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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.
Dr. phil. nat.,
r. PSI and ETH Zurich,
Phone: 0041 56 441 77 72.
Mobile: 0041 79 754 30 32.
E-mail: reinifrosch@xxxxxxxxxx .
Datum: 25.09.2006 19:32
Betreff: Cochlear Maps
Dear Dr. Reinhart Frosch and List,
In whatever way my 1961,1990 empirical-descriptive curve is now to
categorized, the frequency-place data summarized in my 1990 paper
cannot be so neatly divided into (a) data from dead humans and (b)
vivo data obtained at only high (> 100 dB SPL) levels in the
other species considered.
Of course, Bekesy's data are from dead cochleas, and were also
at very high signal levels, so that "passive" or "passive-mode"
may be an appropriate way to describe them. Not so for most of the
vivo data, mis-characterized above as having been obtained at very
signal levels. Much of the in vivo frequency-place data in other
species summarized in 1990 were not obtained using tones greater
100 dB, quite notably not in the case of Liberman's (1982) very
set of data (or Kohlloffel's basal data - 1974,75) in the cat,
single unit CF determinations (i.e. near-threshold measurements)
related to fiber place of origin along the cochlea. In addition,
Muller's Mongolian gerbil data [(1996) in Hear Res, 94, 148-196]
obtained in the same way as Liberman's. CFs determined at tuning
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,
think, Dallos' data (using CM). Moreover, as for the other GP
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
Moody (1979- 88), relating to a species of old-world monkey,
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
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
be characterized correctly as obtained only, or even largely, at
high signal levels, but rather the reverse. Most actually would
in the "Active-mode" data category.
Does that raise a problem? Curves of identical form appear to
data obtained at much lesser signal intensity levels than 100 dB
The curve is still empirical: one parameter (exponential
can remain identical, a second nearly so, with only the third
to accommodate different frequency ranges. But is the curve now
"active", having been "passive" in respect to dead human data (and
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
signal levels in the Keele guinea pigs appeared to agree with
data sets obtained at low signal levels in other guinea pigs - an
oddness noted in a 1990 footnote. If that agreement were valid,
do the terms "passive" and "active" mean in that context? This is
to deny importance to efforts to use such terms and address these
issues; it is only perhaps to illustrate that a theoretician's lot
not be a happy one if the data cupboard is opened. Some data may
hard to reconcile with others - or with theoretical positions.
I hope this "clarification" of the in vivo data reviewed in 1990
be helpful - in trying to redirect attention to the methods used
actual conditions under which each type of such data (in the field,
just in that paper) have been obtained, however discouraging that
be on occasion.
Donald D. Greenwood