Voicing perception for final stops was studied for impaired- and for normal-hearing listeners when cues in naturally spoken syllables were progressively neutralized. The syllables were ten different utterances of /daep, daek, daet, daeb, daeg, daed/ spoken in random order by a male. The cue modifications consisted progressively of neutralized vowel duration, equalized occlusion duration, burst deletion, murmur deletion, vowel-transition interchange, and transition deletion. The impaired subjects had moderate-to-severe losses and showed at least 70% correct voicing for the unmodified syllables. For the voiced stops, vowel-duration adjustment and murmur deletion each resulted in significant reductions in voicing perception for more than one-third of the impaired listeners; all normals showed good performance following neutralization of these cues. For the voiceless stops, large percentages of both listener groups showed decreased voicing perception due to the burst deletion, though a majority of both groups performed well above change even after the vowel-duration adjustment and the burst deletion. When the vowel off-going transitions were exchanged between cognate syllables in given pairs, the effect on voicing perception exhibited by many impaired- and all normal-hearing listeners implicated the vowel transitions as an important additional source of cues to final-stop voicing perception.

In an earlier study on hearing for formant transitions, we found differences in the discrimination of transition tempo (rate of frequency change) as a function of the frequency-size of transitions which were rising to a steady state. In the present study tempo discrimination was measured for transitions that differed in temporal position and in frequency direction relative to a steady-state phase. Nineteen hearing-impaired and five normal-hearing listeners discriminated transition tempo in a 3IFC response paradigm. The transitions were initial or final, and were rising or falling in frequency, with reference to the steady-state frequency. For transitions covering the same frequency range (e.g., transitions of 100 Hz to or from a 1000-Hz steady state), tempo discrimination was better for initial transitions than for final. Better transitions of different frequency-directions, but sharing the same position relative to the steady-state (e.g., final transitions downward in frequency from 1000 to 900 Hz versus upward in frequency from 1000 to 1100 Hz) tempo discrimination was better for the transitions downward in frequency. Hearing-impaired listeners showed poorer mean transition-tempo discrimination than normal-hearing listeners; marked individual differences occurred in both groups.

The effects on voicing identification of progressive neutralization of the voicing cues was examined further (99th ASA meeting, Paper GG6). Cue modifications were digital deletions or iterations performed on ten voicing-cognate pairs of token syllables, spoken in a randomized list of 10× the set: dap, dak, dat, dab, dag, dad. The cue modifications consisted progressively of neutralized vowel durations, equalized closure duration, burst deletion, murmur deletion, and transition deletion. For voiced-consonant syllables, about half of the 25 hearing-impaired were sensitive to vowel duration and the presence of transitions; some of these listeners and others were sensitive to the presence of the burst and/or murmur. For syllables with unvoiced consonants, vowel duration and the presence of release burst affected identification for about half of the hearing impaired. Among the remaining impaired listeners, sensitivity varied unsystematically as a function of burst presence and/or transition deletion. Normal listeners appeared generally to make use of the transition cues more than did the hearing impaired. [Work supported in part by the U. S. Public Health Service.]

Further work will be presented on voicing cues, specifically for initial stops, used by the hearing-impaired. The set of test syllables /pæd, kæd, tæd, bæd, gæd, dæd/ was randomized 10 times on a list recorded by a male. Based on acoustical analyses, the potential sources of voicing cues in the syllables were: release-burst duration, transition-pattern of vowel onset, and vowel pitch. Among different conditions these cues in the syllables were modified cumulatively, so as to eliminate the contribution to voicing of each cue. The modifications were made through LPC resynthesis and/or waveform deletions. The conditions were administered monaurally at comfortable levels to six normal- and 21 impaired-hearing adults. The syllables of each condition were presented in single-interval identification trials without feedback. Generally, a similar pattern of results was seen between the impaired and the normal groups, although the impaired group performed somewhat poorer. Perception of initial stop voicing was unaffected by equalized vowel pitch. For voiceless stops deletion of the release burst reduced voicing perception for most listeners. However, for voiced stops the burst deletion worsened performance for less than half of the listeners. When the voiced burst and vowel-onset-transitions were removed, voicing perception was reduced for most listeners.

Impaired- and normal-hearing subjects (Ss) identified the pitch of either a low-, mid-, or high-frequency noise burst in a recognition-masking task with a two-formant vowel masker which preceded and/or followed the noise burst. F1 of the vowel was at 700 Hz and F2 at 1100 Hz. The three noise bursts were bands of flat-spectrum noise: 500–1500 Hz, 1500–4000 Hz, or 4000–6000 Hz. Forward-, backward-, and combined-forward-and-backward-masking conditions were tested with a 10 ms Δt. The vowel was presented at most comfortable listening level (MCL) for the impaired and at 90 dB SPL for the normal-hearing Ss: the noise bursts were presented at 10 dB SL. Pitch recognition of the noise bursts was affected least in the backward-masking condition and was poorest in the combined-forward-and-backward-masking condition. In the combined masking condition nearly all Ss showed some masking of pitch recognition for one or more of the noise bursts. Masking occurred most often for the low-frequency burst and least often for the high-frequency burst. Generally, release from masking was seen when Δt was lengthened to 100 ms.