 Dole Human Development Center, 1000 Sunnyside Avenue, Lawrence, KS 66045-7555.
    Contact author: Holly Storkel, Department of Speech- Language-Hearing: Sciences and Disorders, University of Kansas, 3001 Dole Human Development Center, 1000 Sunnyside Avenue, Lawrence, KS 66045-7555.×
Article Information
Speech, Voice & Prosodic Disorders / Cultural & Linguistic Diversity / Normal Language Processing / Speech, Voice & Prosody / Language / Research Notes
Research Note   |   December 01, 2004
Methods for Minimizing the Confounding Effects of Word Length in the Analysis of Phonotactic Probability and Neighborhood Density
Journal of Speech, Language, and Hearing Research, December 2004, Vol. 47, 1454-1468. doi:10.1044/1092-4388(2004/108)
History: Received January 7, 2004 , Accepted March 30, 2004
 
Journal of Speech, Language, and Hearing Research, December 2004, Vol. 47, 1454-1468. doi:10.1044/1092-4388(2004/108)
History: Received January 7, 2004; Accepted March 30, 2004
Web of Science® Times Cited: 58

Recent research suggests that phonotactic probability (the likelihood of occurrence of a sound sequence) and neighborhood density (the number of words phonologically similar to a given word) influence spoken language processing and acquisition across the lifespan in both normal and clinical populations. The majority of research in this area has tended to focus on controlled laboratory studies rather than naturalistic data such as spontaneous speech samples or elicited probes. One difficulty in applying current measures of phonotactic probability and neighborhood density to more naturalistic samples is the significant correlation between these variables and word length. This study examines several alternative transformations of phonotactic probability and neighborhood density as a means of reducing or eliminating this correlation with word length. Computational analyses of the words in a large database and reanalysis of archival data supported the use of z scores for the analysis of phonotactic probability as a continuous variable and the use of median transformation scores for the analysis of phonotactic probability as a dichotomous variable. Neighborhood density results were less clear with the conclusion that analysis of neighborhood density as a continuous variable warrants further investigation to differentiate the utility of z scores in comparison to median transformation scores. Furthermore, balanced dichotomous coding of neighborhood density was difficult to achieve, suggesting that analysis of neighborhood density as a dichotomous variable should be approached with caution. Recommendations for future application and analyses are discussed.

Acknowledgments
This work was supported by National Institutes of Health Grants DC04781 and DC06545. Michael Vitevitch aided in the computation of the phonotactic probabilities and neighborhood density and provided comments on an earlier version of this article. We are further indebted to Michael Vitevitch for generously providing the raw data from Vitevitch and Luce (1998)  and Experiment 4 of Vitevitch and Luce (1999) .
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