Amplification and consonant modulation spectra.

OBJECTIVE: In previous work, a simplified version of the modulation spectrum, the Spectral Correlation Index, was shown to be related to consonant error patterns. It is unknown what effect clinical amplification strategies will have on the modulation spectrum. Accordingly, the goals of this study were to examine the effect of clinical amplification strategies on the consonant modulation spectrum and to determine whether there was a relationship between the modulation spectrum and consonant errors for spectrally robust, amplified speech presented to listeners with hearing loss.
DESIGN: Participants were 13 adults (mean age, 67 yrs) with mild to moderate sensorineural hearing loss. Each listener was fit monaurally in the test ear with a 16-band, four-channel behind the ear hearing aid. One memory of the hearing aid was programmed with compression limiting amplification and one with fast-acting wide-dynamic range compression (WDRC) amplification. Twenty-two consonant-vowel syllables were presented to the listener and recorded at the output of the hearing aid using a probe microphone system. A modulation spectrum was obtained for each amplified and unamplified consonant-vowel. Consonant recognition was also measured for each listener.
RESULTS: Results show that (1) WDRC increased heterogeneity of the modulation spectrum across consonants and (2) for spectrally robust speech processed with either compression limiting or WDRC amplification, two consonants with similar modulation spectra are more likely to be confused with one another than are the two consonants with dissimilar modulation spectra.
CONCLUSION: These data expand and confirm earlier results linking the modulation spectrum to specific consonant errors.