The proposed experiments have been designed to provide information on the dynamic characteristics of auditory processing. There are two separate but related lines of research. The first is motivated, in part, by recent evidence that simultaneous pure-tone masking is time-varying and, as a result, that psychophysical measures of frequency selectivity sharpen during the first 100 to 150 ms of stimulation. The goals of the first line of research are to further our understanding of the mechanisms responsible for the temporal effect, to determine whether sensorineural hearing loss affects those mechanisms, and to determine to what extent those temporal effects play a role in the auditory processing of complex signals such as speech. Specific projects include further studies of temporal effects in pure-tone masking in normal-hearing subjects and in subjects with sensorineural hearing loss, and studies of temporal effects in masking by complex (including vowel and consonant-vowel) maskers in normal-hearing subjects. Among the hypotheses to be tested is that the mechanisms responsible for enhancing frequency selectivity over time in normal-hearing subjects are damaged in subjects with sensorineural hearing loss. The second line of research is motivated by the fact that hearing- impaired individuals typically have difficulty understanding speech in noisy environments. The goal of this research is to evaluate the hypothesis that at least some of that difficulty is due to an inability to detect the slow (amplitude) modulations in speech in the presence of a background noise, such as speech from a competing source. This line of research involves studying the masking of an amplitude-modulated signal by an amplitude- modulated masker in normal-hearing and hearing-impaired subjects. It is hoped that the results from the proposed studies will further our understanding of the mechanisms involved in dynamic auditory processing; further our understanding of the peripheral mechanisms involved in the deterioration of frequency selectivity in subjects with sensorineural hearing loss; and further our understanding of processing of complex signals such as speech.
