Ninety percent of hearing loss occurs due to the loss of hair cells or auditory nerve cells. We now know that fish, amphibians and birds are able to grow new hair cells after the insult. Birds are the only animals that exhibit both hair cell regeneration and vocal learning, making them a unique model for aspects of human hearing impairment. Although long-term regeneration of hair cells in mammals appears feasible in the near future, questions remain about the functionality of these regenerated hair cells beyond basic audiograms. The consequences of hearing loss on human speech and language are devastating, both in children and adults. Here we investigate the effects of regenerated hair cells in an animal system whose complex vocal repertoire is learned and maintained through hearing. In the proposed research, we ask whether auditory perception is fully restored after hair cell regeneration in birds. This proposal continues two lines of investigation from previous periods of the project. One area of ​​research has investigated the basic mechanisms and simple perceptual consequences of acquired hearing loss and recovery. Now let's analyze the effects on higher-level perception. Past work on this grant shows that in addition to hair cell regeneration, birds also appear to regain much of their hearing abilities, including discrimination, recognition, and the production of learned vocalizations (Dooling et al., 1997). However, the human clinical literature is replete with patients presenting with normal audiograms but poor speech recognition, especially in noisy environments (Kujawa & Liberman, 2009). The exact etiology of these perceptual deficits is still unclear. Using avian models, we hope to shed light on some of the causes that could lead to improved clinical… half of the article… ration using three masking approaches: energetic, “chatty” and informational. These experiments attempt to directly model aspects of the human clinical problem of hearing-impaired and cochlear implant patients who have near-normal thresholds with amplification but still show poor speech understanding in noisy environments. Specific objective 3. To explore possible improvements in hair cell damage/hearing in birds with hereditary developmental high-frequency hearing loss and continued hair cell proliferation. BW canaries transiently increase hair cell proliferation after noise exposure (Gleich et al., 1997) and show improved hearing after ototoxic insult and recovery (Dooling et al., Submission). Here we intend to further investigate how regenerative mechanisms play a role in restoring hearing and whether it is possible to completely “cure” hearing loss in BW canaries..