Sitting under the piano

[Sarah Fox]

Hi all,

> > Yes, the brain does try to close down the ear canal when sound gets
> > to a certain level.  The sound pressure level that triggers this can
> > be measured by an audiologist.  The muscle that does this is the
> > stapedial muscle.

Yes, the stapedius reflex attenuates sound by about 20 dB, hardly enough to
really matter when one is subjected to continual intense sound.
Furthermore, the stapedius reflex is too slow to be of any use when we
experience sudden bursts of sound (e.g. a drum beat, a crash, etc.).  The
stapedius reflex is really designed to protect us from the noises we are
likely to encounter as a result of our own movements, and it is activated
before any sound is produced.  A classic example is a sneeze.

As has been pointed out, continual sound results in fatigue of the hair
cells in the cochlea.  It ordinarily doesn't result in damage, but here's a
cautionary note for all of you:  Subjecting a person to a continuous tone at
*moderate* sound pressure levels for a long period of time (e.g. a couple of
hours, as I recall) results in a slight but measurable -- and *permanent* --
"notch" in that person's sensitivity curve ("audiogram") at that frequency.
The scientist who discovered this was trying to measure fatigue effects and
did not dream (nor did any of us) that the effects would be permanent.  He
is not likely to publish the results.

There is a related phenomenon in the brain injury arena.  When a neuronal
pathway is overexcited or overstimulated, the neurons are damaged from
"excitotoxicity."  Namely, too much calcium enters the neurons at their axon
terminals, and the free calcium initiates a very destructive chain of events
that can cause the cell to self-destruct.  Many believe (and I agree) that
this is the primary mode of neuronal destruction following mild or moderate
closed head injury, coupled with the circulatory problems that result from
tissue swelling (edema).  Anyway, this *could* be some of what happens to
your auditory pathways when overstimulated.

I notice when I am tuning a piano (... and you can take this with a grain of
salt, considering my "extensive" experience in piano tuning <g>) that if I
work too long with one note I am likely to "fatigue" on that note and become
unable to discern its pitch accurately.  When this happens, I am very
conscious of the implications of neuronal fatigue, and I immediately move on
to other notes to give the hair cells tuned to that note a short rest.  Of
course I also look back over the long hours I spent calibrating sound
systems at a couple dozen frequencies and at levels around 90 - 110 dB SPL.
Hmmmmm....

Peace,
Sarah