Effects of sensorineural hearing loss on temporal coding of narrowband and broadband signals in the auditory periphery

Abstract

People with sensorineural hearing loss have substantial difficulty understanding speech under degraded listening conditions. Behavioral studies suggest that this difficulty may be caused by changes in auditory processing of the rapidly-varying temporal fine structure (TFS) of acoustic signals. In this paper, we review the presently known effects of sensorineural hearing loss on processing of TFS and slower envelope modulations in the peripheral auditory system of mammals. Cochlear damage has relatively subtle effects on phase locking by auditory-nerve fibers to the temporal structure of narrowband signals under quiet conditions. In background noise, however, sensorineural loss does substantially reduce phase locking to the TFS of pure-tone stimuli. For auditory processing of broadband stimuli, sensorineural hearing loss has been shown to severely alter the neural representation of temporal information along the tonotopic axis of the cochlea. Notably, auditory-nerve fibers innervating the high-frequency part of the cochlea grow increasingly responsive to low-frequency TFS information and less responsive to temporal information near their characteristic frequency (CF). Cochlear damage also increases the correlation of the response to TFS across fibers of varying CF, decreases the traveling-wave delay between TFS responses of fibers with different CFs, and can increase the range of temporal modulation frequencies encoded in the periphery for broadband sounds. Weaker neural coding of temporal structure in background noise and degraded coding of broadband signals along the tonotopic axis of the cochlea are expected to contribute considerably to speech perception problems in people with sensorineural hearing loss.

Distorted Tonotopic Coding of Temporal Envelope and Fine Structure with Noise-Induced Hearing Loss

“…Note that this downward shift of the upper limit for TFS coding of broadband noise contrasts with the lack of shift typically observed for phase locking to narrowband sounds (e.g., tones) in quiet environments (Harrison and Evans, 1979;Miller et al, 1997;Kale and Heinz, 2010). This contrast highlights the importance of studying the effects of cochlear hearing loss using complex sounds (Henry and Heinz, 2013), for which lower-frequency TFS can overwhelm the less-robust TFS coding near CF (due to the normal roll off in phase locking; Johnson, 1980) in noise-exposed basal fibers with a reduced tip-to-tail ratio in the tuning curve (e.g., from hypersensitive tails).…”

“…Neurophysiological data were recorded from auditory nerve fibers under anesthesia Ն3 weeks after the noise exposure using standard procedures in our laboratory Heinz, 2010, 2012;Henry and Heinz, 2012). Previous research in cats shows that noise-induced threshold shifts are stable beginning 19 d following noise overexposure (Miller et al, 1963).…”

“…Surprisingly, neurophysiological studies in nonhuman animals have shown relatively few changes in temporal processing with cochlear damage (Henry and Heinz, 2013). In auditory nerve fibers, noise overexposure does not affect phase locking to the TFS of tones and amplitude-modulated tones in quiet environments, and in fact enhances ENV coding (Miller et al, 1997;Heinz, 2010, 2012;Henry et al, 2014).…”

“…In auditory nerve fibers, noise overexposure does not affect phase locking to the TFS of tones and amplitude-modulated tones in quiet environments, and in fact enhances ENV coding (Miller et al, 1997;Heinz, 2010, 2012;Henry et al, 2014). In contrast, TFS coding is reduced for tones in noisy environments and altered for synthetic vowels (i.e., reduced synchrony capture; Miller et al, 1997).…”

Effects of Sound-Induced Hearing Loss and Hearing Aids on the Perception of Music

“…IHC damage may lead to a disruption of the temporal synchrony between the waveform on the BM and the action potentials (spikes) in the auditory nerve, although this effect appears to be small in animal models of noise-induced hearing loss [21,22]. IHC, synaptic, and neural damage can all reduce the number of nerve spikes transmitted along the auditory nerve, leading to less precise neural coding of the properties of sounds.…”