This research application focuses on whether cochlear-hearing loss has a detrimental effect on sound segregation, resulting in added difficulty discriminating between complex sounds. Two cues that may facilitate segregation of sound sources in normal-hearing listeners will be investigated: differences in temporal properties and different sound onsets. The program follows a model of auditory processing assuming that the auditory system first groups particular characteristics of sound to form "auditory objects." Once an object has been formed, different characteristics of that sound can be evaluated for identification, discrimination, etc. One particular aspect of sound, its spectral shape, is important to the understanding of speech, and the abilities of hearing-impaired listeners to segregate sounds for the purposes of spectral shape discrimination will be evaluated here. Listeners will be asked to detect changes in the spectral shape of a target sound in the presence of a distractor sound. Cues that encourage perceptual segregation will be manipulated to allow the auditory system to segregate the distractor from the target, thereby permitting clear spectral analysis of the target. If sound segregation occurs, the listener will be able to discriminate spectral shapes as if the distractor is not present. In contrast, sensitivity to spectral shape is likely to be poor if the target and distractor are not segregated. Various segregation cues will be manipulated and their effects on the ability to segregate competing sounds will be evaluated in listeners with normal and impaired hearing. Knowledge of how sounds can be segregated, especially in the presence of cochlear damage, may provide a better understanding of why people with hearing loss have difficulty recognizing speech in noisy environments containing multiple sound sources. Future work will be directed toward the cues that encourage good sound segregation, and therefore more normal analysis of spectral shape, to suggest new directions in amplification schemes.