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Re: Interesting dichotic effect

  I haven't had time to give this a lot of thought, but maybe it has
something to do with a laterality effect.  I seem to remember the suggestion
by Sidtis that some aspects of pitch perception are lateralized to the right
hemifield.  It may then be the differences are due to differences in
processing across hemifields (assuming stronger crossed pathways than
uncrossed pathways). Anyway, here are the references:

Sidtis, J. (1980).  On the nature of the cortical function underlying right
hemisphere auditory perception.  Neuropsychologia 18:321-330.

Sidtis, J. J. (1981).  The complex tone test: Implications for the
assessment of auditory laterality effects.  Neuropsychologia 19:103-112.


Robert S. Bolia
Air Force Research Laboratory (AFRL/HECP)
2255 H Street
Wright-Patterson Air Force Base, OH 45433-7022
Phone: (937) 255-8802
FAX: (937) 255-8752
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From: Mitchell Sommers <msommers@ARTSCI.WUSTL.EDU>
Reply-To: Mitchell Sommers <msommers@ARTSCI.WUSTL.EDU>
Subject: Interesting dichotic effect
Date: Wed, 24 Jan 2001 13:41:00 -0600

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@artsci.wustl.edu
Phone: 314-935-6561
Fax::  314-935-7588

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