Occlusive silence duration of voiceless intervocalic plosives and voicing perception by normal and hearing-impaired...

The duration of occlusive silence of intervocalic unvoiced plosives is one of several acoustic cues contributing to the correct identification of voicelessness for normally hearing subjects. In a previous investigation on one velar plosive, some hearing-impaired subjects required an abnormally long duration of its occlusive silence in order to avoid voicing confusions. The present study investigated whether this would occur for the different plosives in various intervocalic contexts and for male and female voices.

Speech signals from a male and a female voice pronouncing the three voiceless plosives (p,t,k) in three different vocalic contexts (a,i,u) were recorded. Each of these 18 vowel-consonant-vowel (VCV) utterances was edited to obtain a series of tokens with occlusive silence durations varying from 0 to 180 msec. Phonetic identification of these tokens was assessed for seven normally hearing persons and for seven subjects with a sensorineural hearing loss.

For the various VCVs, about half of the hearing impaired subjects required abnormally long occlusive silence durations to avoid voicing confusions. For normal as well as hearing-impaired subjects duration thresholds varied considerably and not systematically for the different VCVs. The amount of voicing confusions tended to be related to audiogram loss.

For hearing-impaired subjects, a normal occlusive silence duration can lead to voicing misperceptions for the various plosives in different vowel contexts and for male and female voices. The large variability in the results of each subject for the different VCVs indicates that even a strong anomaly in temporal perception, which certainly underlies a need for abnormally long occlusive silence duration, did not systematically overrule voicing perception.