Subject: Re: Traveling waves or resonance? From: Andrew Bell <andrew.bell(at)anu.edu.au> Date: Mon, 18 Oct 2004 15:51:26 +1000Martin: I think your efforts at clarification actually muddy the waters, as I can't agree with your attempts to dispel two "popular misconceptions". 1. Of course Gold predicted spontaneous otoacoustic emissions as well as the cochlear amplifier. The reason is that the former depend on the latter. As he explained it, positive feedback could easily be excessive and lead to continuous oscillation. Following the logic through, he placed a microphone in an ear canal and tried to detect the oscillation. A wonderful experiment that had to wait until Kemp's efforts a quarter of a century later for success. You criticise Gold's experiment because he caused the ear to ring beforehand by imposing a loud sound, so you say he was really trying to detect tonal tinnitus. Yes, there is a leap in logic in linking tonal tinnitus with spontaneous mechanical activity produced by positive feedback in the cochlea, but the leap is reasonable - both phenomena have similar characteristics (continuous narrow-band oscillation) and relate to the ear. It turns out that usually the frequencies of the two phenomena are different, but there are cases in which the objective SOAE frequencies match the subjective ones (as you allow with your qualifier "vast majority of cases"). I can subjectively hear the 1440 Hz SOAE in my left ear, for example. But then you say tinnitus can "never" be picked up with a microphone, which, in the light of the foregoing, is clearly not the case. Even if you meant that tinnitus originating as neural activity can never drive the cochlea in reverse and be detected with a microphone, that is just a preconceived notion, as we just don't know. It's a leap of logic which is exactly the opposite of Gold's conjecture that tinnitus _always_ has a counterpart in the cochlea and ear canal. I remain open-minded on the possible connection between the subjective (tinnitus) and objective (SOAEs) aspects of the auditory system. It's an exciting one that is best not prejudged. As the saying goes, if it looks like a duck, sounds like a duck, and walks like a duck, then it's very likely that it is a duck. 2. I would not dismiss as "silly" Gold's argument that amplification before detection is a sound strategy in signal detection. It means that signal-to-noise ratio is preserved, and that is a fundamental physical principle which has to be obeyed in order to detect signals down at the theoretical limits. Andrew. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Andrew Bell Research School of Biological Sciences The Australian National University Canberra, ACT 0200, Australia T: +61 2 6125 9634 F: +61 2 6125 3808 andrew.bell(at)anu.edu.au ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -----Original Message----- From: AUDITORY Research in Auditory Perception [mailto:AUDITORY(at)LISTS.MCGILL.CA] On Behalf Of Martin Braun Sent: Monday, 18 October 2004 4:42 AM To: AUDITORY(at)LISTS.MCGILL.CA Subject: Re: [AUDITORY] Traveling waves or resonance? On Friday, October 15, Andrew Bell wrote: > .... Happily, > progress has been made in my endeavours to revive a resonance theory of > hearing Current knowledge on resonance, traveling waves, and amplifiers in the inner ear goes well beyond that what Andrew Bell now reviews. Also, the main parts of this information is easily accessible on the web. I would like to comment, however, on two popular misconceptions, which were now repeated again, and for which no, or very little, information is available on the web. 1) Thomas Gold predicted the cochlear amplifier, but not otoacoustic emissions (OAEs). The "ringing in the ear" which he tried to measure, was tonal tinnitus, which, in the vast majority of cases, has nothing to do with OAEs. Such tinnitus is nearly always neurally based and can never be picked up with any microphone. 2) Gold's argument that the inner ear "needed" a mechanical amplifier before the stage of neural transmission is actually quite silly. Other sensory organs have their amplification cascades on a biochemical level within the sensory cells. The same also works in hearing. Only birds and mammals have specialized mechanical pre-amp cells, as an additional mechanism. This "design" provides several advantages, but it is by no means a precondition of hyper-sensitive hearing. Martin ---------------------------- Martin Braun Neuroscience of Music S-671 95 Klässbol Sweden web site: http://w1.570.telia.com/~u57011259/index.htm