Effect of Envelope Enhancement on Speech Perception in Individuals with Auditory Neuropathy

Abstract

To investigate the ability to identify consonant-vowel (CV) stimuli by individuals with auditory neuropathy (AN) when the envelope of the speech signal is enhanced by 15 dB for different modulation bandwidths (3 to 10 Hz; 3 to 20 Hz; 3 to 30 Hz; 3 to 60 Hz). Eight individuals with auditory neuropathy whose pure-tone thresholds ranged from 30 to 70 dB HL participated in the present study. Speech material consisted of five lists of CV, one unprocessed and four with envelope enhancement. The magnitude of envelope enhancement was 15 dB and the bandwidths used were 3 to 10 Hz, 3 to 20 Hz, 3 to 30 Hz, and 3 to 60 Hz. Speech identification scores improved when the envelope of the speech was enhanced. The improvement was greater for the broader bandwidth (3 to 30 Hz) conditions when compared with the smaller bandwidth (3 to 10 Hz and 3 to 20 Hz) conditions. In the unprocessed condition, manner of articulation was transmitted better than voicing and place of articulation. In the envelope-enhanced conditions, cues for manner and place of articulation were transmitted better than voicing. Envelope enhancement using digital techniques improves speech perception by individuals with auditory neuropathy, and it may be a viable option for the rehabilitation of these individuals. However, the magnitude of envelope enhancement of speech required for maximal improvement of speech perception is yet to be determined.