Fusion of dichotic consonants in normal-hearing and hearing-impaired listeners

Abstract

Hearing-impaired (HI) listeners have been shown to exhibit increased fusion of dichotic vowels, even with different fundamental frequency (F0), leading to binaural spectral averaging and interference. To determine if similar fusion and averaging occurs for consonants, four natural and synthesized stop consonants (/pa/, /ba/, /ka/, /ga/) at three F0s of 74, 106, and 185 Hz were presented dichotically—with ΔF0 varied—to normal-hearing (NH) and HI listeners. Listeners identified the one or two consonants perceived, and response options included /ta/ and /da/ as fused percepts. As ΔF0 increased, both groups showed decreases in fusion and increases in percent correct identification of both consonants, with HI listeners displaying similar fusion but poorer identification. Both groups exhibited spectral averaging (psychoacoustic fusion) of place of articulation but phonetic feature fusion for differences in voicing. With synthetic consonants, NH subjects showed increased fusion and decreased identification. Most HI listeners were unable to discriminate the synthetic consonants. The findings suggest smaller differences between groups in consonant fusion than vowel fusion, possibly due to the presence of more cues for segregation in natural speech or reduced reliance on spectral cues for consonant perception. The inability of HI listeners to discriminate synthetic consonants suggests a reliance on cues other than formant transitions for consonant discrimination.