DESCRIPTION: The long-range goals of the proposed research are to further our understanding of the mechanisms underlying the auditory processing of time-varying stimuli, and to determine how those mechanisms are affected by sensorineural hearing loss. There are two separate but related lines of research. The first line focuses on the detection of brief signals as a function of prior masker stimulation. The underlying mechanisms could play an important role in enhancing newly arriving or intermittent signals, especially those in an on-going background. The temporal effect in simultaneous masking is called the "temporal course of masking" when it occurs with off-frequency tonal maskers, and "overshoot" when it occurs with broadband noise maskers. The goals of the first line of research are to (1) gain a better understanding of the processing underlying these two temporal effects, and in particular to test a newly proposed theory that unifies the temporal course of masking and overshoot, and (2) further our understanding of the effects of sensorineural hearing loss on temporal effects in simultaneous masking. The second line of research concentrates on the processing of amplitude modulation. The temporal complexity of these experiments is relevant to the auditory processing underlying the perception of everyday complex sounds such as speech or music. The goals of the second line of research are to (1) further our understanding of how the auditory system processes amplitude modulation in the presence of competing modulation, and to determine to what extent such processing is occurring within a single auditory channel, (2) gain insight into the mechanisms responsible for the recently described effect of frequency on within-and across-channel temporal resolution, (3) relate the processing of amplitude modulation to the processing of speech in time-varying backgrounds, and (4) further our understanding of why individuals with a sensorineural hearing loss often have particular difficulty understanding speech in temporally complex backgrounds.