The effect of phonological neighborhood density and word frequency on vowel production and perception in clear speech

Abstract

Previous research showed that phonological neighborhood density and word frequency influence word recognition (Luce and Pisoni, 1998) and vowel production (Wright, 2002; Munson and Solomon, 2004; Munson, to appear), suggesting an interaction of lexical and phonetic factors in speech production and perception Here, we explore whether hyperarticulated, intelligibility-enhancing clear speech shows similar sensitivity to lexical-level structure. Nine American English talkers (five females, four males) produced 40 monosyllabic easy (frequent words with few lexical neighbors) and hard (infrequent words with many lexical neighbors) words in conversational and clear speech. Twenty-four subjects participated in a word-in-noise listening test. Results revealed a large effect of style on intelligibility and vowel production: words were more intelligible and vowels were longer and more dispersed in clear compared to conversational speech. Moreover, the female talkers produced larger vowel spaces than male talkers in both speaking styles. Vowels in hard words were marginally more dispersed than vowels in easy words in both speaking styles. However, within both speaking styles, easy and hard words were equally intelligible and of approximately equal duration. These results showed that phonetic properties of vowels were enhanced equally in clear speech regardless of their lexical properties.