[From Gary Cziko 931115.2305 GMT]
Bill Powers (931115.1130 MST) said to Bruce Nevin (931115.0825):
Thanks for the info about the formants; I noticed that, too. As
to what happens when the voice fundamental is above the formants,
this is truly a puzzle if we believe that the formants contain
the raw material of the perceptions. On the other hand, I have
never found sopranos to be particularly intelligible. You can
understand them if you know what the words are supposed to be,
but then the perception is mostly imagination.
It would be interesting to take a digital recording of speech of a very
high voice and digitally adjust the frequency to make it a low voice. I
wonder what it would sound like when we expect to hear the overtones
sitting in the formants (because the voice is low) but don't (because they
weren't there to begin with in the high voice and changing the pitch won't
put them back).
The vestibulo-optical reflex is truly open loop. If you fixate on
a letter on the screen and turn your head from side to side,
you'll see some apparent motion in the visual field even though
your eye doesn't lose its fixation. This, I think, is evidence of
incorrect position-disturbing signals coming from the VOR and
being interpreted as visual movements.
The apparent motion I detect when doing this on my computer screen appears
to arise from the change of perspective of depth caused by moving my eyes
left and right. I don't see the same effect when I view something on a
large flat wall.
The VOR seems remarkably precise to me. I can still read no matter how
fast I nod my head back and forth, even faster than two cycles a second.
In contrast, I cannot read if what I'm reading is moving only half this
fast. So I would venture to guess that the open-loop VOR is more precise
than the closed-loop visual pursuit system in these circumstances.
Disturbances HAVE been applied to the eyes. The method is
gruesome. You put a large contact lens on the eye with a stalk on
it (sometimes applying a vacuum), and pull on the stalk with a
thread. In the light, the reported subjective experience is
unsettling. The visual scene, to which your eyes remain locked,
seems to swivel around your head opposite to the direction of
pull, at times to the point where it feels as if your eyes are
looking straight behind you, through your head! I don't recall
what the experience is in the dark, but I seem to remember that
there is weak resistance, about what could be accounted for by
the passive stretching of muscles and sclera. There is still
uncertainty, as far as I know, about the existence of stretch
receptors in the eye muscles. The reports I've seen have been
ambiguous.
But were any of these disturbances applied while moving the head and seeing
the VOR was disturbed less than expected? Since the VOR moves the eyes to
compensate for head movement, it can only be tested for resistance to
disturbances while the head is moving, not while it is still.
I'd like to see the equivalent of my throwing demo when disturbances are
applied to the arm after the throwing motion is underway and they are
resisted.--Gary
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Gary A. Cziko Telephone: 217-333-8527
Educational Psychology FAX: 217-244-7620
University of Illinois E-mail: g-cziko@uiuc.edu
1310 S. Sixth Street Radio: N9MJZ
210 Education Building
Champaign, Illinois 61820-6990
USA
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