Lexical similarity and speech production: Neighborhoods for nonwords

Abstract Lexical similarity has been shown to play a role in speech production (as in speech perception). In production, words with many phonologically similar neighbors, i.e., those that are phonologically similar to a large number of other words, are produced with more hyperarticulated vowels than words with fewer neighbors ( Wright, 1997 , Munson and Solomon, 2004 ). The experiments presented here further investigate the role that lexical similarity, expressed in terms of phonological neighborhood density, plays in the details of phonetic implementation, looking at nasal coarticulation in particular. And the way in which the grammar might produce such effects is probed by looking for neighborhood-conditioned effects in not only real words, but also nonsense words. Eight speakers of American English produced 48 highly familiar CVN or NVC words and 48 similar CVN or NVC word-like nonsense words with either many or few phonologically similar neighbors (words differing from the target word by a single phoneme). Lexical frequency and segmental context were balanced across neighborhood conditions. Degree of nasal coarticulation was measured acoustically on each vowel (A1-P0) ( Chen, 1997 ), along with vowel duration and spectral hyperarticulation. Analysis showed that real words (both CVNs and NVCs) from dense neighborhoods (e.g., band, mug) were consistently and reliably produced with more coarticulation and more hyperarticulation than words from sparse neighborhoods (e.g., stem, mouth). Vowel duration was not affected. The same consistent effects of neighborhood were found for nonsense words as well (e.g., gand, mub vs. blem, maub) for approximately half of the speakers in the study. The other speakers showed consistently opposite effects for nonsense words (i.e., greater nasal coarticulation and hyperarticulation in nonsense words from sparse neighborhoods), despite patterning with the rest of the speakers for real words. These findings demonstrate that phonological similarity at the lexical level has an influence on phonetic realization: similarity to a greater number of real words is associated with increased coarticulation as well as hyperarticulation. Interestingly, the degree of coarticulation and hyperarticulation vary systematically in nonwords as well, but the nature of the systematic relationship differs across two groups of speakers: some speakers produce nonsense words just like real words with increased hyperarticulation and coarticulation in nonsense words from dense neighborhoods, while other speakers produce nonsense words with the opposite systematic relationship—with increased hyperarticulation and coarticulation in nonsense words from sparse neighborhoods. However, because nonsense words, like real words, show some kind of systematic relationship between detail in production and lexical similarity neighborhoods, the differences in phonetic implementation must not be encoded directly in the representation, as nonwords have no long-term representations. Rather, lexical similarity must be assessed online with active reference to a space in the lexicon (the neighborhood).