Clinical Applications for Time-Compressed Speech Tests

Recent research has shown the relevance of cognitive function in hearing aid evaluation and the sensitivity of the aging auditory system to temporal distortions. The proposed investigation will examine the interaction of working memory and hearing aid compression method on speech recognition in background competition for older listeners. This interaction will be investigated for the following three forms of background competition:

• Competition from continuous speech-shaped noise.
• Competition from speech-modulated noise.
• Competition from a single interfering talker.

The goals of the study will be accomplished in two phases. In the first phase, 160 adults aged 50 through 75 years will be evaluated on a battery of tests to determine their cognitive capacity, time-compressed speech scores and their candidacy for inclusion in the second phase of the study. At the conclusion of this phase of testing, the participants will be divided into three groups:

• subjects with TCS test scores in the highest quartile (the HIGH group)
• subjects with TCS test scores in the lowest quartile (the LOW group)
• the remaining listeners

The second phase of the experiment will include listeners from the HIGH and LOW groups only. These subjects will be evaluated with respect to their speech recognition ability for three types of interference (steady-state noise, speech-modulated noise, single interfering talker). The HINT test (Nilsson, Soli, & Sumida, 1995; Nilsson et al., 1994) will be used to obtain the signal-to-noise ratio (SNR) at 50% recognition for the three masking conditions for each of three types of amplification:

• one- channel linear amplification (LINEAR) with frequency shaping
• two-channel wide dynamic range compression with fast time constants (FAST)
• two-channel wide dynamic range compression with slow time constants (SLOW) Listener groups will be compared across hearing aid conditions and across background interference conditions.

Inclusion criteria

• Participants will be 50 to 75 years old.
• Hearing loss will be limited to 40 dB HL from 250 Hz through 1000 Hz, and to 60 dB HL through 4000 Hz.
• Hearing loss must be greater than 25 dB at two or more frequencies from 250 to 4000 Hz.

Exclusion criteria

• None of the participants will be current or past hearing aid users; all will be free of ear disease.
• Participants with conductive hearing losses, defined as air-bone gap greater than 15 dB, will be excluded.
• The audiometric battery with acoustic reflex thresholds and decay measurements will be used to exclude anyone with evidence of a central disorder or a pathology other than a sensorineural loss. Those potential participants will be referred to a medical professional.