Project Summary Despite recent technological advances, people still suffer from communication difficulties that impact their professional, social, and family lives, as well as their mental health. People with sensorineural hearing loss (SNHL) struggle with understanding speech, particularly in noisy situations. In fact, people with similar degrees of clinically defined hearing loss can have a wide range of speech-recognition abilities, likely due to differences in underlying suprathreshold deficits that are hidden from current audiological assessment. Although a listener’s sensitivity to simultaneously spectrally and temporally modulated (STM) sounds is known to be predictive of speech-in-noise performance in individual listeners, the underlying mechanisms of this predictive power remain a topic of active debate. Physiological evidence from our lab and others demonstrate that several forms of SNHL (e.g., OHC and/or IHC dysfunction) affect within and across-channel modulation coding of signals in different ways. For example, distorted tonotopy due to OHC dysfunction can affect the perceptually relevant within- channel signal-to-noise ratio in the modulation domain, as well as across-channel temporal coherence of modulations that are useful for source segregation. Despite these clear and varied implications for modulation coding of signals, these effects are surprisingly understudied with respect to signal-in-noise coding, which is the focus of the proposed work. We use a cross-species experimental design to collect anatomical, single-unit AN-fiber, evoked-response, and diagnostic data from several pre-clinical chinchilla models of SNHL, as well as evoked-response, diagnostic, psychophysical, and speech-in-noise data from human listeners spanning a range of age and hearing status. Aim 1 is to characterize SNHL effects on within-channel modulation masking, where the data collected will test the hypothesis that OHC and IHC dysfunction each degrade the perceptually relevant neural modulation signal-to-noise ratio, but in distinct ways. Aim 2 is to characterize SNHL effects on across-channel temporal coherence cues, where the data collected will test the hypothesis that distorted tonotopy is prevalent in both animals and human listeners and has a perceptually relevant effect on peripheral across-channel temporal coherence. Aim 3 is to characterize SNHL effects on STM sensitivity, where our cross- species data will test the hypothesis that the predictive power of STM stimuli for speech-in-noise perception arises largely from distorted tonotopy and the effects of SNHL on temporal modulation coding, rather than from broadened tonotopic tuning or degraded temporal precision. Data will be harmonized in an open-source data- science framework to facilitate future causal modeling by us and others. Our unique ability to quantitatively synergize cross-species data within a rigorous perceptually relevant framework will allow us to test our general hypothesis that...