The effect of clear speech to foreign-sounding interlocutors on native listeners’ perception of intelligibility

Hyperarticulation is an acoustic modification of the speech stream that has been reliably shown to be naturally part of clear speech. Despite the large number of studies that have investigated the relationship between clear speech properties (e.g. expanded vowel space) and intelligibility, only an associative, rather than a causal relationship between vowel space expansion and speech intelligibility has been documented to this date. The focus of this study was to more directly explore the impact of vowel hyperarticulation on intelligibility. Specifically, it tested the effect that naturally elicited speech in interaction with native-sounding adults and foreign-sounding adults had on intelligibility. Twenty-one native speakers of English transcribed and provided ratings of typicality and clarity for speech that was produced while speakers were interacting with native-sounding and foreign-sounding adults. Results revealed that speech directed at L2 speakers is more intelligible and rated as being clearer and a more typical representation of speech compared to speech directed at L1 speakers. Implications of the findings are discussed in terms of Lindblom's Hyper-and Hypoarticulation theory (1992)