Subject: interesting dichotic effect From: Diana Deutsch <ddeutsch(at)UCSD.EDU> Date: Wed, 24 Jan 2001 13:27:52 -0800The 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(at)ucsd.edu dd(at)philomel.com