From Trends in Hearing
This review focuses on cochlear neuropathy due to noise exposure and aging as a potential mechanism for this type of loss. Initially it describes some of the early studies investigating hearing disability in the presence of a normal audiogram. Then discussed the results of animal experiments showing that noise exposure can cause substantial cochlear neuropathy without affecting sensitivity to weak sounds. This type of selective neural loss, which has been described recently as hidden hearing loss, may be the physiological basis for many of the cases of hearing disability with a normal audiogram. This is supported by evidence from human studies that noise exposure may cause perceptual difficulties without affecting the audiogram. The review also considers the relation between hidden hearing loss and tinnitus, and the relation between aging and hidden loss.
Dramatic results from recent animal experiments show that noise exposure can cause a selective loss of high-threshold auditory nerve fibers without affecting absolute sensitivity permanently. This cochlear neuropathy has been described as hidden hearing loss, as it is not thought to be detectable using standard measures of audiometric threshold. It is possible that hidden hearing loss is a common condition in humans and may underlie some of the perceptual deficits experienced by people with clinically normal hearing. There is some evidence that a history of noise exposure is associated with difficulties in speech discrimination and temporal processing, even in the absence of any audiometric loss. There is also evidence that the tinnitus experienced by listeners with clinically normal hearing is associated with cochlear neuropathy, as measured using Wave I of the auditory brainstem response. To date, however, there has been no direct link made between noise exposure, cochlear neuropathy, and perceptual difficulties. Animal experiments also reveal that the aging process itself, in the absence of significant noise exposure, is associated with loss of auditory nerve fibers. Evidence from human temporal bone studies and auditory brainstem response measures suggests that this form of hidden loss is common in humans and may have perceptual consequences, in particular, regarding the coding of the temporal aspects of sounds. Hidden hearing loss is potentially a major health issue, and investigations are ongoing to identify the causes and consequences of this troubling condition.
Christopher J. Plack,Daphne Barker, and Garreth Prendergast
Perceptual Consequences of “Hidden” Hearing Loss Trends in Hearing January – December 2014 18: 2331216514550621, first published on September 9, 2014 doi:10.1177/2331216514550621