Subject: AW: Cochlear nonlinearity & TTS From: "reinifrosch@xxxxxxxx" <reinifrosch@xxxxxxxx> Date: Tue, 16 Jan 2007 12:48:41 +0000 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>------=_Part_20868_11014811.1168951721542 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Dear Navid and List, =20 Two-tone suppression is explained, e.g., in Figure 1.21 of "An Introduction= to the Psychology of Hearing" by B.C.J. Moore (Academic Press, 5th edition= , 2003). Abscissa: frequency (of sine-tones). Ordinate: sound pressure leve= ls.=20 =20 Open circles: tuning curve (threshold versus frequency) of a single neuron = with characteristic frequency of 8 kilohertz. Lowest point of tuning curve:= 8 kilohertz, 10 decibel. =20 An open triangle indicates the first tone: sine-tone of 8 kilohertz, 27 dec= ibel. =20 Black circles: sound pressure level of a second tone which, at each chosen = frequency, leads to a reduction of the response of the above-mentioned neur= on by exactly 20 percent.=20 =20 The lowest black circle is at 26 decibel, 10 kilohertz (i.e., 0.32 octave h= igher than 8 kilohertz). =20 This second tone leads to a strong basilar-membrane vibration at the 10-kil= ohertz characteristic place, about 1.5 mm basal of the 8-kilohertz characte= ristic place. At the 10-kilohertz place, the 8-kilohertz travelling wave st= arts to be amplified by the cochlear amplifier (i.e., by the outer hair cel= ls). That amplification is hindered by the 10-kilohertz vibration.=20 =20 The effects of the sound pressure levels can be inferred, e.g., from Fig. 1= 4 of the review "Mechanics of the Mammalian Cochlea", by Robles and Ruggero= [Physiological Review 81 (2001) 1305-1351]. =20 The curve of basilar-membrane displacement versus position has an "active" = peak, comparatively high at low sound pressure levels, and, a few millimetr= es basal, a "passive" peak, comparatively high at high sound pressure level= s. In humans, the distance between the two peaks is about 3 millimetres. =20 The active peak is comparatively weak at high levels because the outer hair= cells are "saturated", i.e., are unable to deliver the amplification facto= r which they deliver at lower levels. =20 Reinhart Frosch. Reinhart Frosch,=20 Dr. phil. nat.,=20 r. PSI and ETH Zurich,=20 Sommerhaldenstr. 5B,=20 CH-5200 Brugg.=20 Phone: 0041 56 441 77 72.=20 Mobile: 0041 79 754 30 32.=20 E-mail: reinifrosch@xxxxxxxx . ----Urspr=C3=BCngliche Nachricht---- Von: nshahnaz@xxxxxxxx Datum: 15.01.2007 17:46 An: <AUDITORY@xxxxxxxx> Betreff: Cochlear nonlinearity & TTS 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 f= unction of frequency for a given center frequency at multiple levels you wi= ll notice that first the cochlea will lose its nonlinearity at the best fre= quency at high levels and the best frequency shifts more toward the lower f= requencies (apicalward); however, when you look at travelling wave on the = BM for a given center frequency at multiple levels the best frequency shif= ts toward higher frequencies (basalward) with increasing levels (Ren, 2002)= . This level dependent shift has been proposed as an explanation for a shif= t in TTS. My question is why displacement of BM for the CF is more toward t= he apical side at high levels while the travelling wave is basalward. The = latter proposes that the amplifier should be more apical to the CF; therefo= re, damaging this area will result in a shift in threshold toward more basa= l 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/ ------=_Part_20868_11014811.1168951721542 Content-Type: text/html;charset="UTF-8" Content-Transfer-Encoding: quoted-printable <html><head><style type=3D'text/css'> <!-- #bwmail { background-color:#ffffff; font-family: Verdana,Arial,Helvetica; f= ont-size: 11px; margin:0; padding:0;} #bwmail p { margin:0; padding:0; } #bwmail table { font-family: Verdana,Arial,Helvetica; font-size: 11px; } #bwmail li { margin:0; padding:0; } --> </style> </head><body><div id=3D'bwmail'><P>Dear Navid and List,</P> <P> </P> <P>Two-tone suppression is explained, e.g., in Figure 1.21 of "An Introduct= ion to the Psychology of Hearing" by B.C.J. Moore (Academic Press, 5th edit= ion, 2003). Abscissa: frequency (of sine-tones). Ordinate: sound pressure l= evels. </P> <P> </P> <P>Open circles: tuning curve (threshold versus frequency) of a single neur= on with characteristic frequency of 8 kilohertz. Lowest point of tuning cur= ve: 8 kilohertz, 10 decibel.</P> <P> </P> <P>An open triangle indicates the first tone: sine-tone of 8 kilohertz, 27 = decibel.</P> <P> </P> <P>Black circles: sound pressure level of a second tone which, at each chos= en frequency, leads to a reduction of the response of the above-mentioned n= euron by exactly 20 percent. </P> <P> </P> <P>The lowest black circle is at 26 decibel, 10 kilohertz (i.e., 0.32 octav= e higher than 8 kilohertz).</P> <P> </P> <P>This second tone leads to a strong basilar-membrane vibration at the 10-= kilohertz characteristic place, about 1.5 mm basal of the 8-kilohertz chara= cteristic place. At the 10-kilohertz place, the 8-kilohertz travelling wave= starts to be amplified by the cochlear amplifier (i.e., by the outer hair = cells). That amplification is hindered by the 10-kilohertz vibration. </P> <P> </P> <P>The effects of the sound pressure levels can be inferred, e.g., from Fig= . 14 of the review "Mechanics of the Mammalian Cochlea", by Robles and Rugg= ero [Physiological Review 81 (2001) 1305-1351].</P> <P> </P> <P>The curve of basilar-membrane displacement versus position has an "activ= e" peak, comparatively high at low sound pressure levels, and, a few millim= etres basal, a "passive" peak, comparatively high at high sound pressure le= vels. In humans, the distance between the two peaks is about 3 millimetres.= </P> <P> </P> <P>The active peak is comparatively weak at high levels because the outer h= air cells are "saturated", i.e., are unable to deliver the amplification fa= ctor which they deliver at lower levels.</P> <P> </P> <P>Reinhart Frosch.</P> <P><BR><BR>Reinhart Frosch, <BR>Dr. phil. nat., <BR>r. PSI and ETH Zurich, = <BR>Sommerhaldenstr. 5B, <BR>CH-5200 Brugg. <BR>Phone: 0041 56 441 77 72. <= BR>Mobile: 0041 79 754 30 32. <BR>E-mail: reinifrosch@xxxxxxxx .<BR><BR><= BR>----Urspr=C3=BCngliche Nachricht----<BR>Von: nshahnaz@xxxxxxxx= <BR>Datum: 15.01.2007 17:46<BR>An: <AUDITORY@xxxxxxxx><BR>Betr= eff: Cochlear nonlinearity & TTS<BR><BR></P><!-- --> <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-FAM= ILY: Arial" width=3D"100%"> <DIV>Dear List</DIV> <DIV>I've been trying to find a good explanation on why TTS occur about hal= f an octave to an octave higher than than the exposure frequency. When you = look at BM displacement patterns (Johnstone, 1986; Ruggero et al.,&nb= sp;1997) as a function of frequency for a given center frequency at mu= ltiple levels you will notice that first the cochlea will lose its nonlinea= rity at the best frequency at high levels and the best frequency shift= s more toward the lower frequencies (apicalward); however, when you look at= travelling wave on the BM for a given center frequency at multiple l= evels the best frequency shifts toward higher frequencies (basalward)= with increasing levels (Ren, 2002). This level dependent shift has been pr= oposed as an explanation for a shift in TTS. My question is why displa= cement 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 ampli= fier should be more apical to the CF; therefore, damaging this area will re= sult in a shift in threshold toward more basal 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>Assistant P= rofessor<BR>School of Audiology & Speech Sciences<BR>Faculty of Medicin= e<BR>University of British Columbia<BR>5804 Fairview Ave., J. Mather Buildi= ng<BR>Vancouver, BC Canada V6T 1Z3<BR>Tel. 604- 822-5953<BR>Fax.604-822-656= 9<BR>E-mail: <A title=3Dmailto:nshahnaz@xxxxxxxx href=3D"mailto:n= shahnaz@xxxxxxxx">nshahnaz@xxxxxxxx</A></FONT></DIV> <DIV>Website:<A href=3D"http://www.audiospeech.ubc.ca/school/faculty/navid/= " target=3D_BLANK>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></TAB= LE></TD></TR></TBODY></TABLE><BR><BR></div></html> ------=_Part_20868_11014811.1168951721542--