Subject: Re: Cochlear nonlinearity & TTS From: Monita Chatterjee <mchatterjee@xxxxxxxx> Date: Mon, 15 Jan 2007 12:08:43 -0500 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>Navid: The two are just flip sides of the same coin. At a particular place, the peak of the frequency response shifts to lower frequencies as you increase intensity. This means, for instance, that the place that is tuned to, say, 2000 Hz at low intensities will respond most to, say, 1500 Hz at a somewhat higher intensity. Thus, basal locations respond more and more to lower frequency tones as the intensity increases. If you think in terms of the excitation pattern on the basilar membrane or the traveling wave, you'll see that this means that, for a fixed frequency input (say, 1500 Hz), the peak of the excitation pattern shifts basalward as intensity increases. Hope this helps.. Monita M Chatterjee, Ph.D. Asst Professor, Hearing and Speech Sciences 0100 LeFrak Hall University of Maryland, College Park College Park, MD 20742 (301) 405 7716 >>> Navid Shahnaz <nshahnaz@xxxxxxxx> 01/15/07 11:46 AM >>> Dear List I've been trying to find a good explanation on why TTS occur about half an octave to an octave higher than than the exposure frequency. When you look at BM displacement patterns (Johnstone, 1986; Ruggero et al., 1997) as a function of frequency for a given center frequency at multiple levels you will notice that first the cochlea will lose its nonlinearity at the best frequency at high levels and the best frequency shifts more toward the lower frequencies (apicalward); however, when you look at travelling wave on the BM for a given center frequency at multiple levels the best frequency shifts toward higher frequencies (basalward) with increasing levels (Ren, 2002). This level dependent shift has been proposed as an explanation for a shift in TTS. My question is why displacement of BM for the CF is more toward the apical side at high levels while the travelling wave is basalward. The latter proposes that the amplifier should be more apical to the CF; therefore, damaging this area will result in a shift in threshold toward more basal side. Your clarification is highly appreciated. Best Navid -------------------------------------------------------------------- Navid Shahnaz, Ph.D., Aud. (C) Assistant Professor School of Audiology & Speech Sciences Faculty of Medicine University of British Columbia 5804 Fairview Ave., J. Mather Building Vancouver, BC Canada V6T 1Z3 Tel. 604- 822-5953 Fax.604-822-6569 E-mail: nshahnaz@xxxxxxxx Website:http://www.audiospeech.ubc.ca/school/faculty/navid/