interesting dichotic effect

[Diana Deutsch <ddeutsch@xxxxxxxx>]

The effect you describe is related to the octave illusion, which I first
reported using tones at 400 and 800 Hz at the Spring, 1974 meeting of the
Acoustical Society, and in  Nature, 1974, 251, 307-309 (was it really that
long ago??). Basically, both ears receive a sequence of sine wave tones
alternating between  400 Hz and 800 Hz; however when the right ear receives
400 Hz the left ear receives 800 Hz, and vice versa. The perception differs
from one listener to another, but most righthanders hear a high tone on the
right alternating with a low tone on the left, and maintain this percept
when the earphone positions are reversed. (It's important, when you set the
illusion up, to ensure that there is phase continuity between the
alternating tones in each channel, and also that the switching ocurs in
strict synchrony.)

For investigations into the bases of the octave illusion, and its
perceptual correlates, see my articles  in the Journal of Experimental
Psychology: Human Perception and Performance 1976, 2, 23-29 (Deutsch and
Roll);  JASA, 1978, 63, 184-186; JASA, 1980, 67, 220-228; 'The octave
illusion and auditory perceptual integration' in Tobias, J. V.  and
Schubert, E. D. (Eds), Hearing Research and Theory Vol 1, Academic Press
1981, 99-142; 'The octave illusion and the what-where connection' in R. S.
Nickerson (Ed) Attention and Performance VIII, 1980, 575-594;
Neuropsychologia 1983, 31, 607-618; and JASA, 1988, 83, 365-368. The effect
is enhanced whan you play this alternating pattern repeatedly (see JASA,
1978, 1980, 1988, and the review articles), and the way it is perceived
varies in correlation with the listener's handedness (see the articles in
Nature and Neuropsychologia). For more popular accounts see my articles
'Musical Illusions' Scientific American 1975, 233, 92-104, and 'Illusions
for stereo headphones' Audio Magazine March 1987, 36-48. The octave
illusion is featured on a number of compact discs, including  'Auditory
demonstrations' (Houtsma, Rossing and Wagenaars, published by the
Acoustical Society of America  and Philips, 1987) and 'Musical Illusions
and Paradoxes' (published by Philomel Records, 1995, see
http://philomel.com).


Another interesting series of studies related to the effect you describe
was performed by Efron, Yund, and colleagues.

Diana Deutsch


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


Diana Deutsch
Professor of Psychology
Department of Psychology
University of California, San Diego
La Jolla, CA 92093, USA

tel:       858-453-1558
fax:      858-453-4763
e-mail: ddeutsch@ucsd.edu
            dd@philomel.com