How do we know where sounds are coming from? © Getty Images

How do we know where sounds are coming from?

We have only two ears, so why are we so good at pinpointing exactly where a sound has come from?

Asked by: Linda Smith, St Albans

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Your brain is able to do this by comparing tiny differences in the way that sounds affect each ear. A noise coming from the right is slightly louder in your right ear, and reaches it fractionally earlier than your left. A sound in front or behind affects each ear the same way, with intermediate effects in-between. The brain uses these differences, even as small as a 100,000th of a second, to calculate where the sound is coming from. Signals from the ear travel along the auditory nerve to the brainstem, where each individual cell responds to a specific time difference and direction.

Until recently it was assumed that a delay was imposed somewhere between the ears and the brainstem, but it has now been discovered that all of the calculations are done in the brainstem cells, which then signal the result to other parts of the brain – enabling you to hear the sound and 
know, without thinking, just where it’s coming from.


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