Being clear about clear speech: Intelligibility of hard-of-hearing-directed, non-native-directed, and casual speech for L1- and L2-English listeners

Relative to one's default (casual) speech, clear speech contains acoustic modifications that are often perceptually beneficial. Clear speech encompasses many different styles, yet most work only compares clear and casual speech as a binary. Furthermore, the term "clear speech" is often unclear − despite variation in elicitation instructions across studies (e.g., speak clearly, imagine an L2-listener or someone with hearing loss, etc.), the generic term "clear speech" is used when interpreting results, under the tacit assumption that clear speech is monolithic. The current study examined the acoustics and intelligibility of casual speech and two clear styles (hard-of-hearing-directed and non-native-directed speech). We find: (1) the clear styles are acoustically distinct (non-native-directed speech is slower with lower mean intensity and f0); (2) the clear styles are perceptually distinct (only hard-of-hearing-directed speech enhances intelligibility); (3) no differences in intelligibility benefits are observed between L1 and L2-listeners. These results underscore the importance of considering the intended interlocutor in speaking style elicitation, leading to a discussion about the issues that arise when reference to "clear speech" lacks clarity. It is suggested that to be more clear about clear speech, greater caution should be taken when interpreting results about speaking style variation.