PROJECT SUMMARY Pitch and harmonicity play a defining role in the perception of speech and music, and are crucial for the perceptual organization of sounds in an auditory scene. Listeners with hearing loss, and especially those with cochlear implants, suffer from a striking deficit in pitch perception abilities, as current sound processing strategies are unable to provide robust pitch cues. This lack of pitch cues is a major factor in their inability to perceive speech in noise, or in the case of cochlear implant usserss, perceive music. Despite advances in our understanding of how pitch is perceived, coded, and represented in our auditory system, there are still significant gaps in our basic understanding of how pitch, and especially harmonicity, is represented in the auditory cortex. A better understanding of the neural transformations involved in pitch perception should help in designing more effective neural and acoustic prostheses. The overall goal of the proposed project is to understand the neural representation of pitch and harmonicity and elucidate the role of temporal integration and harmonicity in pitch perception using a combination of behavioral (psychoacoustics) and neuroimaging techniques (fMRI). In the requested extension period, I propose to finish two projects related to both of these overarching themes. fMRI will be used to investigate what properties of harmonic complex tones are represented in anterior-lateral regions of auditory cortex. Using carefully controlled stimuli, this study should provide strong evidence for whether harmonic tones elicit a stronger response than inharmonic tones in auditory cortex. This would help elucidate the presence (or absence) of an integrated ‘pitch center’ in auditory cortex that is selectively responsive to the pitch of complex sounds. I will also finish conducting a series of behavioral experiments using a novel stimulus that produces an illusory virtual pitch percept, to provide empirical data for quantifying the parameters governing temporal integration in the perception of pitch. These behavioral experiments will add crucial understanding of the temporal aspects of pitch perception, which are not taken into account in current pitch perception models. The results of these experiments will also be extended by the studies planned for the R00 portion of the grant. Overall, the projects completed in this extension period will relate perceptual characterizations of the illusory stimulus to neurophysiological findings to provide new insights to the field of pitch perception, which in turn could motivate the development of novel pitch processing strategies in auditory prostheses. The research performed and training provided during this extended time period will enable me to achieve the goal of developing an independent research program that employs both neurophysiological and behavioral approaches to investigate auditory phenomena.