Tone-Glide Discrimination

Normal and Hearing-Impaired Listeners

Speech sounds vary rapidly in frequency, and the status of the auditory system might be expected to influence the processing of time-varying signals. Two experiments were undertaken to determine the effect of sensorineural hearing loss on the discrimination of frequency-varying sinusoids which are analogous to second formant transitions and contiguous steady-state portions of consonant-vowel and vowel-consonant syllables. A transformed up-down procedure was used to estimate the difference limen of the glide (transition) portions of the stimuli. In Experiment 1, it was found that three of the four normal hearers exhibited larger difference limens for stimuli with glides preceding fixed-frequency (steady state) portions than for comparable glide-following conditions. Subjects with sensorineural hearing loss did not show this effect consistently. In Experiment 2, the possibility of temporal masking of the glide segment by the fixed-frequency segment was explored. Large individual differences in temporal masking effects were observed for both normal-hearing and hearing-impaired subjects. Temporal masking could account for some, but not all of the differences in discriminability of glide-preceding and glide-following conditions. It appears hat audiometrically similar sensorineural hearing losses can differentially affect temporal masking and discrimination of the tone glides.

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