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Re: Cochlear Delays
I would be extremely cautious when it comes to using OAE data to estimate
cochlear group delays. Both experiments and models suggest that OAEs are
not generated in a single place but are instead arise from a distributed
response with the result being a sum of components with different group
delays which can result in both summation and cancelation. Goodman et al.
discuss some of the problems associated with OAEs in their paper and
attempt to get around them by focusing on low sound levels, "good"
waveforms, and extrapolation. The problem with extrapolating the data to
lower sound levels is that it is unlikely that the group delay-SPL curve
is linear at low SPL. If the author's assumptions are correct, one would
expect that the curve would level off at low SPL as do the data from
direct BM measurements (see Fig. 7 in their paper). Unfortunately, their
data are not good enough to establish whether there is a low SPL
assymptote in the OAE group delay.
David C. Mountain, Ph.D.
Professor of Biomedical Engineering
44 Cummington St.
Boston, MA 02215
Phone: (617) 353-4343
FAX: (617) 353-6766
Office: ERB 413
On Tue, 3 Feb 2004, Andrew Bell wrote:
> A recent discussion of delays, with ample references to the literature, can
> be found in the Introduction of the paper by Goodman et al, Hearing Research
> 188 (2004), 57-69 ["Cochlear delays measured with amplitude-modulated
> tone-burst-evoked OAEs"].
> > Dear List:
> > Can any one please summarize and/or give references to the group delays
> > encountered by signals while they are processed by
> > cochlear filters, and propagation delays encountered by signals at
> > various locations along the basilar membrane ?
> > Thanks. Ramdas Kumaresan
> Andrew Bell
> Research School of Biological Sciences
> Institute of Advanced Studies
> Australian National University
> Canberra, ACT 0200, Australia
> phone +61 2 6125 9634
> fax +61 2 6125 3808