The long-term goal of the proposed work is to improve our understanding of the neural representation of speech in the presence of sensorineural hearing loss. Single neuron recordings will be made in cats exposed to intense noise, which produces a hearing loss comparable to moderate high frequency loss (greater than or equal to 1 kHz). The first aim is designed to test and further develop a way of compensating for the loss of sharp cochlear tuning and nonlinear suppression in damaged cochleas. The aim is to develop a method of specifying the optimum spectral shape for presenting a particular speech sound to an ear with a particular hearing loss, where optimum means designed to produce patterns of auditory nerve activity that are as normal as possible. The second aim will characterize neural responses to running speech, instead of the isolated phonemes that are usually used in auditory experiments. The representation of sentence-level speech will be characterized in both the spectral and temporal domains, for both normal and damaged ears. The compensation methods developed in the first aim will be tested using these stimuli. The effects of background noise will also be examined. In the third aim, an accurate computational model of auditory nerve activity in a damaged ear will be developed. Development and testing of the model will be closely coordinated with the experimental studies of the first two aims. The goal is to produce a model which is accurate enough to be used as a test bed for developing hearing-aid signal- processing. The final aim will study how cats with a hearing loss discriminate variants of the vowel /epsilon/ with different second formant frequencies. These behavioral experiments are designed to differentiate between two models of information representation in the auditory nerve, the so-called rate-place, and temporal-place models. The experiments take advantage of the fact that cats with a moderate hearing loss do not have rate-place information which would allow them to discriminate these vowels. This aim will provide evidence, for the first time, on the relative importance of the two information representation codes in the auditory nerve and will be important in interpreting the results of the experiments in the other three aims.