Psychoacoustic and phonetic temporal processing in normal and hearing-impaired listeners

Abstract

Four measures of auditory temporal processing were obtained from 16 normals and 16 individuals with a hearing loss of heterogeneous origin. These measures were: (1) temporal integration—the difference in detection thresholds between signals of 10- and 1000-ms duration (which was determined to provide an estimate of the ability to integrate energy over time), (2) gap detection—the shortest duration of silence between two noise bursts that can be discriminated from an uninterrupted noise, (3) temporal difference limen—the increment in duration necessary to detect a difference in the duration of a noise burst, (4) gap difference limen—the increment in duration necessary to detect a difference in the duration of a silent interval between two noise bursts. Each measure was obtained for stimuli centered both at 500 and at 4000 Hz using a three-alternative forced-choice procedure. In addition, measures of identification and discrimination were obtained for two sets of synthetic speech syllables varying chiefly in a temporal parameter, voice-onset-time, from /ba/ to /pa/ and from /bi/ to /pi/. Finally, speech identification in noise was measured with the FAAF test. Most of the hearing-impaired listeners displayed poorer temporal analysis than the normals on all of the psychoacoustical tasks, regardless of whether the two groups were compared at similar sound pressure levels or at similar sensation levels. Although the hearing-impaired listeners displayed a reduction in the ability to discriminate subphonemic cues for the voiced–voiceless distinction, their identification of that distinction in stop consonants appeared to be normal. The hearing-impaired group made about twice as many errors as did the normals on each of the consonant features of place, manner, and voicing when identifying speech in noise. Increased temporal difference limen and longer gap-detection thresholds were found to correlate significantly with reduced speech intelligibility in noise, even when the effects of the pure-tone threshold loss were partialed out.