Reduction of formant bandwidth improves vowel identification with sensorineural impairment
Donald G. Jamieson, Curtis W. Ponton, Blas Espinoza-Varas · The Journal of the Acoustical Society of America · 1985
Accurate identification of front-back vowels depends on the ability to locate the peak of F2. Since hearing impairment reduces frequency resolution, sensorineural hearing impaired listeners often have difficulty with certain vowel distinctions. Espinoza-Varas, Jamieson, and Wahn [J. Acoust. Soc. Am. Suppl. 1 76, S80 (1984)] showed that (a) for normal listeners, equal changes in F2 frequency in critical-band units produce equal changes in the judged “goodness” of vowels on front-back vowel continua, cued by changes in F2; and (b) sensorineural impaired listeners are less sensitive to these F2 changes and less accurate in their identification of vowels. The present paper continues this work, examining whether vowel sounds can be altered to reduce masking between adjacent spectral frequencies, while preserving vowel quality. Following Assmann [J. Acoust. Soc. Am. Suppl. 1 76, S81 (1984)] we examined identification for synthesized vowels with normal versus narrow formant bandwidths. We also examined vowel identification performance for natural vowels which had been filtered to reduce formant bandwidths, while preserving the locations of the spectral peaks. Some hearing impaired listeners show significantly improved performance with these vowel sounds (for example, categorization functions for the synthesized vowel continuum /u/-/i/ become steeper). No listener showed poorer performance with the processed sounds. We conclude that (a) masking between adjacent spectral frequencies may cause hearing impaired listeners to make errors in vowel identification and (b) this masking can be reduced by processing speech signals to reduce formant bandwidth. [Work supported by grants from the AHFMR, HWCRDP, and NSERC.]