PROJECT SUMMARY/ABSTRACT The healthy auditory system processes and ultimately makes sense of complex dynamic sounds that vary spectrally and temporally. This complicated process allows for human and non-human species to communicate in both quiet and noisy environments. Significant advances in the understanding of spatiotemporal processing has come from human behavioral studies and physiological animal experiments using frequency sweep stimuli, which are sounds that glide upwards or downwards with frequency over time. Human behavioral data shows that up-sweeps are substantially more effective at masking a tone compared to down-sweeps (> 20 dB). The behavioral literature attributes the dependence on sweep direction to cochlear dispersion, which involves variations in the shape of the basilar membrane (BM) waveform generated by each masker. Due to dispersion, the BM waveform for the down-sweep is peakier compared to the broader response of the up-sweep. Consequently, the presence of a down-swept masker allows for easier detection of the signal in the dips of its waveform. This interpretation finds support in animal measurements and physiological models. While the dispersion mechanism has been used to explain the masking effects between upward and downward sweeps, recent measurements of cochlear vibration in mouse also reveal differences in the cochlear suppression produced by upward and downward swept suppressors and these differences are dependent on sweep rate. Suppression is thought to be important for auditory tasks such as understanding speech in noisy environments. Similar measures of suppression using up- and down-swept stimuli have not been conducted in humans, nor have the suppression effects been compared to behavioral masking. Furthermore, although human behavioral experiments have shown masking differences for upward and downward swept maskers over a range of sweep rates, none of these studies explored what I hypothesize are perhaps the most interesting range of rates (i.e., sweep rates similar to the velocity of the BM traveling wave or to frequency transitions in speech). The proposed aims use a combination of behavioral and otoacoustic measures to study the effects of sweep rate and direction using swept stimuli as either behavioral maskers or otoacoustic suppressors. Otoacoustic emissions are advantageous as they provide a powerful, non-invasive measure of outer hair cell function, enabling the study of suppression effects in humans and their correlation to behavioral masking. The study will pursue the following aims: 1) Determine the strength of behavioral masking as a function of sweep rate and direction, and 2) Determine the strength of cochlear suppression as a function of sweep rate and direction. Completion of the proposed aims will advance understanding of the role of suppression in processing dynamic sounds that vary in rate and direction. The results may provide a framework for studying how this process is impacted with i...