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Normal hearing
UNDERSTANDING THE PROCESS

To fully understand the reasons for your hearing loss or hearing impairment, it is important first to understand the process of normal hearing.
Normal hearing occurs when sound enters the external ear, travels through the ear canal and reaches the eardrum.
The eardrum will vibrate with the sound and causes vibration in the chain of the three bones in the middle ear.
The middle ear amplifies the sound waves prior to passing them to the fibres of the inner ear cells.
The vibration is transferred to the inner ear or cochlea, whose nerve fibre endings (specialised receptors, called hair cells) receive the stimulation of sound. Hair cells receive different pitches of sound in accordance with their position. This pattern is maintained all the way into the main auditory area of the brain, to be interpreted as the different pitches that you hear.

The signal is transferred via the auditory nerve to several stations along the way to the brain. One of these, a nucleus in the brainstem receives an equal signal from both ears, and can therefore:

  1. detect sound direction
  2. boost speech above background noise
  3. improve perceptions of balance or symmetry
Then, it is transferred to the auditory cortex in the thinking brain, where the message is understood.
The interpretation of sound is dependent on what you have learnt. Your brain matches the signal to the memory association of it to identify it. When it finds a match, the sound is identified.
Deterioration of memory of sound occurs when we don’t hear normally for a long time. Early action to correct hearing loss restores the normal signal to the brain, maintaining sound memory and sound recognition.

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What do normal hearing test
RESULTS LOOK LIKE?

We measure hearing in decibels which is a measure of sound energy (the loudness or intensity of the sound). Each pitch (or frequency, measured in hertz) across the speech range is measured to find the minimum amount of sound that is required to respond. A graph (audiogram) for each ear can be plotted.

Normal hearing will be found between 0-10 decibels at all pitches.

The World Health Organisation (2020) defines hearing impairment as define hearing loss as a pure tone threshold average (.5; 1; 2; and 4kHz) worse than 25dB in both ears; and disabling hearing loss, poorer than 40dB in adults and 30dB in children in the better ear.

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Mild hearing loss: A person can only hear a sound when it reaches at least 25 to 40dBHL

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Moderate hearing loss: A person can only hear a sound when it reaches 40 to 60 decibels

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Severe hearing loss: A person can only hear a sound when it reaches 60 to 80dBHL

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Profound loss: patients can only hear a sound of 80 dB or more

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Sound understanding can be affecting by parts of the auditory pathway that are not related to the quantity of hearing loss. A proper diagnosis with an audiologist is essential when you suspect a problem with your hearing or understanding of sound.

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