Subject: Cochlear nonlinearity & TTS From: Navid Shahnaz <nshahnaz@xxxxxxxx> Date: Mon, 15 Jan 2007 08:46:33 -0800 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>--------------Boundary-00=_L95X12S0000000000000 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Dear List=0D I've been trying to find a good explanation on why TTS occur about half a= n octave to an octave higher than than the exposure frequency. When you loo= k 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 lo= wer frequencies (apicalward); however, when you look at travelling wave on t= he 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=20 basalward. The latter proposes that the amplifier should be more apical t= o the CF; therefore, damaging this area will result in a shift in threshold toward more basal side. Your clarification is highly appreciated.=0D Best=0D Navid=0D --------------------------------------------------------------------=0D Navid Shahnaz, Ph.D., Aud. (C)=0D Assistant Professor=0D School of Audiology & Speech Sciences=0D Faculty of Medicine=0D University of British Columbia=0D 5804 Fairview Ave., J. Mather Building=0D Vancouver, BC Canada V6T 1Z3=0D Tel. 604- 822-5953=0D Fax.604-822-6569=0D E-mail: nshahnaz@xxxxxxxx=0D Website:http://www.audiospeech.ubc.ca/school/faculty/navid/ --------------Boundary-00=_L95X12S0000000000000 Content-Type: Text/HTML; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable <HTML><HEAD> <META http-equiv=3DContent-Type content=3D"text/html; charset=3Diso-8859-= 1"> <META content=3D"IncrediMail 1.0" name=3DGENERATOR></HEAD> <BODY style=3D"BACKGROUND-POSITION: 0px 0px; FONT-SIZE: 12pt; MARGIN: 5px= 10px 10px; FONT-FAMILY: Arial" bgColor=3D#ffffff background=3D"" scroll=3D= yes ORGYPOS=3D"0"> <TABLE id=3DINCREDIMAINTABLE cellSpacing=3D0 cellPadding=3D2 width=3D"100= %" border=3D0> <TBODY> <TR> <TD id=3DINCREDITEXTREGION style=3D"FONT-SIZE: 12pt; CURSOR: auto; FONT-F= AMILY: Arial" width=3D"100%"> <DIV>Dear List</DIV> <DIV>I've been trying to find a good explanation on why TTS occur about h= alf an octave to an octave higher than than the exposure frequency. When = you look at BM displacement patterns (Johnstone, 1986; Ruggero et a= l., 1997) as a function of frequency for a given center frequen= cy at multiple levels you will notice that first the cochlea will lose it= s nonlinearity at the best frequency at high levels and the best fre= quency shifts more toward the lower frequencies (apicalward); however, wh= en you look at travelling wave on the BM for a given center frequen= cy at multiple levels the best frequency shifts toward higher frequ= encies (basalward) with increasing levels (Ren, 2002). This level depende= nt shift has been proposed as an explanation for a shift in TTS. My quest= ion is why displacement of BM for the CF is more toward the apical s= ide at high levels while the travelling wave is basalward. The latt= er proposes that the amplifier should be more apical to the CF; therefore= , damaging this area will result in a shift in threshold toward more basa= l side. Your clarification is highly appreciated.</DIV> <DIV>Best</DIV> <DIV>Navid</DIV> <DIV> <DIV><FONT face=3DArial size=3D2>----------------------------------------= ----------------------------<BR>Navid Shahnaz, Ph.D., Aud. (C)<BR>Assista= nt Professor<BR>School of Audiology & Speech Sciences<BR>Faculty of M= edicine<BR>University of British Columbia<BR>5804 Fairview Ave., J. Mathe= r Building<BR>Vancouver, BC Canada V6T 1Z3<BR>Tel. 604- 822-5953<BR>Fax.6= 04-822-6569<BR>E-mail: <A title=3Dmailto:nshahnaz@xxxxxxxx href= =3D"mailto:nshahnaz@xxxxxxxx">nshahnaz@xxxxxxxx</A></= FONT></DIV> <DIV>Website:<A href=3D"http://www.audiospeech.ubc.ca/school/faculty/navi= d/">http://www.audiospeech.ubc.ca/school/faculty/navid/</A></DIV></DIV></= TD></TR> <TR> <TD id=3DINCREDIFOOTER width=3D"100%"> <TABLE cellSpacing=3D0 cellPadding=3D0 width=3D"100%"> <TBODY> <TR> <TD width=3D"100%"></TD> <TD id=3DINCREDISOUND vAlign=3Dbottom align=3Dmiddle></TD> <TD id=3DINCREDIANIM vAlign=3Dbottom align=3Dmiddle></TD></TR></TBODY></T= ABLE></TD></TR></TBODY></TABLE></BODY></HTML> --------------Boundary-00=_L95X12S0000000000000--