Coadaptation does not seem to be the correct term. Coadaptation does not mean “the use of a biological feature evolved for one purpose for a different purpose” which is how Steven Novella defines coaptation.

—————————–

Jeremiah,

The problem with coaptation is that I cannot find it defined as such in any dictionary. It seems to have only one definiton: “The bringing together of two parts to form a seamless whole”.

“I wonder if anyone has tried using an electronic device to generate clicks.”

This is not quite the same thing, but it’s close:

http://news.bbc.co.uk/2/hi/science/nature/3171226.stm

Love the blog and the podcast.

http://www.blackwellpublishing.com/ridley/a-z/Coadaptation.asp

“This is due, in part, to coaptation – the use of a biological feature evolved for one purpose for a different purpose.”

Are you sure that’s what it’s called.
There is preadaptation, exaptation, and cooption, which mean roughly the same thing.
But I have never heard of coaptation in evolution.
Coaptation means lining up and joining two surfaces or edges together.

Ive just got regular old echolocution…it works well enough though.

The rain,rain,rain,in Spain,Spain,Spain,falls mainly,mainly,mainly…

He always said that you could hear 40 kHz, if it was loud enough. His hearing was totally trashed from exposure to high intensity ultrasound.

All the tuning of sensory systems is automatic (and poorly understood). I think assuming that there is a lot about human ecolocation that we don’t understand is the safest default and that systems should be produced that make signals with a fidelity that is beyond what average, or even exceptional individuals need.

“Your neural hardware is tuned to the specific shape of your ear, someone else’s ears cause their neural hardware to tune to their ears. You want your neural hardware to tune to the shape of your ears.

Changing from one set of ears to another is going to degrade the auto-tuning. ”

I agree – in principle. Of course, we don’t really know, but I suspect it won’t make much difference in practice. If you really had a sharp spike for your click, it would have equal power at all frequencies (of interest), and rather than tuning it for a specific ear, the ear (of course, we mean the processing system behind it) will adapt.

The man whose ideas led to the things I’ve described, Dwayne Batteau (no longer with us), thought that to decode a wide range of acoustic phenomena, the brain must have a very powerful and probably generalized capability to perform deconvolutions. He certainly made that seem very plausible to me. If that’s right, I’d think that a particular brain could adapt very well to another pair of ears, or a different form of sonar pulses, etc.

“Changing from one set of ears to another is going to degrade the auto-tuning.” What I’m saying is that, from my limited experience and from talking with others who had more, is that using other ears works surprisingly well. Of course, all this speculation is subject to actually trying it out.

tmac57 said

“Is there any evidence that humans can perceive anything beyond 20kHz?”

The people I worked with who had a lot more experience with this equipment than I did said that it was necessary to reproduce frequencies up to about 40 khz to get the full presence effect. As d2u said, the size of the ear structures fits in with this. As I said, the thinking was not that a person could actually sense *frequencies* that high, but that small phase differences *could* affect the presence of the sound, and to reproduce those, they needed the high frequency response. OTOH, I never made any experiments about this myself.

One thing to remember is that many (but not all) people can localize sound sources in the vertical plane, even though their source is on the midplane. Many can do this even with just one ear in use. Binaural phase differences couldn’t support this ability. If you bend down your pinnae and try again to localize the source, you can’t. This shows that vertical localization depends on the detailed shape of the external ear, which is asymmetrical in the vertical plane. The asymmetry would be necessary to perform vertical localization.

Just to get a really rough numerical view of all this, the speed of sound at sea level is about 1000 ft/sec, or 12,000 inches/sec. For a frequency of 40khz. the wavelength is about 12,000/40,000 = 0.3 inches. So if we want to resolve sizes comparable to structures of the external ear – say around 1/8 – 1/4 inches, 20 khz seems too low and 40 khz would be more plausible. Again, this does not say that a person can actually *hear* tones at 40 khz.