The neural mechanisms of auditory perception cannot be understood without detailed knowledge of physiological responses to sounds for which psychophysical responses are well described. This proposal presents a comprehensive approach to this important problem and focuses on the question of how information carried by amplitude modulations of complex sounds is encoded and processed by the brain. Despite recent advances in digital hearing-aid technology, our limited understanding of the neural mechanisms involved in processing complex sounds remains a significant limitation in our ability to aid listeners with hearing loss. New strategies to assist listeners with processing sounds in complex acoustic environments will emerge from our investigations of how the healthy auditory system handles this challenge. The three Aims of this proposal feature a novel combination of behavioral, physiological, and computational modeling approaches to address the problem of encoding and processing amplitude-modulated (AM) sounds. The 1st Aim will test three hypotheses concerning behavioral and psychophysical thresholds. The first hypothesis focuses on defining AM detection and discrimination thresholds for rabbits and humans and uses rigorously matched test procedures that are compatible with physiological approaches (Aim 2). The second hypothesis probes a long-standing puzzle: behavioral AM-detection thresholds improve as sound level increases, whereas single-unit physiological coding (based on current theories) degrades as level increases. The third hypothesis concerns the identification of detailed cues for masked AM detection. These cues will be identified with a novel application of reproducible maskers in the modulation domain. The 2nd Aim will test hypotheses of physiological AM coding at the level of the inferior colliculus (IC) in awake rabbit. These studies will include stimuli selected on the basis of behavioral results from Aim 1. We have developed new physiological methods for temporally precise recordings from populations of IC neurons using tetrodes. These recordings enable rigorous tests of the relative reliance of neural encoding on average discharge rates and temporal response patterns, including statistical analyses of spike rates and patterns across ensembles of neurons. The 3rd Aim uses computational techniques to test competing theories for AM-rate tuning in the IC. Recent models have proposed various neural mechanisms to explain AM responses in the midbrain. We will rigorously test these models and will include tests with stimuli other than those for which the models were designed. The results will explicitly determine which models are most consistent with our physiological data. These studies will advance our understanding of the mechanisms underlying AM coding and processing in the auditory system. This information will instruct efforts to enhance and restore critical aspects of complex sounds for listeners with hearing loss by improving hearing-aid signal-processing algorithms. The Public Health Relevance of this project is to determine how the healthy auditory system encodes complex sounds. We will use a novel combination of behavioral, physiological, and computer modeling approaches to identify how the brain encodes and extracts amplitude fluctuations in complex sounds. Because hearing loss in humans typically involves difficulty understanding complex sounds, knowledge of how the brain codes these ubiquitous sounds will provide new and important insights for aiding listeners with hearing loss.

National Institute of Health (NIH)
National Institute on Deafness and Other Communication Disorders (NIDCD)
Research Project (R01)
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Auditory System Study Section (AUD)
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Miller, Roger
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University of Rochester
Biomedical Engineering
Schools of Dentistry
United States
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Carney, Laurel H; Zilany, Muhammad S A; Huang, Nicholas J et al. (2014) Suboptimal use of neural information in a mammalian auditory system. J Neurosci 34:1306-13
Carney, Laurel H; Sarkar, Srijata; Abrams, Kristina S et al. (2011) Sound-localization ability of the Mongolian gerbil (Meriones unguiculatus) in a task with a simplified response map. Hear Res 275:89-95
Wojtczak, Magdalena; Nelson, Paul C; Viemeister, Neal F et al. (2011) Forward masking in the amplitude-modulation domain for tone carriers: psychophysical results and physiological correlates. J Assoc Res Otolaryngol 12:361-73
Zilany, Muhammad S A; Carney, Laurel H (2010) Power-law dynamics in an auditory-nerve model can account for neural adaptation to sound-level statistics. J Neurosci 30:10380-90
Gai, Yan; Carney, Laurel H (2008) Statistical analyses of temporal information in auditory brainstem responses to tones in noise: correlation index and spike-distance metric. J Assoc Res Otolaryngol 9:373-87
Gai, Yan; Carney, Laurel H (2008) Influence of inhibitory inputs on rate and timing of responses in the anteroventral cochlear nucleus. J Neurophysiol 99:1077-95
Deshmukh, Om D; Espy-Wilson, Carol Y; Carney, Laurel H (2007) Speech enhancement using the modified phase-opponency model. J Acoust Soc Am 121:3886-98
Nelson, Paul C; Ewert, Stephan D; Carney, Laurel H et al. (2007) Comparison of level discrimination, increment detection, and comodulation masking release in the audio- and envelope-frequency domains. J Acoust Soc Am 121:2168-81
Calandruccio, Lauren; Doherty, Karen A; Carney, Laurel H et al. (2007) Perception of temporally processed speech by listeners with hearing impairment. Ear Hear 28:512-23
Nelson, Paul C; Carney, Laurel H (2007) Neural rate and timing cues for detection and discrimination of amplitude-modulated tones in the awake rabbit inferior colliculus. J Neurophysiol 97:522-39

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