ARO highlights (at)

Subject: ARO highlights
From:    at <LyonAPPLE.COM>
Date:    Fri, 11 Feb 1994 15:21:34 PST

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. Dick Lyon my ARO highlights: papers 162-169: 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 otoacoustic emissions. 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 revcor-like technique. 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.

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Electrical Engineering Dept., Columbia University