They will perceive sounds differently, yet the audiogram suggests that they have the same degree of loss. Huss and Moore investigated how hearing impaired patients perceive pure tones, and found that they perceive tones as noisy and distorted, more (on average) than a person without a hearing impairment. However, they also found that the perception of tones as being like noise, was not directly related to frequencies within the dead regions, and was therefore not an indicator of a dead region. This therefore suggests that audiograms, and their poor representation of dead regions, are inaccurate predictors of a patients perception of pure tone quality.Research by Kluk and Moore  has shown that dead regions may also affect the patients perception of frequencies beyond the dead regions. There is an enhancement in the ability to distinguish between tones that differ very slightly in frequency, in regions just beyond the dead regions compared to tones further away. An explanation for this may be that cortical re-mapping has occurred. Whereby, neurons which would normally be stimulated by the dead region, have been reassigned to respond to functioning areas near it. This leads to an over-representation of these areas, resulting in an increased perceptual sensitivity to small frequency differences in tones. Vestibulocochlear nerve pathology
congenital deformity of the internal auditory canal,
neoplastic and pseudo-neoplastic lesions, with special detailed emphasis on schwannoma of the eighth cranial nerve (acoustic neuroma),
non-neoplastic Internal Auditory Canal/CerebelloPontine Angle pathology, including vascular loops,

Diagnosis
Case history
Before examination, a case history provides guidance about the context of the hearing loss.
Some veterinarians and hoof care practitioners recommend exercising the horse on varied terrain to stimulate and strengthen the caudal hoof structures. Medication
Vasodilators improve the blood flow into the vessels of the hoof. Examples include isoxsuprine (currently unavailable in the UK) and pentoxifylline. Anticoagulants can also improve blood flow. The use of warfarin has been proposed, but the extensive monitoring required makes it unsuitable in most cases. Anti-inflammatory drugs are used to treat the pain, and can help the lameness resolve sometimes if shoeing and training changes are made. Include Nonsteroidal anti-inflammatory drugs (NSAIDs), corticosteroids, and other joint medications. The use of intramuscular glycosaminoglycans has been shown to decrease pain in horses with navicular disease, but this effect wanes after discontinuation of therapy. Oral glycosaminoglycans may have a similar effect.Bisphosphonates can be useful in cases where bone remodeling is causing pain.Gallium nitrate (GaN) has been hypothesized as a possible treatment for navicular disease, but its benefits have not been confirmed by formal clinical studies. One pilot study examined horses given gallium nitrate in their feed rations. While it was absorbed slowly, it did stay in the animals system, providing a baseline dosage for future studies. Surgery
Palmar digital neurectomy (or "nerving" or "denerving") is not without adverse side effects and should therefore be used as a last resort. In this procedure, the palmar digital nerves are severed, so the horse loses sensation in the back of the foot.