Cochlea Damage The majority of hearing losses in the world are due to damage caused to the cochlea,(sensori-neural). In nearly all cases the patient will struggle with speech discrimination ( "I can hear your voice but you sound like you are muttering")
This is made even worse in the presence of background noise. The fitting of hearing aids will be beneficial, but simply amplifying sounds will not overcome the problems found in the cochlea. We will now look at the various problems within the cochlea.
Loudness Recruitment
People with cochlea damage need a greater level of sound to hear well, but when sounds get louder they become just as intolerant of loud sounds as people with no hearing impairment. As seen in audiometry, this leaves the patient with a reduced dynamic range. This causes problems with speech discrimination, as the dynamic range of speech is about 50dB i.e. a 50dB intensity difference between the loudest and quietest parts of speech.Someone with a reduced dynamic range may not be able to accommodate the whole range of speech, which could become a problem when a hearing aid is fitted.
A hearing instrument with the ability to adjust the amounts of amplification will provide a better option for patients with a reduced dynamic range.Recruitment is found only in patients with cochlea (hair cell) damage. The term "abnormal growth of loudness" is commonly used and relates to patients perception of loudness throughout their dynamic range.
A full explanation of cochlea damage can be found here.
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