Effects of expansion on consonant recognition and consonant audibility

Background: Hearing aid expansion is intended to reduce the gain for low-level noise. However, expansion can also degrade low-intensity speech. Although it has been suggested that the poorer performance with expansion is due to reduced audibility, this has not been measured directly. Furthermore, previous studies used relatively high expansion kneepoints. Purpose: This study compared the effect of a 30 dB SPL and 50 dB SPL expansion kneepoint on consonant audibility and recognition. Research Design: Eight consonant-vowel syllables were presented at 50, 60, and 71 dB SPL. Recordings near the tympanic membrane were made of each speech token and used to calculate the Aided Audibility Index (AAI). Study Sample: Thirteen subjects with mild to moderate sensorineural hearing loss. Results: Expansion with a high kneepoint resulted in reduced consonant recognition. The AAI correlated significantly with consonant recognition across all conditions and subjects. Conclusion: If consonant recognition is the priority, audibility calculations could be used to determine an optimal expansion kneepoint for a given individual.