Many people don’t realise that as we get older it is not just our hearing which declines but because of the hearing decline our ability to tell which direction sounds come from, or localisation as it is known, is also affected. This includes localising sounds from the side or front and back. Our ears and brain rely on two main processes to localise side sound sounds. They use a comparison between the volume and time differences between the two ears to do this. A sound coming from one side will seem louder in the ear closer to the sound and softer in the ear further from the sound because our head shadows the sound. Our brain then analyses the volume differences between the ears and gives us an idea on which side the sound is coming from.
At the same time the brain is also analysing the timing difference between the ears for telling where high pitched sounds come from. The sound will reach the ear closer to the sound earlier than the distal ear and the sound wave is consequently altered because of this and the brain recognises the difference in sound wave patterns. The shape and positioning of the ear itself further aids us in localising front and back sounds. The pinnae’s (the pinnae is the outer part of your ear) shape and positioning is designed to accentuate the sounds in front more than the sounds behind. And the folds of skin and cartilage of our ear are designed to trap the high pitched sounds from the front and direct them towards our ear canals.
The problem we have with localisation as we get older is we lose our high pitched hearing. This causes problems with our brains ability to use the timing differences between ears because there are less sounds that the brain can analyse and use. Our front and back localising is also effected as although the folds in the skin are collecting the high pitched sounds from the front and directing it towards the ear canal, the inner itself is not able to hear them and consequently there is little perceivable difference in sounds from the front and back.
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