Jacques Grange1, John Culling1 
School of Psychology, Cardiff University, Cardiff, United Kingdom

Pathologies underlying sensorineural hearing loss (SNHL) cannot yet all be differentially diagnosed. We are developing means of pathology discrimination with an advanced SNHL simulator. The physiologically inspired model of the auditory periphery (MAP, Meddis et al., 1986~2018) simulates stimulus encoding at the auditory nerve (AN) level through the firing patterns of 30,000 fibers arranged across 30 best frequencies (56 Hz to 8 kHz) and 3 spontaneous rates. Such encoding is then decoded/converted back into an acoustic signal to be presented to young, normally hearing listeners in psychophysical tasks. Simulator validation was obtained with a speech-in-noise intelligibility task for which simulated-normal-hearing speech reception thresholds (SRTs) were just 1 dB higher than those obtained for unprocessed stimuli. By inserting specific pathologies in the model, we believe one can reveal their psychophysical signatures. We first demonstrated the importance of efferent reflexes to the faithful coding of the temporal modulations that carry speech information. With both reflexes disabled, SRTs grew by 3-4 dB. Simulated AN rate-level functions illustrate how efferent reflexes enable the AN dynamic-range adaptation to context level that prevents information loss. While deactivating 70% of AN fibers or halving the endocochlear potential (EP) did not lead to any appreciable SRT inflation, total outer haircell (OHC) knockout led to a smaller SRT inflation than that found when efferent reflexes were disabled. Circa 90% general deafferentiation was required to reflect performance found in hearing impaired listeners, an outcome consistent with stochastic under-sampling predictions by Lopez-Poveda and Barrios (2013). Both ITD discrimination and MAA thresholds exhibited near-linear growth with the log of remaining efferent fibers. With decreasing EP or OHC count, SRTs inflated and dip-listening and F0-segregation benefits decreased. However, such benefits did not decrease with up to 96% deafferentation, despite SRT inflation. Overall, our simulator paves to way to enabling differential diagnosis of SNHL.

Acknowledgements: This work was funded by EPSRC.