PLACE AND TIME PROCESSING OF PITCH IN THE CONTEXT OF COCHLEAR DYSFUNCTION

Sensorineural hearing loss occurs in 15% of American adults and current treatment protocols are often guided by limited and outdated diagnostics. Not all types of sensorineural hearing loss are identical in physiology, and a major priority of current auditory research is to innovate in the space of precision auditory diagnostics and treatments. Understanding how specific patterns of damage to the cochlea or auditory nerve vary in affecting the perception of different sounds is critical to improve treatments for hearing-impaired individuals. A history of auditory research has led to considerable insight as to how the anatomic components of the auditory periphery, namely inner hair cells (IHCs), outer hair cells (OHCs), and the cochlear synapse function together to transduce, amplify, and code simple sounds. However, there exist considerable gaps in our knowledge of how these peripheral components are responsible for maintaining the fidelity of more complex auditory phenomena and perception. Pitch, the perceived "highness" or "lowness" of a given sound, is an example of a complex psychoacoustic phenomenon. Pitch cues are used to listen to and compose music, process vowels, identify talkers, and convey emotion. Without intact pitch perception, conversation becomes emotionless, a symphony becomes a cacophony. Pitch perception tends to degrade with hearing loss, but in ways that are complex and not always predictable by current audiological diagnostics. Using a combination of neural metrics in both humans and chinchillas, we explored potential cochlear deficits that could underlie alterations in tonotopic and temporal representation of pitch. In chinchillas, we observed that disrupted place cues, likely through OHC damage and dysfunction, lead to an over-representation of envelope and poorer harmonic resolvability. IHC damage degrades the temporal envelope coding that is important for pitch perception derived from higher-order, unresolved harmonics. In humans, these consequences were directly linked to poorer pitch discrimination of resolved and unresolved harmonics, respectively. Indeed, this cross-species approach revealed significant insights into the physiological mechanisms underlying pitch processing by the auditory periphery and how they are affected by various subtypes of sensorineural hearing loss.