Interesting dichotic effect (Mitchell Sommers )


Subject: Interesting dichotic effect
From:    Mitchell Sommers  <msommers(at)ARTSCI.WUSTL.EDU>
Date:    Wed, 24 Jan 2001 13:41:00 -0600

This is a multi-part message in MIME format. ------=_NextPart_000_001B_01C0860B.49B5FE40 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable I wonder if anyone has any thoughts or knows of relevant research for = the following phenomenon. In the course of calibrating headphones for a = dichotic listening task, we generated stimuli consisting of two pure = tones. The stimuli were presented as follows. Stimulus 1 presented to = the right ear had equal-amplitude tones at 100 and 150 Hz. Stimulus 2 = presented to the left ear had equal-amplitude tones (same amplitude as = in stimulus 1) of 200 and 250 Hz. Stimuli 3 and 4 were simply the = reverse of these two ( left ear gets 100 and 150; right ear gets 200 and = 250). The rationale behind playing with these stimuli was that = "perfect" integration across the two ears should produce the identical = percept for both pairs of tones. That is, stimuli 1 and 2 presented = dichotically, should sound identical to stimuli 3 and 4 presented = dichotically because the spectral content is the same, we just switched = the ear to which each was presented. Instead, the perceptual experience = was a change in pitch. Interestingly of 4 listeners 2 perceived a = decrease in pitch and 2 perceived an increase (i.e., when 3 and 4 were = presented dichotically after hearing 1 and 2, there was either a = decrease or increase in pitch). We then tried simply reversing the = headphones (left transducer on right ear and vice-versa) and the = perception was the same. We also tried a different combination such = that stimulus 1 had equal-amplitude components at 100 and 400 Hz and = stimulus 2 had equal amplitude components at 200 and 300 Hz. Again, the = perception was a pitch change when we switched channels for stimulus 1 = and 2. I'd be interested in any ideas as to why we would get a clear = pitch change using this stimulus configuration. Many thanks Mitch Sommers Mitchell S. Sommers, Ph.D. Associate Professor Department of Psychology Washington University Campus Box 1125 St. Louis, MO 63130 E-mail: msommers(at)artsci.wustl.edu Phone: 314-935-6561 Fax:: 314-935-7588 ------=_NextPart_000_001B_01C0860B.49B5FE40 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD> <META content=3D"text/html; charset=3Diso-8859-1" = http-equiv=3DContent-Type> <META content=3D"MSHTML 5.00.2614.3500" name=3DGENERATOR> <STYLE></STYLE> </HEAD> <BODY bgColor=3D#ffff00> <DIV>I wonder if anyone has any thoughts or knows of relevant research = for the=20 following phenomenon.&nbsp; In the course of calibrating headphones for = a=20 dichotic listening task, we generated stimuli consisting of two pure=20 tones.&nbsp; The stimuli were presented as follows.&nbsp; Stimulus 1 = presented=20 to the right ear had equal-amplitude tones at 100 and 150 Hz.&nbsp; = Stimulus 2=20 presented to the left ear had equal-amplitude tones (same amplitude as = in=20 stimulus 1) of 200 and 250 Hz.&nbsp;&nbsp;&nbsp; Stimuli 3 and 4 were = simply the=20 reverse of these two ( left ear gets 100 and 150; right ear gets 200 and = 250).&nbsp; The rationale behind playing with these stimuli was that = "perfect"=20 integration across the two ears should produce the identical percept for = both=20 pairs of tones.&nbsp; That is, stimuli 1 and 2 presented dichotically, = should=20 sound identical to stimuli 3 and 4 presented dichotically because the = spectral=20 content is the same, we just switched the ear to which each was = presented.&nbsp;=20 Instead, the perceptual experience was a change in pitch.&nbsp; = Interestingly of=20 4 listeners 2 perceived a decrease in pitch and 2 perceived an increase = (i.e.,=20 when 3 and 4 were presented dichotically after hearing 1 and 2, there = was either=20 a decrease or increase in pitch).&nbsp; We then tried simply reversing = the=20 headphones (left transducer on right ear and vice-versa) and the = perception was=20 the same.&nbsp; We also tried a different combination such that stimulus = 1 had=20 equal-amplitude components at 100 and 400 Hz and stimulus 2 had equal = amplitude=20 components at 200 and 300 Hz.&nbsp; Again, the perception was = a&nbsp;pitch=20 change when we switched channels for stimulus 1 and 2.&nbsp; I'd be = interested=20 in any ideas as to why we would get a clear pitch change using this = stimulus=20 configuration.&nbsp; Many thanks</DIV> <DIV>&nbsp;</DIV> <DIV>Mitch Sommers</DIV> <DIV>&nbsp;</DIV> <DIV>&nbsp;</DIV> <DIV>&nbsp;</DIV> <DIV>Mitchell S. Sommers, Ph.D.<BR>Associate Professor<BR>Department of=20 Psychology<BR>Washington University<BR>Campus Box 1125<BR>St. Louis, MO=20 63130</DIV> <DIV>&nbsp;</DIV> <DIV>E-mail: <A=20 href=3D"mailto:msommers(at)artsci.wustl.edu">msommers(at)artsci.wustl.edu</A><B= R>Phone:=20 314-935-6561<BR>Fax::&nbsp; 314-935-7588</DIV> <DIV>&nbsp;</DIV> <DIV>&nbsp;</DIV></BODY></HTML> ------=_NextPart_000_001B_01C0860B.49B5FE40--


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