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The recent Midwinter Research Meeting of the Association for Research
in Otolaryngology (ARO) was as usual a great meeting with lots of
good people and results.
And as usual, the information overload was overwhelming. It would
probably do us all good to hear from people who attended what they
thought the highlights were. So, I invite any of you who were
there to share what you found interesting and exciting. I'll start
with a few items I liked.
my ARO highlights:
Except for having to start at 8:00 AM EST, the session organized by Julius
Goldstein on "Cochlear Mechanics: Transition or Revolution?" was great.
Rhode, Ruggero, Guinan, Manley, Dallos, Tubis, Hubbard, and Goldstein
presented their views of where things had been and were going, and then
Neely led a panel of 12 more experts who tried to comment on and summarize
what they had heard about; it got extended to an evening session, too,
which included the "minority view" by Jont Allen that the cochlea is not
active. This session alone is too much to summarize, for me at least.
There was a good chuckle at Rhode's statement that his finding of cochlear
nonlinearity in 1971 "was not widely embraced at the time." I liked the
quantitative data from Dallos which implied that outer hair cells change
their length by an amount roughly equal to 1% of the amount that their
cilia are displaced (at 1200 Hz); it's an open issue whether this is
enough to account for the supposed "cochlear amplifier" gain. Hubbard
made an interesting proposal for a "Consortium for Cochlear Modeling" or
something like that, which would use computer networks to share data,
models, and results for evaluating cochlea models. Geisler was excited
about Steele's recent work on modeling the effect of the longitudinal
tilt of OHC's, which seems to offer a way around time-delays needed in
other models and also a way around some of Jont Allen's evidence re low
round-trip gain. Tubis gave a clear description of how SOAE's resemble
the output of nonlinear oscillators, and showed how that provides strong
evidence for the active cochlea hypothesis. Another big remaining area
of questions is differences between basal and apical regions. And more...
poster 356 "Basilar membrane movement evoked by sound is altered by
electrical stimulatin of the COCB," by Dolan and Nuttall, is I think the
first time the statement in the title has been shown, though it has been
widely hypothesized. In effect, efferent activity reduces mechanical
gain, by amounts up to 22 dB near CF and at low levels. Gain reduction
onset time was around 100-200 msec, and recovery around 600 msec.
Of course the reason I like this is that it's consistent with my
efferent-mediated mechanical AGC models.
poster 376 "The effect of contralateral stimulation on the Q of the
cochlear resonator," by Henson et al, shows a similar gain reduction
caused by sound presented in the other ear, if I may interpret it that
way. They used cochlear microphonic (CM) measurement, not direct
mechanical measurement, to infer how long the BM was resonating in a
high-Q bat cochlea, and showed Q reducing from 350 down to 200 with
noise presented contralaterally. Since Q is proportional to gain in
these systems (we think, except for Jont), that means there's enough
cross coupling to get about 5 dB gain reduction in one ear due to
sound in the other--so the AGC is cross-coupled via the medial
efferents. Previously the evidence for this was even more tenuous,
based only on the fact the contralateral sound could suppress
poster 383 "Encoding of complex sounds in the mesencephalon of a
sonic fish," by Crawford, showed that fish have pitch-tuned (as opposed
to frequency-tuned) neurons with reasonable selectivity in the range
of their communication sounds.
posters 388 and 396 (Temchin et al and Cai&Geisler) and paper 295
(Cheatham&Dallos) looked at aspects of how low-frequency suppressor
tones influence hair-cell and neuron responses during the slow cycle,
with varying results. The problem is that at high enough levels,
suppression sometimes (or always?) occurs in both phases (toward SV
and toward ST), while at low levels it only occurs on one side, but
it's not yet clear what the conditions are. Ruggero (a Temchin
co-author) says it's universal in Chinchilla, but Geisler seldom
sees it in cat, but maybe he didn't go to high enough levels. I was
lucky to be in on their discussion of the difference between their
poster results; maybe next year they'll get convergence. Cheatham
found that the SV phase which would suppress at CF could actually
enhance below CF (if I recall correctly). Anyway, all this is
useful in trying to understand IHC and OHC nonlinearities, but we've
got a way to go yet.
paper 490 "Phase and gain of auditory filters of non-phaselocking fibers
determined by Wiener kernel analysis," by van Dijk et al, I didn't
manage to catch, but I caught Ruggero's reaction. He thought this
technique looked great and would allow us to get lots more good insight
for all those high-CF fibers that don't phase-lock. As I read it, the
timing, phase, and everything can be recovered from the "envelope"
fine structure in response to a known white noise, using a higher-order
paper 600 "Two-tone suppression in basilar membrane mechanics and in
auditory nerve responses are consistent," by Yates and Robertson, showed
how to interpret two-tone rate-level curves from low-spont through
high-spont fibers in a way that made them look consistent, in that there
is a consistent "gain reduction" or shift of threshold toward higher
input levels, in response to a suppressor, just as seen in BM mechnanics.
I had to run to the airport after this, so I didn't get a chance to ask
the author how he interprets the rather high slopes (2 dB/dB) of threshold
shift versus suppressor level. Seems to me that in mechanics that slope
has got to be always less than 1. Maybe he's on the mailing list and
will clue us in...
There was tons more of great stuff. All of you who I misrepresented or
left out, please send us your own highlights of ARO.