Subject: Re: Cochlear Delays From: David Mountain <dcm(at)BU.EDU> Date: Tue, 3 Feb 2004 08:29:55 -0500I 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 Boston University 44 Cummington St. Boston, MA 02215 Email: dcm(at)bu.edu Website: http://earlab.bu.edu/external/dcm/ 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 > andrew.bell(at)anu.edu.au > phone +61 2 6125 9634 > fax +61 2 6125 3808 > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ >