“Octave illusion” or “Deutsch’s illusion”?

Abstract

The "Deutsch's illusion" occurs in most people when a dichotic pair of tones spaced an octave apart is presented repeatedly in alternation, so that when the right ear receives the high tone, the left ear receives the low tone, and vice versa. The illusory percept consists typically in a single low tone heard at one ear alternating with a single high tone heard at the other ear. Here, we investigate whether the frequency interval between the tones and their duration play a role in the perception of the illusion. By testing 74 subjects we demonstrate that the illusion is not confined to tones spaced an octave apart but it is perceivable also with tones separated by a major seventh, a minor ninth, a major ninth, and a minor tenth. Regarding duration, the present results show that the illusion is stronger with tones lasting 500 than 200 ms. The present results suggest that the perceptual mechanisms at the basis of the illusion are not strictly linked to the frequency relationships between the dichotic tones.

Octave illusion elicited by overlapping narrowband noises

“…1). This phenomenon was first described by Deutsch (1974) and appears to be restricted not only to tones that are separated by an octave but can also to that occur with larger and smaller intervals (Zwicker, 1984;Brancucci et al, 2009). As shown in the lower portion of Fig.…”

“…Furthermore, the mechanisms of binaural diplacusis and harmonic binaural fusion proposed by Chambers and colleagues can be questioned on the basis of previous research using pure-tone stimuli, which showed that Deutsch's illusion can be elicited by intervals smaller than an octave (Zwicker, 1984;Brancucci et al, 2009). Furthermore, Brancucci and colleagues showed that the salience of Deutsch's illusion decreased with reduced frequency separation between pure tones (Brancucci et al, 2009).…”

“…Furthermore, Brancucci and colleagues showed that the salience of Deutsch's illusion decreased with reduced frequency separation between pure tones (Brancucci et al, 2009). This is problematic for an illusion elicited by binaural diplacusis and harmonic binaural fusion, since in Brancucci's study only a few subjects perceived the illusion for sequences of tones forming small frequency ratios (e.g., 400 and 480 Hz).…”

“…We used a three-interval forced-choice (3IFC) test paradigm previously used by (Zwicker 1984), while most research has mainly been conducted using a two-alternative forced-choice (2AFC) (Deutsch, 1978(Deutsch, , 1980(Deutsch, , 1988Chambers et al, 2002;Sonnadara and Trainor, 2005;Brancucci et al, 2009), qualitative responses (Deutsch, 1975b;Deutsch and Roll, 1976;Chambers et al, 2002;Deutsch, 2004a), or four-interval forced-choice (4IFC) by the subjects on the presented stimuli (Deutsch, 1983b). However, since previous research has shown that some subjects obtain different types of percept (e.g., Deutsch, 1974Deutsch, , 1983a, we decided to use 3IFC in order to minimize the bias produced by including such subjects, as would have been the consequence if we had used 2AFC test paradigm.…”

“…The pattern can also give rise to different auditory percepts (Deutsch, 1974;Craig, 1979;Deutsch, 1983a;Zwicker, 1984). Durations of about 200-500 ms, without gaps between tones within a pair, appear to produce the most salient percept of the illusion (Deutsch, 1983a;Zwicker, 1984;Brancucci et al, 2009), and longer interstimulus intervals appear to reduce its saliency (Deutsch, 1983a;Zwicker, 1984;Deutsch and Roll, 1976).…”