Several studies have demonstrated that when talkers are instructed to speak clearly, the resulting speech is significantly more intelligible than speech produced in ordinary conversation. These speech intelligibility improvements are accompanied by a wide variety of acoustic changes. The current study explored the relationship between acoustic properties of vowels and their identification in clear and conversational speech, for young normal-hearing (YNH) and elderly hearing-impaired (EHI) listeners. Monosyllabic words excised from sentences spoken either clearly or conversationally by a male talker were presented in 12-talker babble for vowel identification. While vowel intelligibility was significantly higher in clear speech than in conversational speech for the YNH listeners, no clear speech advantage was found for the EHI group. Regression analyses were used to assess the relative importance of spectral target, dynamic formant movement, and duration information for perception of individual vowels. For both listener groups, all three types of information emerged as primary cues to vowel identity. However, the relative importance of the three cues for individual vowels differed greatly for the YNH and EHI listeners. This suggests that hearing loss alters the way acoustic cues are used for identifying vowels.

These results suggest that acoustic vowel space expansion and large vowel duration increases improve vowel intelligibility. In contrast, changing the dynamic characteristics of vowels seems not to contribute to improved clear speech vowel intelligibility. However, talker variability suggested that improved vowel intelligibility can be achieved using a variety of clear speech strategies, including some apparently not measured here.

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Several studies have shown that when a talker is instructed to speak as though talking to a hearing-impaired person, the resulting "clear" speech is significantly more intelligible than typical conversational speech. While variability among talkers during speech production is well known, only one study to date [Gagné et al., J. Acad. Rehab. Audiol. 27, 135-158 (1994)] has directly examined differences among talkers producing clear and conversational speech. Data from that study, which utilized ten talkers, suggested that talkers vary in the extent to which they improve their intelligibility by speaking clearly. Similar variability can be also seen in studies using smaller groups of talkers [e.g., Picheny, Durlach, and Braida, J. Speech Hear. Res. 28, 96-103 (1985)]. In the current paper, clear and conversational speech materials were recorded from 41 male and female talkers aged 18 to 45 years. A listening experiment demonstrated that for normal-hearing listeners in noise, vowel intelligibility varied widely among the 41 talkers for both speaking styles, as did the magnitude of the speaking style effect. While female talkers showed a larger clear speech vowel intelligibility benefit than male talkers, neither talker age nor prior experience communicating with hearing-impaired listeners significantly affected the speaking style effect.

Purpose To establish the range of talker variability for vowel intelligibility in clear versus conversational speech for older adults with hearing loss and to determine whether talkers who produced a clear speech benefit for young normal-hearing listeners also do so for older adults with hearing loss. Method Clear and conversational vowels in /bVd/ context produced by 41 talkers were presented in noise for identification by 40 older adults with sloping sensorineural hearing loss. Results Vowel intelligibility within each speaking style and the size of the clear speech benefit varied widely among talkers. The clear speech benefit was equivalent to that enjoyed by young normal-hearing listeners in an earlier study. Most talkers who had produced a clear speech benefit for young listeners with normal hearing also did so for the current older listeners with hearing loss. However, effects of talker gender differed between listeners with normal hearing and listeners with hearing loss. Conclusion The clear speech vowel intelligibility benefit generated for listeners with hearing loss varies considerably among talkers. Most talkers who produce a clear speech benefit for normal-hearing listeners also produce a benefit for listeners with hearing loss.