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AW: Cochlear Maps
Dear Donald and List,
Although Fig. 11-39 of von Békésy's book "Experiments in
Hearing" (1960) was drawn long before the discovery of active
amplification in outer hair cells (1985), it implies that, for a
given sine-tone frequency in the range from 100 to 1000 Hz,
the x-coordinate given by the "active" map ("localization from
hearing loss measurements") is greater (i.e., farther from
the stapes) than that of the "passive" map by 4 or 5 mm.
At low and high frequencies, the differences
x(active) - x(passive) appear to be smaller, so that in a plot
of log(f) versus x the shapes of the two curves differ.
At the "active" peak, the cochlear wave is still travelling;
at a given sine-tone frequency of a few kHz, the "resonance"
location is therefore even more apical than the "active" one,
by typically 2 mm in humans.
I have to admit, however, that I do not know whether
von Békésy's data have been contradicted by later ones.
Reinhart Frosch.
Reinhart Frosch,
Dr. phil. nat.,
r. PSI and ETH Zurich,
Sommerhaldenstr. 5B,
CH-5200 Brugg.
Phone: 0041 56 441 77 72.
Mobile: 0041 79 754 30 32.
E-mail: reinifrosch@xxxxxxxxxx .
----Ursprüngliche Nachricht----
Von: ddg@xxxxxxxxxx
Datum: 25.09.2006 19:32
An: <AUDITORY@xxxxxxxxxxxxxxx>
Betreff: Cochlear Maps
Dear Dr. Reinhart Frosch and List,
[...]
In whatever way my 1961,1990 empirical-descriptive curve is now to
be
categorized, the frequency-place data summarized in my 1990 paper
cannot be so neatly divided into (a) data from dead humans and (b)
in
vivo data obtained at only high (> 100 dB SPL) levels in the
various
other species considered.
[...]
Of course, Bekesy's data are from dead cochleas, and were also
obtained
at very high signal levels, so that "passive" or "passive-mode"
data
may be an appropriate way to describe them. Not so for most of the
in
vivo data, mis-characterized above as having been obtained at very
hign
signal levels. Much of the in vivo frequency-place data in other
species summarized in 1990 were not obtained using tones greater
than
100 dB, quite notably not in the case of Liberman's (1982) very
full
set of data (or Kohlloffel's basal data - 1974,75) in the cat,
where
single unit CF determinations (i.e. near-threshold measurements)
were
related to fiber place of origin along the cochlea. In addition,
Muller's Mongolian gerbil data [(1996) in Hear Res, 94, 148-196]
were
obtained in the same way as Liberman's. CFs determined at tuning
curve
tips uniformly measured at signal levels over 100 dB SPL?
In the guinea pig probably the mechanical data (i.e. Wilson and
Johnstone's) were obtained at fairly high signal levels (and from
cochleas in an altered condition), so call them "passive", but not,
I
think, Dallos' data (using CM). Moreover, as for the other GP
data, we
are back to CFs: Russell and Sellick (inner haircell CFs), or
Robertson and Manley (spiral ganglion cell CFs).
Data from the chinchilla (Eldredge, CID data) and data of Stebbins
and
Moody (1979- 88), relating to a species of old-world monkey,
related
place of cochlear lesion to cut-off frequencies (a threshold curve
"shoulder" related to place of loss) and hence were obtained
differently than in the experiments above, but not at particularly
high
levels.
It needs to be recognized by list members not working on cochlear
issues that most of the in vivo data collated in the 1990 paper
cannot
be characterized correctly as obtained only, or even largely, at
very
high signal levels, but rather the reverse. Most actually would
fall
in the "Active-mode" data category.
Does that raise a problem? Curves of identical form appear to
describe
data obtained at much lesser signal intensity levels than 100 dB
SPL.
The curve is still empirical: one parameter (exponential
coefficient)
can remain identical, a second nearly so, with only the third
varying
to accommodate different frequency ranges. But is the curve now
"active", having been "passive" in respect to dead human data (and
the
one "passive" set of GP data)?.
The same curve form would seem oddly categorized if called both
"passive" (when applied to dead humans and Keele guinea pigs) and
"active" (when applied to EPL cats and Sussex and Evanston guinea
pigs), i.e. depending just on the data or conditions applied to.
Perhaps, better apply the terms at this point only to data sets
themselves, depending on stimulus level used or cochlear physical
condition. But, it also seems that some data sets obtained at
high
signal levels in the Keele guinea pigs appeared to agree with
other
data sets obtained at low signal levels in other guinea pigs - an
oddness noted in a 1990 footnote. If that agreement were valid,
what
do the terms "passive" and "active" mean in that context? This is
not
to deny importance to efforts to use such terms and address these
issues; it is only perhaps to illustrate that a theoretician's lot
may
not be a happy one if the data cupboard is opened. Some data may
be
hard to reconcile with others - or with theoretical positions.
I hope this "clarification" of the in vivo data reviewed in 1990
will
be helpful - in trying to redirect attention to the methods used
and
actual conditions under which each type of such data (in the field,
not
just in that paper) have been obtained, however discouraging that
may
be on occasion.
Cheers,
Donald D. Greenwood