Hearing-impaired (HI) listeners who benefit from hearing-aid use in quiet often continue to have difficulty understanding speech in noise. Requesting talkers to speak clearly is one strategy to overcome this deficit. Paradoxically, one feature of clear speech is a shift to higher frequencies, which may move speech energy into a frequency range that is inaudible or more distorted for some HI listeners. Casual (or conversational) speech, on the other hand, may shift speech energy into a lower frequency range that is more audible or less distorted. This study examined the intelligibility of 21 amplified, casually- and clearly-spoken, US English coda consonants in nonsense syllables for 10 normal-hearing (NH) and 17 HI listeners. Most clear-speech consonants yielded higher recognition scores as expected. However, certain phonological processes common in casual speech, such as palatalization of higher frequency alveolar into lower frequency postalveolar consonants, generated significantly higher scores than their clear counterparts for some HI listeners in noise. These results have implications for coaching conversational partners of aided HI listeners. For the military, talkers can be instructed how to speak to Service members with hearing loss or in noisy environments.
Keywords: Allophones; casual speech; clear speech; consonants; hearing impairment.