Project Summary Realizing the potential of otoacoustic emissions (OAEs) as noninvasive probes of cochlear function requires understanding the physical and physiological mechanisms that generate and shape these sounds. To address important unresolved issues of cochlear mechanics while improving our understanding of OAE generation, we propose three aims involving innovative theoretical modeling rigorously tested by experimental measurements. The first Aim studies the action of ?suppressor? tones on OAE generation by testing the hypothesis that suppressors can both reduce the strength of existing OAE sources and create new sources of wave reflection within the cochlea. We determine whether suppressors can accurately map out the distribution of OAE generators in models where the distribution is known in advance and test whether eliminating sources created by the suppressor can improve the measurement of cochlear frequency selectivity using OAE suppression tuning curves. The second Aim studies the nature of the micromechanical irregularity believed necessary for the generation of reflection-source OAEs. We test whether efferent-induced changes in OAEs can be explained by the hypothesis that activation of medial olivocochlear (MOC) efferents alters the spatial pattern of irregularity. Using both measurements and models, we also explore the hypothesized but previously unrecognized role of irregularity on the generation of distortion-source OAEs and its modulation by contralateral acoustic stimulation. The third Aim explores the micromechanics of cochlear wave amplification and its consequences for OAE generation. Modeling work studies OAE generation in models incorporating forms of spatial feed-forward/backward amplification suggested by the oblique geometry of the outer hair cells. We also combine state-of-the-art measurements of organ of Corti vibration using optical coherence tomography (OCT) with theoretical inverse methods to study how the assumed coupling between the modes affects the generation and propagation of OAEs. Completion of these Aims will significantly enhance our understanding of OAE generation and its relationship to cochlear mechanics. The Aims are also directly relevant to improving the power of OAE-based diagnostics and other technological applications?such as hearing aids and preprocessors for speech-recognition devices?that benefit from knowledge of cochlear amplification, nonlinearity, and signal processing.