Clear speech is a form of communication that talkers naturally use when speaking in difficult listening conditions or with a person who has a hearing loss. Clear speech, on average, provides listeners with hearing impairments an intelligibility benefit of 17 percentage points (Picheny, Durlach, & Braida, 1985) over conversational speech. In addition, it provides increased intelligibility in various listening conditions (Krause & Braida, 2003, among others), with different stimuli (Bradlow & Bent, 2002; Gagne, Rochette, & Charest, 2002; Helfer, 1997, among others) and across listener populations (Bradlow, Kraus, & Hayes, 2003, among others). Recently, researchers have attempted to compare their findings with clear and conversational speech, at slow and normal rates, with results from other investigators' studies in an effort to determine the relative benefits of clear speech across populations and environments. However, relative intelligibility benefits are difficult to determine unless baseline performance levels can be equated, suggesting that listener psychometric functions with clear speech are needed. The purpose of this study was to determine how speech intelligibility, as measured by percentage key words correct in nonsense sentences by young adults, varies with changes in speaking condition, talker and signal-to-noise ratio (SNR). Forty young, normal hearing adults were presented with grammatically correct nonsense sentences at five SNRs. Each listener heard a total of 800 sentences in four speaking conditions: clear and conversational styles, at slow and normal rates (i.e., clear/slow, clear/normal, conversational/slow, and conversational/normal). Overall results indicate clear/slow and conversational/slow were the most intelligible conditions, followed by clear/normal and then conversational/normal conditions. Moreover, the average intelligibility benefit for clear/slow, clear/normal and conversational/slow conditions (relative to conversational/normal) was maintained across an SNR range of -4 to 0 dB in the middle, or linear, portion of the psychometric function. However, when results are examined by talker, differences are observed in the benefit provided by each condition and in how the benefit varies across noise levels. In order to counteract talker variability, research with a larger number of talkers is recommended for future studies.

Clear speech refers to a speaking style that is more intelligible than typical, conversational speaking styles. It is usually produced at a slower rate compared to conversational speech. Clear speech has been shown to be more intelligible than conversational speech for a large variety of populations, including both hearing impaired (Schum, 1996; Picheny, Durlach, & Braida, 1985; and Payton, Uchanski, & Braida, 1994) and normal hearing individuals (e.g. Uchanski, Choi, Braida, Reed, & Durlach, 1996) under a variety of conditions, including those in which presentation level, speaker, and environment are varied. Although clear speech is typically slower than normally produced conversational speech, recent studies have shown that it can be produced at normal rates with training (Krause & Braida, 2002). If clear speech at normal rates is shown to be as effective for individuals with hearing loss as clear speech at slow rates, it would have both clinical and research implications. The purpose of this study was to determine the effectiveness of clear speech at normal rates for older individuals with hearing loss. It examined the way in which intelligibility, measured as percent correct keyword scores on nonsense sentences, varied as a result of speaking mode (clear versus conversational speech) and speaking rate (slow versus normal) in six adults aged 55-75 years old with moderate, sloping, hearing loss. Each listener was presented with nonsense sentences in four speech conditions: clear speech at slow rates (clear/slow), clear speech at normal rates (clear/normal), conversational speech at slow rates (conv/slow), and conversational speech at normal rates (conv/normal) read by four different talkers. Sentences were presented monaurally in quiet to the listeners via headphones. Results indicated that clear/slow speech was the most intelligible condition overall. Neither conv/slow nor clear/normal provided an intelligibility benefit relative to conv/normal speech on average, suggesting that for older adults with moderate, sloping hearing loss, the combination of using clear speech and a slower speaking rate is more beneficial to intelligibility than the additive effects of altering either speaking rate or speaking mode alone. It has been suggested previously (Krause, 2001) that audiological characteristics may contribute to the lack of clear/normal benefit for certain listeners with hearing loss. Although clear/normal speech was not beneficial on average to listeners in this study, there were cases in which the clear/normal speech of a particular talker provided a benefit to a particular listener. Thus, severity and configuration of hearing loss alone cannot fully explain the degree to which listeners from hearing loss do (or do not) benefit from clear/normal speech. More studies are needed to investigate the benefits of clear/normal speech for different audiological configurations, including individuals with flat losses. In addition, the listening tasks should include more difficult conditions in order to compensate for potential ceiling effects.