Many animals use sounds for communication, but few of them must learn the signals. Human beings, whales and dolphins, and some bats among mammals, and parrots, songbirds, and three other groups among birds, are the only animals that learn complex vocal signals. To learn vocalizations, animals, including humans, must hear their own voice because they must know if their utterances resemble the models to copy. Understanding the general principles of how auditory feedback is used to adjust vocal output in humans can be studied. The present proposal c6ntains several specific aims which attempt to answer questions about the role of auditory feedback in both the development of song in young birds and the maintenance of song in adult individuals. These studies use newly developed electronic methods of altering auditory feedback that birds hear. Birds hear both natural auditory feedback and delayed artificial feedback signals. Preliminary studies show that this type of perturbation induces dramatic changes in the song of adult zebra finches which are thought to be unable to change song in adulthood. Young birds memorize a tutor song before they can sing. They use the memory trace of the tutor song as a template to shape their own songs. It is hypothesized that young birds fail to reproduce the tutor song if auditory feedback is perturbed during song development. If normal auditory feedback is restored at some stage of song development, the birds are likely to redirect the direction of song development. The effects of feedback perturbation can be studied at the level of single neurons. Song control areas of the brain contain neurons that respond exclusively to the individual bird's own song. This selectivity emerges during song development. The study of these neurons should provide insights into the mechanisms of vocal learning. The question is whether these neurons lose their selectivity for the bird's own song when the song undergoes changes by feedback perturbation. If the neurons do not change their stimulus-selectivity, they and the neural circuits they represent do not retain plasticity. Finally, we will examine the important hypothesis that the anterior forebrain pathway of the song control system processes auditory feedback signals.