Are ears the wiggly ridged shape they are just through pure evolutionary chance - i.e. they aren’t detrimental, so that’s the way they remain - or is there actual useful improvement in hearing due to it?
It seems to me that the concave funnel-like nature of ears would be the real fundamental value to hearing, and not the funny looking channels and ridges on the outer ear lobe itself.
Somewhere I heard that it helps you gauge distance, of all things, due to some very sophisticated signal processing going on in the brain which takes advantage of the fact that the sound has traveled via multiple paths, the lengths of which have different effects on different frequencies. Hopefully someone with more of a clue will come in and 1) confirm that I didn’t make this up, and 2) explain it in some simple terms, because it sounds pretty fascinating.
Look up “kunstkopf” (but you might want to search for English pages only - most of the first page are German). “Kunstkopf” translates as “dummy head” or something similar. The head isn’t very important, but they use casts of real ears to make it work.
The convolutions in our ears give us not only left-right stereo, but info on the vertical angle of a sound, so we hear in 3D. It’s very precise too. I recall studies on sound location, and IIRC the subjects were able to point within 10 degrees or so of the right location, both horizontally and vertically.
On preview I see that galt posted first, and is right that the sound’s distortion by the convolutions that gives the 3D effect.
I can’t help but think that it must be the brain that “tunes” to the ear.
There are so many different shapes for ears it doesn’t seem likely that the ear’s shape is as important as the brain’s ability to map that shape.
That kind of makes sense. Well, in as much as I don’t understand the physics, but I accept that ears may do something this clever so naturally.
I think you might find that while ears have their differences, the internal layout conforms to a basic pattern. Also, it may be that while the ridges etc are different every time the important thing is that there are ridges to create differences that the brain can learn to interpret.
Bear in mind that part of the function of the external ear is not only to collect and focus sound but also to act as a heat exchanger as well. Some of the features may be more conducive to that purpose than the nominal function of hearing.
Stranger
Does anyone know of a study in which people, using normal ears, are compared to those whose ear structures are temporarily changed for the study (by attaching clay, for example)? Did those result in people not being able to locate the sources of sounds as well?
From How Stuff Works.
Have a look around the internet at some images of bats ears. Some are insanely complex with folds and “tubes”, and little ravines.
As many people have mentioned, the shape of the outer ear (pinna) helps us to localize where a sound source comes from. Your two ears can partially determine a sound’s direction from differences between the two ears in the a) time of arrival, and b) amplitude, of a sound. But, that data is not enough information to completely localize sound in 3 dimensions. Also, some of those cues don’t work very well depending on the frequency of the sound (and whether the wavelengths are bigger or smaller than the dimension of your head).
But, the way the sounds bounce off of your torso, head and pinna make the actual signals that arrive at each ear different (not just the intensity and the time). Each ear is receiving a filtered version of the sound, where the actual filter is determined by the direction of the sound source. Yes, you actually can measure this in people by placing small microphones down near the eardrum and observing the differences in what is recorded in each ear. There are differences in each individual (as you might expect), but there are some standard models that seem to match most people with reasonable accuracy.
Your auditory system definately uses this information to localize sounds. In fact, you can apply these different filters to each channel of audio being played over headphones (along with time and amplitude differences) and make it sound like the source is coming from a point in 3-D space. One of the classic papers about this is Kulkarni and Colburn, "Role of spectral detail in sound-source localization ", Nature 396, 747 - 749, December 1998.
If you want more information, these filters go by the name “Head related transfer functions” or commonly just by HRTF. Hit google with either of those terms and you will find a ton of material.
So my recollection was only partially right: the effect of the ear’s shape on the frequency spectrum is used, but for determining direction, not distance.
There’s an example of a “kunstkopf” recording on this page. If you listen to it with headphones, there is definitely a feeling of the various sounds in the room being seperated spatially. However, I get the impression that everything is happening behind me. Is it supposed to sound that way?
slight hijack on shape of ears.
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Galt did you have the headphones on the wrong way round? Just a thought.
No, I tried it both ways. I wouldn’t expect swapping the L and R to change the front-to-back imaging anyway.