Stochastic undersampling steepens auditory threshold/duration functions: implications for understanding auditory deafferentation and aging

Abstract

It has long been known that some listeners experience hearing difficulties out of proportion with their audiometric losses. Notably, some older adults as well as auditory neuropathy patients have temporal-processing and speech-in-noise intelligibility deficits not accountable for by elevated audiometric thresholds. The study of these hearing deficits has been revitalized by recent studies that show that auditory deafferentation comes with aging and can occur even in the absence of an audiometric loss. The present study builds on the stochastic undersampling principle proposed by Lopez-Poveda and Barrios (2013) to account for the perceptual effects of auditory deafferentation. Auditory threshold/duration functions were measured for broadband noises that were stochastically undersampled to various different degrees. Stimuli with and without undersampling were equated for overall energy in order to focus on the changes that undersampling elicited on the stimulus waveforms, and not on its effects on the overall stimulus energy. Stochastic undersampling impaired the detection of short sounds (<20 ms). The detection of long sounds (>50 ms) did not change or improved, depending on the degree of undersampling. The results for short sounds show that stochastic undersampling, and hence presumably deafferentation, can account for the steeper threshold/duration functions observed in auditory neuropathy patients and older adults with (near) normal audiometry. This suggests that deafferentation might be diagnosed using pure-tone audiometry with short tones. It further suggests that the auditory system of audiometrically normal older listeners might not be “slower than normal”, as is commonly thought, but simply less well afferented. Finally, the results for both short and long sounds support the probabilistic theories of detectability that challenge the idea that auditory threshold occurs by integration of sound energy over time.

Synaptopathy in the Aging Cochlea: Characterizing Early-Neural Deficits in Auditory Temporal Envelope Processing

“…However, partial deafferentation caused by cochlear synaptopathy may cause additional deficits in early neural coding due to stochastic undersampling of sounds by the auditory nerve (Lopez-Poveda and Barrios, 2013;Lopez-Poveda, 2014). Aging and noise exposure may be especially affected by this stochastic undersampling (Marmel et al, 2015) because the low-spontaneous-rate neurons first targeted with aging (Schmiedt et al, 1996) show a greater preference for synchronized firing to AM sounds at moderate to high levels (Joris and Yin, 1992). EFRs are a noninvasive assay to measure these temporal processing deficits and provide complementary information to the ABRs, which are dominated by onset responses (Parthasarathy et al, 2014;Bidelman, 2015).…”

The search for noise-induced cochlear synaptopathy in humans: Mission impossible?

“…• Testing audiometric thresholds for brief tones (<20ms) has been suggested as a possible method for detecting synaptopathy. Theoretical reasoning by Lopez-Poveda and Barrios (2013) and perceptual model simulations by Marmel et al (2015) suggest that synaptopathy involves a substantial loss of low-threshold AN fibers in addition to the larger loss of high-threshold fibers, which is predicted to elevate the detection threshold for brief tones, without significantly elevating the thresholds for longer sounds. The results of Wong et al (2019) in the budgerigar undermine this approach and the experimental data currently available are not adequate to allow a recommended protocol for this test.…”

A Computational Model of Thalamocortical Dysrhythmia in People With Tinnitus

“…It should be noted that the y-axis in each graph is scaled relative to the overall % loss in each case and is therefore different for each case. Analytical analysis of the findings presented in [3] has been explored in [4].…”

“…The functional impact of high spontaneous fibre loss is reflected in reduced auditory sensitivity to soft sounds whilst low-and medium-spontaneous fibre loss is reflected by a reduced sensitivity in deafferented frequencies [4]. Tinnitus related studies have shown evidence of cochlear synaptopathy using auditory brainstem response (ABR) [5], [6] (Figure 1).…”