[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: mechanical cochlear model
Dick, and others,
....... You are correct in saying that there is good "evidence for the
view that the basilar membrane traveling wave peaks about half an octave
basalwards of the neural CF", for high enough levels.
Good we agree on that.
Only at very low levels does the wave, or the neural response, peak near
the CF place.
At low levels (below ca 60 dB SPL) a traveling wave (TW) has never been
observed, despite 20 years of laser interferometric measurements of basilar
membrane (BM) motion in vivo down into the subnanometer range. To the
contrary, the labs of Ian Russell in England and Tianying Ren in Oregon have
indpendently and by different methods reported a wealth of data that show a
point excitation of the BM at low levels, without any indication whatsoever
that also a TW might be involved. The main findings are:
1) Pure tones move a very short longitudinal section of the BM, with the
adjacent sections on either end remaining totally unmoved.
2) The excited section extends symmetrical around the place of
characteristic frequency (CF).
These findings are not compatible with a low-level TW. However, they are
compatible with local resonance (e.g. via tuned outer hair cells (OHC))
As an example of evidence that's hard to explain, we have the
blocked-round-window experiment of Perez 2009. It needs to be
investigated further, [.........]
Martin, since I don't have the Perez paper handy, can you tell us what the
statistical support was for their observation that "In the four control
ears, there was no change in ABR threshold 24 hours after the round window
was occluded."? Would a hypothesis of a few dB of threshold rise be
equally compatible with their data? That's what the "third physiological
window" idea would suggest.
No, it would not. The threshold statistics in dB pe SPL (mean & SD) for the
four control ears are:
Initial: 56.3 +/- 2.5
Post-block: 58.8 +/- 4.8
24 h later: 57.5 +/- 5.0
Neuroscience of Music
S-671 95 Klässbol
web site: http://www.neuroscience-of-music.se/index.htm