Arthur Boothroyd
Bethany Mulhearn
Juan Gong
Jodi Ostroff
City Univ. of New York, 33 W. 42 St., New York, NY 10036
Phoneme and word recognition, was measured in seven hearing adults under various conditions of spectral smearing---produced by multiplying the speech waveform by low-pass-filtered noise. Phoneme recognition fell from 97% for no smearing to 13% for complete smearing ((plus or minus)10 kHz). Smearing by (plus or minus)600 Hz reduced group mean phoneme recognition to 50%---a score typical of hearing-impaired subjects with hearing losses around 80 dB, listening to amplified speech. In a second experiment, noise was mixed with the speech before spectral smearing was introduced. Noise susceptibility was measured as the S/N ratio required for a phoneme recognition score that was 50% of the score in quiet. Smearing at (plus or minus)1 kHz increased noise susceptibility by 20 dB, an amount similar to that found in hearing-impaired subjects with losses in excess of 90 dB. As with hearing-impaired subjects, spectral smearing diminished the perception of consonant place more than the perception of consonant manner and voicing. Unlike with hearing-impaired subjects, however, smearing affected vowel perception more than consonant perception. This last finding may be attributed to the use smearing over a fixed bandwidth---producing a greater percentage smearing in the lower frequencies. [Work supported by NIDCD Grant No. 10078.]