Clever ears!!

[matt_london]

<PRE>How do we tell the difference between sounds that come from infront or behind us. Surely with only two ears, one on each side of our head we should only be able to say that the sound is either coming from the left or the right? </PRE>

[Loosehead]

The theory I heard in Biology said that the brain calculates the difference in arrival time at each of the 2 ears, this gives an angle and thus 2 possibilties at said angle in front or at said angle behind, you always check front first.If the arival time is the same then the sound is directly in front or directly behind.

[rja211077]

riiiight....but that hardly answers the question, does it?...so we've worked out that the sound is either coming from directly in front or directly behind, so how do we know which?

[CT]

If you can't see the sound making object, logic dictates the next most likely place it's coming from is behind you, then finally from above. The last is the least likely.

[Loosehead]

well you obviously know it all so bloody well work it out fore yourself. Do I have to spell it out for you?

[Loosehead]

sorry that's directed at rja211077 rather than you matt_london

[Buenchico]

It would be harder to tell 'back' from 'front' if we didn't have outer ears. Sounds from in front of us have an uninterrupted path to the front of the ear canal, whereas those from behind are masked by the outer ear. This leads to a 'muffling' effect of sounds coming from behind us, which the brain uses to help determine the direction of the sound.

Even if someone had their outer ears cut off, however, they would probably still be able to differentiate between sounds coming from the front and the rear. This is because not all sound is transmitted to the inner ear via the ear canal. Some of the vibrations pass through the bones of the skull (especially the jaw bone). Different paths lead to different frequencies being filtered en route to the inner ear. Once again, the brain uses this information to assign a direction to the sound.

Chris

[Space]

Buenchico's theory is interesting , but then how do you differenciate a muffled sound coming from the front from an unmuffled sound coming from behind?

As far as I know, the only way to determine whether a sound is in front or behind... is to slightly turn your head.
Have you noticed how animals do? they rotate their ears around... We humans have to rotate the whole head instead...

[Bob A Job]

I can wiggle my ears, when i tense the muscle behind them the lift slightly and i can hear slightly better behind me (i think because this opens up my ear canal more) i find myself doing this whenever i here a noise, i can also wiggle my left ear on its own.

I have noticed in the past that my hearing is much better than other peoples, and i can determine where a sound comes from quicker than other people. My wife says i get this ability from spending to much time with our cats!

[peagreen]

this is a concept known as the localisation of sound, basically there are two mechanisms that are known to be used but there are tens of hundreds of other theories...

1) monaural cues - filtering. it depends upon the filtering effects of structures like the pinna (outer ear), head shoulders etc.. the sounds are filtered depending on the angle they strike the external structures.. the pinna is the primary structure used iin this..which is why some animals can turn their outer ears and have big ears..

2) Binaural localisation - the comparison of input from two detectors (ie. two ears) the primary binaural cue is the split-second delay between when sound from a source reaches the near ear and the far ear.

i nicked that from my ENT textbook so i hope it helps?