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In Reply to: Re: Very good questions, only 9 is a bit stupid... posted by Kal Rubinson on December 29, 2003 at 18:27:41:
I respond to a few below.1)about how many "hair" per freq. group?
At least two.
[Depends on your definition of group. There is 1 inner and 3 outer hair cells (not hairs) per cross-section but their longitudinal spacing along the basilar membrane is fairly continuous so any grouping is not apparent.]
> > For each ear ;-)3)why do the high freq. "hair" go out 1st with time?
The one's in that range are thin and brittle and susceptable to wear and tare.
[There are several mechanisms but the 'hairs,' themselves, are of similar construction which should make them all equally susceptible. The HF ones are shorter and, thus, stiffer for the higher frequencies such that they can respond better to HF. One possible mechanism is environmental and related to the noises to which one is exposed. Another has to do with the placement of the HF cells at the base of the cochlea where the energy enters.]> > Bend a paperclip 1 time and the wire is still in one piece. Bend it ten times in one place and it breaks. (If you're lucky you reach ten times). It seems there is a mechanical releation. The HF hairs have to bend more often.
If you look at the ears sensitivity level curves you see a fairly flat response at the +95dB level.
Now I wonder about that. Our ancestors didn't have pa systems, lawnmowers or similar devices that generated continous high noise levels for long durations.
(It seems we live longer these days than nature intended.)
[Mebbe. Or mebbe we live under conditions that make it seem so.]4)whats their bandpass characteristics?
Wide band. Neighboring frequencies also cause the hair to resonate. I don't know if you have ever seen the mechanical indicators used to indicate a generators output frequency, they work in a similar fashion. This bell shaped response curve is also observed in certain measurements to determine noise and distortion
[Resonance properties of the hairs and the local mechanical properties of the basilar membrane are both contributors.]> > Yes it's more complicated.
6)how do they couple to the neurons?
Pull out a noisehair and you'll know how.
[Explains nothing. The 'hairs' are extensions, called kinocilia and stereocilia, of the sensory cells. Deflecting them, as when there is relative movement between the basilar and tectorial membranes, opens channels and causes a change in the voltage across the cells membrane. This change modulates the release of a chemical transmitter which is detected by the neurons that transmit the signals to the brain.]
> > So we don't hear the continous sine wave. We sense that hair number 321 is vibrating so there must be a 1 kHz frequency in the spectral content of the varying pressure wave.7)do they exhibit extended decay/ringing to waves?
Yes, but I'll doubt it matters. Inner ear is filled with fluid to transmit the signal more efficient. It also act as dampening.
[True and there are also active tuning/damping mechanisms, some involving those outer hair cells.]> > You can observe this with a simple experiment.
Just listen to music through a walkman on a comfortable level while standing close to a realroad track (Not too close of coarse...)
When a train passes you het the impression that someone is lowering the volume level of the discman. And when the train is just passed you will observe that it takes some little time to 'restore the volume level' to the one you experienced before the train came buy.This shows that the sensivity level is actively adjusted in the hearing mechanism to cope with different loudness levels.
9) why dont i know nothing about this and yet spend 1000s on gear and music?
Different hardwiring in the brain perhaps?
[I appreciate my wife without fundamental understanding......]
> > Yep were all pretty much in the dark on that one...
If they only where willing to tell how the figured out our hard wiring...
Frank
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- Everyday you learn something new. - Frank. 12/30/0300:30:33 12/30/03 (0)
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