Spectral cues to perception of /d, n, l/ by normal- and impaired-hearing listeners

The alveolar consonants /d, n, l/ occur frequently in intervocalic position in conversational speech but have received little study for differences in their acoustic cues. Impaired- and normal-hearing listeners were investigated for use of consonant-segment versus transition-segment cues to recognition of /d, n, l/ in /aeCae/ tokens extracted from sentences. To examine the cues' contribution to /d, n, l/ recognition, the segments were degraded singly or in combinations in the tokens as follows: [aeC] or [Cae] transitions were replaced by adjacent pitch periods from the respective vowels; the consonant segments were replaced by silence or by a synthetic consonant approximating the summed low-frequency spectra of the /d, n, l/ murmurs. The results with normal-hearing listeners showed that the presence of any one of the three segments, [aeC] transition, [Cae] transition, or natural consonant segment, supported a moderate to high level of /d, n, l/ recognition, depending on the phoneme. In contrast, the severely hearing-impaired listeners' consonant recognition was poor on the basis of transition information, but better in the presence of the natural consonants. The /aeCae/'s with the synthetic consonant yielded chance level performance for the hearing-impaired listeners but good consonant recognition for the normal-hearing listeners--a further indication that cues in the transitions were quite useful for the normal-hearing group but not for the hearing-impaired group.