Loudness Hyperacusis: Mechanisms of Loudness Perception and Their Breakdown

This paper is concerned with loudness hyperacusis, a condition where sounds of medium and high levels appear to be louder than normal. The “normal” perception of loudness can be understood using a model that takes into account the processing of sounds in the peripheral auditory system, including the outer ear, middle ear, and cochlea. This model has been modified to take into account the perception of loudness by people with cochlear hearing loss. The model predicts the loudness recruitment typically associated with cochlear hearing loss, and also predicts that hearing loss can sometimes be associated with “over-recruitment,” so that some sounds appear louder than normal. However, the model does not account for the fact that loudness hyperacusis can occur for people with normal or near-normal audiograms. This suggests that factors associated with higher levels in the auditory system also need to be taken into account. Here, two such factors are considered: the functioning of the efferent system regulating the active mechanism in the cochlea, and effects of central plasticity and adaptation. Both may play a role in hyperacusis.