The octave illusion revisited: suppression or fusion between ears?

The octave illusion occurs when each ear receives a sequence of tones alternating by 1 octave but with the high and low tones in different ears. Most listeners perceive these stimuli as a high pitch in one ear alternating with a low pitch in the other ear. D. Deutsch and P. L. Roll (1976) interpreted this phenomenon as evidence for a what-where division of auditory processing caused by sequential interactions between the tones. They argued that the pitch follows the frequency presented to the dominant ear but is lateralized toward the higher frequency component. This model was examined in 4 experiments. Results indicate that the perceived pitch approximates the fundamental frequency and that the illusion does not depend on sequential interactions. The octave illusion may arise from an interaction between dichotic fusion and binaural diplacusis rather than from suppression as proposed by Deutsch.     

Does selective attention influence the octave illusion?

The octave illusion occurs when each ear receives a sequence of tones alternating by one octave, but with different frequencies in each ear. Most listeners report a high pitch in one ear alternating with a low pitch in the opposite ear. Deutsch and Roll proposed an influential suppression model of the illusion in which the pitch is determined by ear dominance, while the location of this pitch is determined by high-frequency dominance. Deutsch later suggested that this unusual division between 'what' and 'where' mechanisms is facilitated by sequential interactions within the eliciting sequence. A recent study has raised doubts about the suppression model and the role of sequential interactions in the illusion (Chambers et al, 2002 Journal of Experimental Psychology: Human Perception and Performance 28 1288-1302). Here, we examined whether this previous null effect of sequential interactions may have arisen because of uncontrolled influences of selective attention. The results reveal no evidence of a link between selective attention and sequential interactions, thus consolidating doubts about the validity of the suppression model.     

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

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.     

Specialist musical training and the octave illusion: analytical listening and veridical perception by pipe organists

The octave illusion is a useful tool for investigation of the contribution of specialist training to auditory perception. The stimulus that induces the illusion involves two tones with a frequency ratio of 2:1, presented dichotically, and with ear of presentation reversed every 250 ms. Most listeners report hearing a single tone that alternates from high in the right ear to low in the left ear [Scientific American 233 (1975) 92-104]. The first experiment investigated the hypothesis that musical training contributes to veridical perception of an ambiguous stimulus. As hypothesized, participants with the highest level of musical training were more likely to perceive the stimulus veridically. Exploring the effects of specialist training, Experiment 2 contrasted expert pipe organists with other instrumentalists. As hypothesized, participants expert in playing pipe organ--an instrument with harmonic and spatial features similar to those of the octave illusion--were more likely to perceive the stimulus veridically. The results have implications for plasticity of the auditory system and the analytical listening that accompanies specialist, intensive training and rehearsal.     

The octave illusion revisited again

The octave illusion (D. Deutsch, 1974) occurs when 2 tones separated by an octave are alternated repeatedly, such that when the right ear receives the high tone, the left ear receives the low tone, and vice versa. Most subjects in the original study reported hearing a single tone that alternated from ear to ear, whose pitch also alternated from octave to octave, and D. Deutsch (1975a) proposed an explanation in terms of separate what and where auditory pathways. C. D. Chambers, J. B. Mattingley, and S. A. Moss (2002) argued that the perceived pitch difference generally corresponds more to a semitone and proposed an alternative explanation in terms of diplacusis. This article argues that Chambers et al. used problematic procedures and reports a new experiment on the octave illusion. The findings confirm that an octave difference is generally perceived, and they agree with the model of Deutsch (1975a) but are at variance with the diplacusis hypothesis.     

Circularity in relative pitch judgments for inharmonic complex tones: The Shepard demonstration revisited,again

The Shepard illusion, in which the presentation of a cyclically repetitive sequence of complex tones composed of partials separated by octave intervals (Shepard, 1964) gives the illusion of an endlessly increasing sequence of pitch steps, is often cited as evidence for octave equivalence. In this paper, evidence is presented which demonstrates that this illusion can be produced using (inharmonic) complex tones whose partials are separated by equal ratios other than octaves. Therefore, the illusion is not evidence for octave equivalence.     

Perceived intensity effects in the octave illusion

We showed that there is an intensity aspect to the octave illusion in addition to the pitch and location aspects originally reported by Deutsch (1974). In Experiment 1, we asked participants to directly compare the stimulus giving rise to the illusion (ILLU) with one mimicking its most commonly reported percept (illusion consistent; IC) and showed that they were easily able to distinguish between the two. In Experiment 2, we demonstrated a clear difference between the perceived loudness of ILLU and IC when IC follows ILLU, but not when IC precedes ILLU. In Experiments 3 and 4, we showed that this effect depends on the alternation of high and low tones between the ears in an extended pattern. In Experiment 5, we showed that this difference in perceived loudness disappears if the interval between the ILLU and IC stimuli is sufficiently large.     

Perceptual hysteresis in the judgment of auditory pitch shift

Perceptual hysteresis can be defined as the enduring influence of the recent past on current perception. Here, hysteresis was investigated in a basic auditory task: pitch comparisons between successive tones. On each trial, listeners were presented with pairs of tones and asked to report the direction of subjective pitch shift, as either “up” or “down.” All tones were complexes known as Shepard tones (Shepard, 1964), which comprise several frequency components at octave multiples of a base frequency. The results showed that perceptual judgments were determined both by stimulus-related factors (the interval ratio between the base frequencies within a pair) and by recent context (the intervals in the two previous trials). When tones were presented in ordered sequences, for which the frequency interval between tones was varied in a progressive manner, strong hysteresis was found. In particular, ambiguous stimuli that led to equal probabilities of “up” and “down” responses within a randomized context were almost fully determined within an ordered context. Moreover, hysteresis did not act on the direction of the reported pitch shift, but rather on the perceptual representation of each tone. Thus, hysteresis could be observed within sequences in which listeners varied between “up” and “down” responses, enabling us to largely rule out confounds related to response bias. The strength of the perceptual hysteresis observed suggests that the ongoing context may have a substantial influence on fundamental aspects of auditory perception, such as how we perceive the changes in pitch between successive sounds.     

Quantification of the hierarchy of tonal functions within a diatonic context

Listeners rated test tones falling in the octave range from middle to high C according to how well each completed a diatonic C major scale played in an adjacent octave just before the final test tone. Ratings were well explained in terms of three factors. The factors were distance in pitch height from the context tones, octave equivalence, and the following hierarchy of tonal functions: tonic tone, other tones of the major triad chord, other tones of a diatonic scale, and the nondiatonic tones. In these ratings, pitch height was more prominent for less musical listeners or with less musical (sinusoidal) tones, whereas octave equivalence and the tonal hierarchy prevailed for musical listeners, especially with harmonically richer tones. Ratings for quarter tones interpolated halfway between the halftone steps of the standard chromatic scale were approximately the averages of ratings for adjacent chromatic tones, suggesting failure to discriminate tones at this fine level of division.     

Acquisition of the hierarchy of tonal functions in music

The acquisition of the hierarchy of tonal stabilities in music is investigated in children of elementary school age. Listeners judge how good short tone sequences sound as melodies. The ratings show a pattern of increasing differentiation of the pitches in an octave range. The youngest listeners distinguish between scale and nonscale tones; older listeners distinguish between the tonic triad tones and other scale components. A group of adult listeners show octave equivalence and temporal asymmetries, with a preference for sequences ending on the more stable tones within the hierarchy. Pitch height effects do not interact with the age of the listener. These results are discussed in terms of the primacy of physical variables, novice-expert differences, and general cognitive principles governing the acquisition and development of internal representations of pitch relationships.     

Responsiveness of Western adults to pitch-distributional information in melodic sequences

Responsiveness of musically trained and untrained adults to pitch-distributional information in melodic contexts was assessed. In Experiment 1, melodic contexts were pure-tone sequences, generated from either a diatonic or one of four nondiatonic tonesets, in which pitch-distributional information was manipulated by variation of the relative frequency of occurrence of tones from the toneset. Both the assignment of relative frequency of occurrence to tones and the construction of the (fixed) temporal order of tones within the sequences contravened the conventions of western tonal music. A probe-tone technique was employed. Each presentation of a sequence was followed by a probe tone, one of the 12 chromatic notes within the octave. Listeners rated the goodness of musical fit of the probe tone to the sequence. Probe-tone ratings were significantly related to frequency of occurrence of the probe tone in the sequence for both trained and untrained listeners. In addition, probe-tone ratings decreased as the pitch distance between the probe tone and the final tone of the sequence increased. For musically trained listeners, probe-tone ratings for diatonic sequences tended also to reflect the influence of an internalized tonal schema. Experiment 2 demonstrated that the temporal location of tones in the sequences could not alone account for the effect of frequency of occurrence in Experiment 1. Experiment 3 tested musically untrained listeners under the conditions of Experiment 1, with the exception that the temporal order of tones in each sequence was randomized across trials. The effect of frequency of occurrence found in Experiment 1 was replicated and strengthened.     

The subjective size of melodic intervals over a two-octave range

Musically trained and untrained participants provided magnitude estimates of the size of melodic intervals. Each interval was formed by a sequence of two pitches that differed by between 50 cents (one half of a semitone) and 2,400 cents (two octaves) and was presented in a high or a low pitch register and in an ascending or a descending direction. Estimates were larger for intervals in the high pitch register than for those in the low pitch register and for descending intervals than for ascending intervals. Ascending intervals were perceived as larger than descending intervals when presented in a high pitch register, but descending intervals were perceived as larger than ascending intervals when presented in a low pitch register. For intervals up to an octave in size, differentiation of intervals was greater for trained listeners than for untrained listeners. We discuss the implications for psychophysical pitch scales and models of music perception.     

Dynamic frequency change influences loudness perception: a central, analytic process.

Three experiments showed that dynamic frequency change influenced loudness. Listeners heard tones that had concurrent frequency and intensity change and tracked loudness while ignoring pitch. Dynamic frequency change significantly influenced loudness. A control experiment showed that the effect depended on dynamic change and was opposite that predicted by static equal loudness contours. In a 3rd experiment, listeners heard white noise intensity change in one ear and harmonic frequency change in the other and tracked the loudness of the noise while ignoring the harmonic tone. Findings suggest that the dynamic interaction of pitch and loudness occurs centrally in the auditory system; is an analytic process; has evolved to take advantage of naturally occurring covariation of frequency and intensity; and reflects a shortcoming of traditional static models of loudness perception in a dynamic natural setting.     

Generality of interference by tonal stimuli in recognition memory for pitch

An investigation was made into the disruptive effects on pitch recognition produced by tones taken from beyond the octave from which the standard (S) and comparison (C) tones were taken. Pitch recognition was required after a retention interval during which eight other tones were played. Errors were compared for sequences in which the interpolated tones were taken from the same octave as were the S and C tones; in which they were taken from the octave above; in which they were taken from the octave below; and in which half of the intervening tones were taken from the octave above and the other half from the octave below, the order of choice of octave within the sequence being random. Large disruptive effects were produced by interpolated tones drawn from the higher and lower octaves, though these effects were slightly less than those produced by tones drawn from the same octave. The greatest disruptive effect occurred when the intervening tones in any one sequence were drawn from both the higher and the lower octaves. The implications of these findings are discussed.     

Frequency-shift detectors bind binaural as well as monaural frequency representations

Previous psychophysical work provided evidence for the existence of automatic frequency-shift detectors (FSDs) that establish perceptual links between successive sounds. In this study, we investigated the characteristics of the FSDs with respect to the binaural system. Listeners were presented with sound sequences consisting of a chord of pure tones followed by a single test tone. Two tasks were performed. In the "present/absent" task, the test tone was either identical to one of the chord components or positioned halfway in frequency between two components, and listeners had to discriminate between these two possibilities. In the "up/down" task, the test tone was slightly different in frequency from one of the chord components and listeners had to identify the direction (up or down) of the corresponding shift. When the test tone was a pure tone presented monaurally, either to the same ear as the chord or to the opposite ear, listeners performed the up/down task better than the present/absent task. This paradoxical advantage for directional frequency shifts, providing evidence for FSDs, persisted when the test tone was replaced by a dichotic stimulus consisting of noise but evoking a pitch sensation as a consequence of binaural processing. Performance in the up/down task was similar for the dichotic stimulus and for a monaural narrow-band noise matched in pitch salience to it. Our results indicate that the FSDs are insensitive to sound localization mechanisms and operate on central frequency representations, at or above the level of convergence of the monaural auditory pathways.     

Ear of input as a determinant of pitch-memory interference

Six experiments to evaluate the effect of presentation ear on pitch-memory interference were conducted using undergraduates as listeners. The task was to compare the pitch of two tones that were separated by an interval that included eight interpolated tones; the interpolated tones were presented either ipsilaterally or contralaterally to the presentation ear of the comparison tones. When the ear of interpolated-tone presentations was blocked, and therefore predictable, ipsilateral interference was greater than contralateral. In contrast, when the interpolated-tone presentation ear was varied randomly from trial to trial, ipsilateral and contralateral interferences were equivalent. These results are analogous to results found in previously reported auditory backward recognition masking (ABRM) experiments and suggest that the ABRM effect may be due, in part, to pitch-memory interference. Implications for theories of auditory processing and memory are discussed.     

Hemisphere differences in an auditory Stroop test

In an auditory Stroop test, right-handed subjects were required to judge the pitch of the following stimuli: two pure tones, one at a high frequency and one at a low frequency; two congruent words, “high,” sung at the high frequency, and “low,” sung at the low frequency; and two noncongruent words, “high” at low frequency and “low” at high frequency. A sequence of these stimuli was presented monaurally first to one ear, and then to the other. The Stroop effect (the difference between mean RT to congruent words, and mean RT to noncongruent words) was larger for right ear (left hemisphere) presentation. The same experiment was repeated dichotically with a competing message presented to the opposite ear. Again, the Stroop effect was larger for the right ear, and the ear differences were slightly more marked. The result is interpreted as reflecting hemispheric specialization for linguistic and nonlinguistic processing and a model of Stroop conflict in which response competition varies with the relative availability of the conflicting response.

     

Perception of relative pitch with different references: Some absolute-pitch listeners can’t tell musical interval names

Two experiments were conducted to examine the effect of absolute-pitch possession on relativepitch processing. Listeners attempted to identify melodic intervals ranging from a semitone to an octave with different reference tones. Listeners with absolute pitch showed declined performance when the reference was out-of-tune C, out-of-tune E, or F#, relative to when the reference was C. In contrast, listeners who had no absolute pitch maintained relatively high performance in all reference conditions. These results suggest that absolute-pitch listeners are weak in relative-pitch processing and show a tendency to rely on absolute pitch in relative-pitch tasks.     

Schema-based processing in auditory scene analysis

What is the involvement of what we know in what we perceive? In this article, the contribution of melodic schema-based processes to the perceptual organization of tone sequences is examined. Two unfamiliar six-tone melodies, one of which was interleaved with distractor tones, were presented successively to listeners who were required to decide whether the melodies were identical or different. In one condition, the comparison melody was presented after the mixed sequence: a target melody interleaved with distractor tones. In another condition, it was presented beforehand, so that the listeners had precise knowledge about the melody to be extracted from the mixture. In the latter condition, recognition performance was better and a bias toward same responses was reduced, as compared with the former condition. A third condition, in which the comparison melody presented beforehand was transposed up in frequency, revealed that whereas the performance improvement was explained in part by absolute pitch or frequency priming, relative pitch representation (interval and/or contour structure) may also have played a role. Differences in performance as a function of mean frequency separation between target and distractor sequences, when listeners did or did not have prior knowledge about the target melody, argue for a functional distinction between primitive and schema-based processes in auditory scene analysis.     

Interference in pitch memory as a function of ear or input

An experiment was conducted to investigate the effect of spatial separation on interference effects in pitch memory. Subjects compared the pitches of two tones that were separated by a sequence of eight interpolated tones. It was found that error rates were lower in sequences where the test and interpolated tones were presented to different ears, compared with sequences where they were presented to the same ear; however, this effect of spatial separation was not large. It is concluded that differences in spatial location can enable the focussing of attention away from the irrelevant tones and so reduce their disruptive effect, but that this occurs only to a limited extent.