Localisation - identifying where sound comes from
  • Mar 3, 2020

Localisation - identifying where sound comes from

Have you ever had trouble locating a sound? Maybe your phone in another room?

Your hearing plays a large role in how you detect and locate sounds, called localisation.

Interaural Time Difference ITD

Interaural time difference is the difference in arrival time of a sound between two ears.

It provides clues for direction and angle of the sound source.

This is the difference in timing that it takes for sound to reach one ear and then reach the other ear.

So someone is talking to you from your righ-side the sound will arrive to your right ear quicker and louder than your left ear.
The difference in timing, tells your brain that that sound is coming from that direction.

Interval Level Differences ILDS

This is the difference in intensity of sound between your ears caused by the head shadow effect and distance.

The head shadow effect is a phenomenon that happens when sound has to travel through and around your head before it can be heard by your opposite ear.

It is typically six to seven decibels softer than it was in the ear, that was on the side of the sound source. Thus this effect helps your brain locate the source of the sound.

Musicians learn interval ear training to help differentiate and seperate notes Can those skills be used to differentiate voices in noisy environments like an airport?

Sound Localisation

Two Functioning Ears

Two functioning ears are required to be able to determine where sound is coming from.

 

Ear Anatomy

Pinna Effects

People with normal hearing are really good at identifying where sound is coming from, in the horizontal plane, and they're also really good at identifying where sound is coming from, in the vertical plane.

If you actually have something in your vertical plane that is completely centered with your head, you're not going to have a whole lot of timing, or level differences between both of your ears.

This is where the unique size and shape of your Pinna (the visible part of the ear) comes into play.

The shape of your Pinna is something that helps you identify where in your vertical plane sound is coming from and your brain is attuned to this over your lifespan.

There is an easy way to demonstrate this if you can actually get a friend to jingle a set of car keys, it's somewhere in your vertical plane with your eyes closed, you can usually identify very accurately where that

sound is coming from, but if you actually take your ears and contort them and kind of squish them around and then try to do the same thing, it becomes increasingly difficult to understand where in your vertical plane that sound is coming from.

If you're having issues in identifying where sound is actually coming from then you absolutely have to go in and get your hearing assessed, because that is what is controlling your ability to actually perform localisation.

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