Where is Sound Coming From? | How Humans Use Sound LOCALIZATION

By: Dr Cliff Olson
October 14, 2019
Video Transcript

Single Sided Deafness (SSD) Treatment Options:  https://youtu.be/16LC2FYu1-U

At least once a week, I lose my phone somewhere in my house, and I have to ask my wife to call it so I can listen to the vibration.   After about 3 or 4 tries, I can eventually locate my phone.  Obviously, your hearing plays a role in identifying where sound is coming from, and that process requires two ears.  This process is called Localization. Localization utilizes Interaural Timing Differences, Interaural Level Differences, & Pinna Effects.  

First, let's talk about Interaural Timing Differences or ITDs.  This is the timing difference that it takes for sound to reach one ear vs the other ear.  So, if you have a friend call out your name from your right side, your right ear will hear their voice first, followed by your left ear.  This timing difference indicates to your brain that sound is coming from your right.

Second, let's talk about Interaural Level Differences or ILDs.  This is the volume difference between both of your ears cause by distance and the Head Shadow Effect.  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.  By the time the sound reaches the opposite ear it is typically 6-7 dB SPL softer than it was in the ear that was on the side of the sound source.  Much like Interaural Timing Differences, this indicates to your brain that sound is coming from the louder side.

This is why it is so critical to have two functioning ears to perform Localization of sound.  So, if you have Single Sided Deafness or SSD, you will not have the ability to localize.  This is true even if you treat your hearing loss with CROS or BiCROS.  However, you may be able to achieve some localization with the use of a Cochlear Implant or AmpCROS.

Third, let's talk about Pinna Effects.  The Pinna Effect allows you to better locate sound in the vertical plane.  This can easily be demonstrated by having someone jingle a set of keys with your eyes closed.  Typically, you will be able to identify the location pretty easily.  However, if you contort the shape of your Pinna it can alter how the sound enters your ear and make it more difficult to identify where that sound is in your vertical plane.

There you go, now you know how we use Timing Differences, Level Differences, and Pinna Effects to Localize where sound is coming from.  If you do have issues with our ability to Localize where sound is coming from, I highly recommend you have your hearing evaluated to determine if you have a hearing loss causing the issue.

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