Effects of Signal Level and Spectral Contrast on Vowel Formant Discrimination for Normal-Hearing and Hearing-Impaired Listeners

Abstract

Purpose The aim of this study was to determine whether increasing the overall speech level or the individual spectral contrasts of vowel sounds can improve vowel formant discrimination for listeners both with and without normal hearing. Method Thresholds of vowel formant discrimination were examined for the F2 frequencies of 3 American English vowels for listeners with and without normal hearing. Spectral contrasts of the F2 were enhanced by 3, 6, and 9 dB. Vowel stimuli were presented at 70 and 90 dB SPL. Results The thresholds of listeners with hearing impairment were reduced significantly after spectral enhancement was implemented, especially at 90 dB SPL, whereas normal-hearing listeners did not benefit from spectral enhancement. Conclusion These results indicate that a combination of spectral enhancement of F2 and high speech level is most beneficial to improve vowel formant discrimination for listeners with hearing impairment.