Reconsidering evidence for the suppression model of the octave illusion

Abstract

The octave illusion is a compelling perceptual phenomenon that arises when each ear is presented with an alternating sequence of tones separated by one octave, but with the high-and the low-frequency tones in different ears (Figure 1). The majority of listeners are unable to accurately describe these stimuli and, instead, report a high pitch in one ear alternating with a low pitch in the opposite ear. Deutsch (1974) noted that, when presented with these stimuli via headphones, most listeners heard the higher pitch toward the right and the lower pitch toward the left. This trend was particularly salient for righthanded listeners, but not for left-handed listeners. Deutsch (1974) suggested that this handedness effect indexed the lateralization of the higher pitch "toward the side producing the most effective input to the dominant hemisphere" (p. 308).The unique and influential suppression model of this phenomenon was later proposed by Deutsch and Roll (1976). From an analysis of subjective reports, the authors suggested that the octave illusion arises from a high-frequency dominance for sound localization, combined with ear dominance for pitch in which the dominant ear "exercises a steady suppression on the other [ear], so that only the frequencies arriving at one ear are heard" (p. 24). According to this theory, the interplay of ear dominance for pitch and high-frequency dominance for localization results in conflict when the high-frequency tone is presented to the nondominant ear. Under this condition, Deutsch and Roll suggested that listeners perceive the pitch presented to their dominant ear but localize this percept in the opposite ear. The authors thus concluded that the octave illusion reveals separate neural mechanisms governing the what and where of auditory perception, which may be placed in conflict under appropriate conditions. Deutsch (1978, 1980a, 1988) later included a third tenet to the suppression model, suggesting that this unique division of object-and location-based auditory mechanisms was facilitated by sequential interactions between the tones-specifically, the repeated alternation of the same frequencies between the ears.A recent study by Chambers, Mattingley, and Moss (2002) has challenged the validity of the suppression model. From a psychophysical investigation, their results suggest instead that (1) the pitch variation during the octave illusion may arise from established mechanisms of harmonic fusion, (2) the high-frequency dominance for localization proposed by the suppression model regularly fails to emerge, and (3) both the pitch differences between alternate dichotic octaves 1 and the apparent lateralization of single dichotic octaves can occur indepen- The octave illusion is elicited by a sequence of tones presented to each ear that continuously alternate in frequency by one octave, but with high and low frequencies always in different ears. The percept for most listeners is a high pitch in one ear, alternating with a low pitch in the other ear. The influential suppression model o...

Reply to “Reconsidering evidence for the suppression model of the octave illusion,” by C. D. Chambers, J. B. Mattingley, and S. A. Moss

“…The size of the pitch difference that is characteristic of diplacusis generally corresponds to a fraction of a semitone (Van den Brink, 1975), so this hypothesis requires that pitch differences heard on listening to the octave illusion be very small. As is shown in Figure 12 of Chambers et al (2004), the size of pitch difference predicted from their hypothesis is indeed a frac- tion of a semitone. They write, "This finding implies that, if perceived synthetically, the pitch difference between the higher and the lower pitch dichotic octave might oscillate for this listener between 0.3% (1.2 Hz/400 Hz) and 2.3% (9.2 Hz/400 Hz)" (p. 660), and it should be noted that the pitch differences given here correspond to less than half a semitone.…”

“…This article replies to the main arguments raised by Chambers et al (2004). First, their discussion of the related literature makes inappropriate comparisons with other phenomena of sound perception and fails to consider several key findings that support the two-channel model.…”

“…This model, hereafter referred to as the two-channel model, assumes that the illusion results from a dissociation between what and where pathways in the auditory system. Chambers et al (2004) propose, instead, that the octave illusion results from a combination of binaural fusion and diplacusis.This article replies to the main arguments raised by Chambers et al (2004). First, their discussion of the related literature makes inappropriate comparisons with other phenomena of sound perception and fails to consider several key findings that support the two-channel model.…”

“…This model, hereafter referred to as the two-channel model, assumes that the illusion results from a dissociation between what and where pathways in the auditory system. Chambers et al (2004) propose, instead, that the octave illusion results from a combination of binaural fusion and diplacusis.…”

“…1 The findings from this experiment, in which explicit judgments were made using musical notation, and which also involved a matching procedure, are in accordance with those of Deutsch (1974) and Zwicker (1984) and are consistent with the two-channel model. Chambers et al (2004) advance the alternative hypothesis that pitch differences heard on listening to the octave illusion result from diplacusis, a slight pitch difference that may be perceived when the same tone is presented to the left and the right ears. The size of the pitch difference that is characteristic of diplacusis generally corresponds to a fraction of a semitone (Van den Brink, 1975), so this hypothesis requires that pitch differences heard on listening to the octave illusion be very small.…”