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

Abstract

Chambers, Mattingley, and Moss (2004) review research and theory concerning the octave illusion, a phenomenon that was originally reported by Deutsch (1974) and that is characterized by substantial individual differences in perception. The authors argue against a model proposed by Deutsch (1975a) to explain the illusory percept most commonly obtained. 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. Second, their methodological criticisms of experiments that support the two-channel model are based on misinterpretations of the experimental designs that were employed. Third, recent findings they cite from their laboratory were based on procedures that raise problems. Fourth, the fusion-diplacusis explanation for the octave illusion is inconsistent with the available evidence. Finally, the twochannel model is in accordance with the growing evidence for what-where dissociations in the auditory system and for illusory conjunctions in hearing.The pattern that was originally employed to produce the octave illusion is illustrated in Figure 1. Two tones, at 400 and 800 Hz, were repeatedly presented in alternation. The tones were delivered to both ears simultaneously; however, when the right ear received 400 Hz the left ear received 800 Hz, and vice versa. The tones were 250-msec sine waves and were presented at equal amplitude, with no amplitude drops at the transitions between tones. Eighty-six naive subjects were presented with this pattern, and they reported what they heard.Substantial individual differences were found in the way this pattern was perceived, so the percepts were divided into three categories. The first type, termed octave, was obtained by the majority of the subjects and consisted of a single tone that alternated between ears, whose pitch also alternated between one octave and the other (so that a high tone was heard in one ear, alternating with a low tone in the other ear). For most of the subjects, the perceived locations of the high and low tones remained fixed when the earphone positions were reversed. The second type, termed single pitch, consisted of a single tone that alternated between ears, whose pitch either remained constant or shifted only slightly with a change in the perceived location of the tone. The third type, termed complex, consisted of a mixed group of complex percepts, which often involved three different pitches and tended to change with continued listening.The two-channel model, which was proposed to explain the octave category of percept, is illustrated in Figu...

Octave illusion elicited by overlapping narrowband noises

“…For the latter effect they have no straightforward explanation; they found that the subjects lateralized the tones sometimes to the ear receiving the high-frequency tone and sometimes to the ear receiving the low-frequency tone (Chambers et al, 2002). Based on these findings they suggested that lateralization patterns originate from processing in low-level areas for binaural integration, with possible interaction with higher-level processes (Chambers et al, 2002;Chambers and Mattingley, 2004) (but see Deutsch, 2004b for a rebuttal).…”

Ear and pitch segregation in Deutsch’s octave illusion persist following switch from stimulus alternation to repetition

“…[3][4][5][6][7][8][9][10][11][12] In addition, Deutsch 13 proposed a two-channel model to explain the octave illusion in terms of separate "what" and "where" decision mechanisms: The "what" mechanism determines that the perceived pitches are equivalent to the frequencies presented to the dominant ear, while the frequencies presented to the nondominant ear are suppressed; the "where" mechanism determines that percepts are localized at the ear receiving the higher frequency, regardless of which frequency is in fact perceived. 2,4,5,14,15 An alternative to the two-channel model was advanced more than 25 years later by Chambers and colleagues, 16,17 who proposed that the pitch variation experienced during listening to the octave illusion may arise from mechanisms of harmonic fusion combined with binaural diplacusis. Concerning the localization pattern, Chambers and colleagues claimed that this was not determined by the ear receiving the higher frequency; instead, they argued that the perceived tones were sometimes lateralized to the ear receiving the higher frequency and sometimes to the ear receiving the lower frequency.…”

“…8,15 More specifically, it was found that sequential relationships between the frequencies presented to the two ears influence the lateralization effect, i.e., the illusory alternating location of the tonal percept, and also the "ear dominance effect"; i.e., which ear is followed for pitch. 2 On the other hand, Chambers and colleagues 16,17 state that sequential effects did not influence the illusion (although see Deutsch 5,15 for further discussion of this issue).…”

The octave illusion and handedness: A replication of Deutsch’s 1974 study

“…There has also been a vivid discussion about the fundamental perceptual mechanisms of the octave illusion, especially the validity of the suppression model (Chambers, Mattingley, & Moss, 2002, 2004a, 2004bDeutsch, 1975Deutsch, , 2004b.…”