Graduation Year


Document Type




Degree Granting Department

Speech-language Pathology

Major Professor

Jean C. Krause, Ph.D.

Committee Member

Theresa Hnath-Chisolm, Ph.D.

Committee Member

Jennifer Lister, Ph.D.


Speech intelligibility, Speaking rate, Hearing impaired, Aging, Acoustic properties, Hearing aids, Communication breakdown


Clear speech is a type of speaking style that improves speech intelligibility for many individuals. For example, one study showed a 17 percentage point increase in intelligibility over conversational speech for individuals with sensorineural hearing loss (Picheny et al., 1985). The clear speech benefit also extends to children with learning disabilities (Bradlow et al., 2003), non-native listeners (Bradlow & Bent, 2002), and other populations. Although clear speech is typically slower than conversational speech, it can be produced, naturally, at normal rates with training. For young listeners with normal hearing, clear speech at normal rates (clear/normal) is more intelligible than conversational speech (conv/normal) and is almost as beneficial as clear speech at slow rates (clear/slow) (Krause & Braida, 2002). However, a preliminary study by Krause (2001), found that clear/normal speech may benefit some older listeners with hearing loss but not others, suggesting that age may be a factor in the clear speech benefit at normal rates. It is evident, though, that clear speech at slow rates benefits this population (Picheny et al., 1985; Payton et al., 1994; Schum, 1996; Helfer, 1998). Therefore, the purpose of the study was to examine older listeners with normal hearing to determine how speech intelligibility, measured by % correct keyword scores, varies with speaking mode, speaking rate, talker and listener. Results were then compared to previously collected data from younger listeners with normal hearing (Krause & Braida, 2002) in order to isolate the effect of age on the size of clear speech benefit at slow and normal speaking rates.

Eight adults (ages 55-68) with normal hearing participated in speech intelligibility tests. Each listener was presented with the speech of 4 talkers in 4 speaking styles: conv/normal, clear/normal, conv/slow and clear/slow, drawn from recordings made for an earlier study (Krause & Braida, 2002). Stimuli were nonsense sentences presented monoaurally with speech-shaped noise in the background.

Results showed that clear/slow and conv/slow were the most intelligible speaking conditions. However, clear/normal was also more intelligible than conv/normal, demonstrating that a talker does not need to decrease rate to improve intelligibility for listeners with normal hearing, regardless of age.

More studies are needed to investigate any similarities between conv/slow and clear/slow, since performance by older listeners was highest in these two conditions. Signal-to-noise ratio (SNR) also needs to be controlled in future studies to further characterize the effect of age on clear speech benefits at slow and normal speaking rates.