This research represents the beginning of an investigation into auditory temporal resolution in normal-hearing and hearing-impaired subjects. The proposed project will compare the temporal resolution of stimuli that change rapidly in amplitude with the temporal resolution of stimuli that change rapidly in frequency. Previous research on temporal resolution has used amplitude-varying signals almost exclusively, although information is coded in the speech signal by both types of variation, as in the noise bursts of stop consonants. The purpose of the study is to determine the extent to which the two types of signals are governed by a common underlying mechanism and the extent to which such a mechanism or mechanisms are disrupted by hearing loss. The temporal resolution of amplitude-varying signals will be measured with a gap detection task. Gap thresholds for sinusoidal stimuli will be obtained at a range of levels and, frequencies from normal-hearing and hearing-impaired subjects. The temporal resolution of frequency-varying signals will be measured with a step-detection task in which the subjects will be asked to discriminate between two frequency-modulated sinusoids. One signal is a glide. the other is identical to the glide except that its trajectory follows a series of discrete steps in frequency, remaining at one frequency for a few milliseconds and then jumping almost instantaneously to another. As the number of steps increases, the step signal gradually becomes indistinguishable from the glide, because the duration of the individual steps is too brief to be resolved by the listener.The step duration at this point is referred to as the step-detection threshold. Comparison of the gap- and step-detection thresholds will be aimed at answering the following experimental questions: (1) does the temporal resolution of amplitude changes and frequency changes differ, and (2) is temporal resolution poorer in hearing-impaired persons than in normal-hearing individuals.
