Auditory deafferentation, or permanent loss of auditory nerve afferent terminals, occurs after noise overexposure and aging and may accompany many forms of hearing loss. It could cause significant auditory impairment but is undetected by regular clinical tests and so its effects on perception are poorly understood. Here, we hypothesize and test a neural mechanism by which deafferentation could deteriorate perception. The basic idea is that the spike train produced by each auditory afferent resembles a stochastically digitized version of the sound waveform and that the quality of the waveform representation in the whole nerve depends on the number of aggregated spike trains or auditory afferents. We reason that because spikes occur stochastically in time with a higher probability for high- than for low-intensity sounds, more afferents would be required for the nerve to faithfully encode high-frequency or low-intensity waveform features than low-frequency or high-intensity features. Deafferentation would thus degrade the encoding of these features. We further reason that due to the stochastic nature of nerve firing, the degradation would be greater in noise than in quiet. This hypothesis is tested using a vocoder. Sounds were filtered through ten adjacent frequency bands. For the signal in each band, multiple stochastically subsampled copies were obtained to roughly mimic different stochastic representations of that signal conveyed by different auditory afferents innervating a given cochlear region. These copies were then aggregated to obtain an acoustic stimulus. Tone detection and speech identification tests were performed by young, normal-hearing listeners using different numbers of stochastic samplers per frequency band in the vocoder. Results support the hypothesis that stochastic undersampling of the sound waveform, inspired by deafferentation, impairs speech perception in noise more than in quiet, consistent with auditory aging effects.
Keywords: auditory deafferentation, auditory aging, hearing loss, stochastic sampling, model, vocoder, information theory
Citation: Lopez-Poveda EA and Barrios P (2013) Perception of stochastically undersampled sound waveforms: a model of auditory deafferentation. Front. Neurosci. 7:124. doi: 10.3389/fnins.2013.00124
Received: 28 March 2013; Accepted: 26 June 2013;
Published online: 16 July 2013.
Edited by:Andrew J. Oxenham, University of Minnesota, USA
Reviewed by:Christophe Micheyl, University of Minnesota, USA
Copyright © 2013 Lopez-Poveda and Barrios. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in other forums, provided the original authors and source are credited and subject to any copyright notices concerning any third-party graphics etc.
*Correspondence: Enrique A. Lopez-Poveda, Instituto de Neurociencias de Castilla y León Universidad de Salamanca, Calle Pintor Fernando Gallego 1, 37007 Salamanca, Spain e-mail: firstname.lastname@example.org