Consonant enhancement effects on speech recognition of hearing-impaired children

This dissertation examined the effects of consonant enhancement on speech recognition by hearing-impaired children. The goal of this research was to determine if there is an optimal consonant amplitude in relation to a neighboring vowel whereby consonant recognition is maximized. The differences in gain required (enhancement, in dB) to optimize the consonant vowel (CV) ratio in nonsense syllables was determined for stops and fricatives, both voiced and voiceless. Twelve children with congenital moderate to severe sensorineural hearing loss acted as subjects. One group of 6 children ranged in age from 5 to 6 years, a second group of 6 children were 8 to 9 years of age. The test stimuli consisted of VC nonsense syllables with various levels of enhancement. The enhancement levels ranged from 0 dB (for the unprocessed stimulus) to 30 dB of gain, in steps of 3 dB. The gain was applied to only the consonant portion of each nonsense syllable. The arc sine transformation was used to stabilize the error variance of the test scores. Curves were fitted to the transformed scores as a function of enhancement level. The maximum value of this curve identified the CV ratio at which consonant recognition was maximized for experimental condition and consonant type. The results showed that significant improvements in consonant recognition can be obtained with individualized adjustment of consonant amplitude for children as young as 5 year of age.