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In arbitrating between representational and relational theories of perception, perceptual illusions—cases in which a subject’s perceptual experience diverges from the way the world really is—constitute an important battleground. The debate has, however, been dominated by discussions of visual perception. In attempting to extend the debate to audition, it is appropriate to start by considering what is thought to be a key case of auditory illusion. I consider the phenomenon of the ‘missing fundamental’, as well as examining a notion that is often deployed by representationalists to explain it—namely, perceptual inference. Though it is frequently deployed as an explanatory concept by inferentialists, the notion of perceptual inference is somewhat opaque. Here, I formulate a ‘job description’ for perceptual inference, involving rule-following. I then identify two sets of cases that commonly prompt the invocation of perceptual inference: namely, cases of perceptual illusion, and cases of veridical perception where the perceptual content outstrips the information present in the stimulus. I then argue that an appeal to perceptual inference is unnecessary, in the case of the missing fundamental, for two reasons. Firstly, the missing fundamental is not, after all, a clear candidate for the ascription of inferential capacity to the auditory system: it is neither an illusion, nor is it the case that the stimulus is crucially impoverished. That is, it submits to a ‘direct’ explanation. Secondly, given the adequacy of a simpler explanation, and the difficulty between distinguishing between real rule-following and the mere appearance of it, I argue that we should avoid ascribing inferential capacity to the auditory system. I close by considering objections, and offering replies.

Background: There is evidence that experimentally elicited auditory illusions in the general population index risk for psychotic symptoms. As little is known about underlying cortical mechanisms of auditory illusions, an experiment was conducted to analyze processing of auditory illusions in a general population sample. In a follow-up design with two measurement moments (baseline and 6 months), participants (n = 83) underwent the White Noise task under simultaneous recording with a 14-lead EEG. An auditory illusion was defined as hearing any speech in a sound fragment containing white noise. Results: A total number of 256 speech illusions (SI) were observed over the two measurements, with a high degree of stability of SI over time. There were 7 main effects of speech illusion on the EEG alpha band-the most significant indicating a decrease in activity at T3 (t = -4.05). Other EEG frequency bands (slow beta, fast beta, gamma, delta, theta) showed no significant associations with SI. Conclusion: SIs are characterized by reduced alpha activity in non-clinical populations. Given the association of SIs with psychosis, follow-up research is required to examine the possibility of reduced alpha activity mediating SIs in high risk and symptomatic populations.

In music that is perceived as metrically structured, events coinciding with the main beat are called metrically accented. Are these accents purely cognitive, or do they perhaps represent illusory increases in perceived loudness or duration, caused by heightened attention to main beats? In four separate tasks, musicians tried to detect a small actual increase or decrease in the loudness or duration of a single note in melodies comprising 12 notes. Musical notation prescribed a meter (6/8) implying a main beat coinciding with every third note. Effects of metrical accentuation on detection performance were found in all four tasks. However, they reflected primarily an increase in sensitivity to physical changes in main beat positions, likely to be due to enhanced attention. There was no evidence of biases indicating illusory phenomenal accents in those positions. By contrast, and independent of metrical structure, pitch accents due to pitch contour pivots were often mistaken for increases in loudness.

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.

When a long glide with a short temporal gap in its middle crosses with a continuous short glide at the temporal midpoint of both glides, the gap is perceived in the short glide instead of in the long glide. In the present article, we tested possible explanations for this “gap transfer illusion” by obtaining points of subjective equality of the pitches and durations of the two short tones that are subjectively divided by the gap. The results of two experiments showed that neither an explanation in terms of envelope patterns nor explanations in terms of combination tones or acoustic beats could account for the perception of the short tones in the gap transfer illusion. Rather, the results were compatible with the idea that the illusory tones were formed by the perceptual integration of onsets and offsets of acoustically different sounds. Implications for the perceptual construction of auditory events are discussed.

Are the conditions for illusory auditory continuity entirely local in frequency, or are judgments of continuity made on auditory objects? Listeners made continuous/pulsating judgments on a variety of complex tones that repeatedly alternated with a 100- to 500-Hz bandpass noise. A sufficiently quiet complex tone was heard as continuous when all its harmonics fell within the frequency range of the noise. Adding harmonics outside the noise's frequency range substantially reduced the impression of continuity, which was largely restored when these additional components were given a different fundamental frequency. Judgments of auditory continuity thus appear to be based on entire simultaneously grouped objects, rather than being determined solely by local criteria based on individual frequency channels.

In four experiments, we investigated the influence of timbre on perceived interval size. In Experiment 1, musically untrained participants heard two successive tones and rated the pitch distance between them. Tones were separated by six or seven semitones and varied in timbre. Pitch changes were accompanied by a congruent timbre change (e.g., ascending interval involving a shift from a dull to a bright timbre), an incongruent timbre change (e.g., ascending interval involving a shift from a bright to a dull timbre), or no timbre change. Ratings of interval size were strongly influenced by timbre. The six-semitone interval with a congruent timbre change was perceived to be larger than the seven-semitone interval with an incongruent timbre change (interval illusion). Experiment 2 revealed similar effects for musically trained participants. In Experiment 3, participants compared the size of two intervals presented one after the other. Effects of timbre were again observed, including evidence of an interval illusion. Experiment 4 confirmed that timbre manipulations did not distort the perceived pitch of tones. Changes in timbre can expand or contract the perceived size of intervals without distorting individual pitches. We discuss processes underlying interval size perception and their relation to pitch perception mechanisms.

For many years, the Müller-Lyer illusion was studied as a purely "visual" illusion, but like many other optical illusions, the evidence now shows that it also occurs when stimuli are presented tactually. In the present study, we investigated whether the visual perception of the illusion would have any crossmodal consequences for haptic perception. The wings-in and wings-out parts of the Müller-Lyer illusion were placed end-to-end, sharing a central fin. This Brentano version of the illusion was presented visually on a screen in front of the participants, who had to compare the "felt" length of two sticks placed on the back of the screen, one behind either part of the illusion. Our results show that the presentation of the visual illusion modified the felt lengths of the sticks presented directly behind the illusion. In particular, the stick presented on the side of space perceived visually as being shorter (behind the wings-in part of the display) was perceived as longer, and vice versa for the stick mounted behind the space perceived visually as longer (behind the wings-out part of the display). These results highlight the crossmodal consequences of the visual perception of the Müller-Lyer illusion for the haptic perception of line length.

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 of the illusion proposed by Deutsch and Roll (1976) carries three postulates: first, that listeners perceive only the pitch of the tones presented to their dominant ear; second, that this pitch is heard in whichever ear received the higher frequency tone; and third, that this apparent dissociation between what and where mechanisms arises from sequential interactions between the tones. In the present article, we reappraise evidence for the suppression model and demonstrate (1) the incompatibility of the theory with the existing literature on pitch perception, sound localization, and ear dominance and (2) methodological limitations in studies that have claimed to provide support for the suppression model. We conclude by proposing an alternative theory of the octave illusion that is based on established principles of fusion, rather than suppression, between ears.

Two auditory phenomena--stream segregation and illusory continuity through a wide-band noise interruption--were studied to determine whether the same principles of perceptual organization applied to both. A cycle was formed of a repeating alternation of two short bursts of narrow-band noise (NBN), one centered at a high frequency (H) and the other at a low frequency (L), with shorter bursts of wide-band noise (WBN) inserted between successive NBNs (H WBN L WBN H WBN...). In some conditions, listeners could hear a single NBN moving up and down behind the WBN bursts, although there was no NBN present with the WBN. Listeners rated the strength of this illusory continuity. Center frequency separation, rate of onsets, and bandwidth of the NBNs were varied. Increases in values of all three variables decreased illusory continuity. Other listeners rated the stream segregation of the H and L bands when successive NBNs were separated either by WBN bursts (as above) or by silences. The same three acoustic variables were manipulated. Increases in all three variables decreased the perception of a single stream. The similar disruptive effects on illusory continuity and on the one-stream percept in the stream segregation task support the idea that both phenomena depend on a common preliminary process of linking together the parts of a sequence that have similar frequencies.

The effect of spectral motion on the tritone paradox was investigated by pretesting subjects residing in southwestern Ontario, Canada, on the tritone task, presenting them with a continuous ascending or descending chromatic scale created using Shepard tones, and then retesting them on the tritone task. Results indicated a negative-motion aftereffect that affected the orientation of the pitch class circle. Differential effects of perceived pitch height on the lower portion of the pitch class circle and of adaptation on the upper portion of the pitch class circle were found in the pre- and postadaptation data, respectively. The implications of this dissociation are discussed. In addition, since our subjects lived relatively close to the U.S. border, the experimental pretests allowed us to examine the hypothesis that a canonical American pitch template similar to that found among “Californian” subjects (Deutsch, 1991) is propagated by linguistic influences of media such as television and radio (Ragozzine & Deutsch, 1994). A survey of our subjects indicated that overall, the majority of time engaged in listening to the radio and watching television or movies was spent with American sources. Despite this, and despite the fact that subjects had widely varying language and cultural backgrounds, a tight distribution of peak-pitch classes was found that is indicative of a “British” pitch template (Deutsch, 1991) for every subject tested.

When the same syllable is presented repeatedly to a human subject, it undergoes perceptual changes known as verbal transformations. However, the dynamics of such perceptual changes is poorly understood. In the present work we show that the main organization of the perceptual transitions is into pairs. This pairwise coupling is pronounced in the frequency of switching to pair members, but not in their dwell times (the time spent perceiving a given phonemic form before switching to another form). We show that the paircoupled transforms of perception have a faster and more stable dynamic than the nonpaircoupled transforms. We also demonstrate that the pairwise coupling is stronger than would be expected from random arrangement of small numbers of transforms. These characteristic patterns of verbal transforms have been predicted by a mathematical model, first proposed as a model of perceptual alternations of ambiguous visual figures.

To capture faint sounds, the ear uses an active system of amplification. We and our colleagues have put forward the idea that the amplifier comprises a set of ‘self-tuned critical oscillators’: each hair cell contains a force-generating dynamical system which is maintained at the threshold of an oscillatory instability, or Hopf bifurcation. The active response to a pure tone is perfectly suited to the ear’s needs, since it provides frequency selectivity, exquisite sensitivity and wide dynamic range. However, the intrinsic nonlinearity of the mechanism causes tones of different frequency to interfere with one another in the cochlea. In order to provide a framework for understanding how the ear processes the more complex sounds of speech and music, we have examined the response of a critical Hopf oscillator to two tones. Our calculations indicate how the response to one tone is suppressed by the presence of a second tone of similar frequency. They also show how a characteristic spectrum of distortion products is generated. The results are in accord with experimental observations of basilar membrane motion. Given the complexity of the nonlinear response, how does the ear distinguish the frequency components of a sound source? We propose a simple model of pitch extraction based on the timings of neural spikes, and investigate to what extent psychophysical phenomena such as the sensation of dissonance and auditory illusions can be attributed to the physical nature of the peripheral detection apparatus.

In the present experiment, auditory stream organization was investigated in the presence of perceptually restored continuity. It was found that auditory streaming processes tend to yield the same perceptual organization independently of the presence or absence of perceptual restoration. Other observations include the dominance of frequency proximity over trajectory as a perceptual organization principle, and the effect of harmonic enrichment on perceptual grouping.

This study investigated the perceptual effects of either distorting (misarticulating) or deleting word-initial phoneme targets located in two-syllable words. Subjects were instructed to shadow taped prose passages containing the distorted or deleted targets. The subjects typically repeated words containing distorted targets as heard on the tape, and they typically restored words con­ taining deleted targets. That is, the subjects reconstructed the missing acoustic-phonetic infor­ mation even with deletions as large as 137.5 msec. Deleting word-initial consonants apparently had little effect on the word-recognition process during shadowing. The subjects appeared to rely on contextual constraints in lieu of the missing acoustic-phonetic information. The experimental study of fluent speech perception dates back to at least 1900 with the publication of Wil­ liam Chandler Bagley's (190().: 1901) paper, "The Apper­ ception of the Spoken Sentence: A Study in the Psychol­ ogy of Language." In his paper, Bagley examined the role of lexical and semantic constraints in fluent speech per­ ception. Since Bagley's time, much research in fluent speech perception has centered on recognizing words in noisy environments. The majority of the literature has stressed the importance of lexical, semantic, and prosodic con­ straints provided in spoken utterances which help listeners to recognize words in noisy situations. Some ofthis research has dealt with what is now called the "phonemic restoration effect" (Warren, 1970). This auditory illusion, first demonstrated by Bagley, involves a listener's ability to restore missing acoustic informa­ tion due either to a distorted speech signal or to noise. More recently, the role of phonemic restorations in word recognition in fluent speech has been described by Samuel (1981). Although much research has dealt with redundancies in the spoken message, less effort has been given to the study of perception of segments, even though the audi­ tory cues for segment identity present in isolation are often different from those observed in fluent speech (Cole & Jakimik, 1980). Studies involving segmental perception have largely examined the role of consonant distinctive features in word recognition (Cole, 1973; Marslen-Wilson & Welsh, 1978).

A modified Muller-Lyer illusion was used to test whether the adaptation of orientation-specific cells contribute to illusion decrement. Subjects either scanned the illusion configuration (a condition known to produce decrement), fixated one vertex of the illusion configuration, scanned a field of parallel lines set at the same angle from the horizontal as the wings of the illusion configuration (to adapt the orientation-specific receptors), or scanned a field of randomly spaced dots. Over the 5-min test period, those subjects who scanned the illusion configuration between judgments showed significantly more illusion decrement than did any of the other three groups. This suggests that active exploration of the illusion figure, rather than adaptation or fatigue of orientation-specific contour detectors in the cortex, is required for illusion decrement to occur.

Several studies reported that subjects have difficulty in processing a sequence of auditory signals if the sequence alternates between ears: Alternating speech and melodies are recognized poorly. If, however, the ears not receiving this information are "filled" with noise or with a lower constant-frequency tone (drone), recognition improves again. This improvement is due to the fact that the signal is subjectively alternating to a much lesser extent. The present study was an attempt to measure the subjective ambient bandwidth within which the interaural signal moves when a contralateral drone is supplied. It turned out that the signal, although alternating between ears, appeared to arise from the middle of the head. The results were discussed in terms of auditory illusions.

When a speech sound in a sentence is replaced completely by an extraneous sound (such as a cough or tone), the listene restores the missing sound on the bases of both prior and subsequent context. This illusory effect, called phonemic restoration (PhR), causes the physically absent phoneme to seem as real as the speech sounds which are present. The extraneous sound seems to occur along with other phonemes without interfering with their clarity. But if a silent gap (rather than an extraneous sound) replaces the same phoneme, the interruption in the sentence is more readily localized in its true position and PhRs occours less frequently. Quantitative measures were taken both of the incidence of PhRs and of the direction and extent of temporal mislocalizations of interruptions for several related stimuli under a variety of experimental conditions. The results were connected with other auditory illusions and temporal confusions reported in the literature, and suggestions were made concerning mechanisms employed normally for verbal organization.

Description d'un appareil permettant la creation d'illusion auditive interface a un commodore 64

MR. TURNER should have consulted some standard work on experimental psychology before claiming a visual illusion as “new” (NATURE, October 7, p. 180) and advancing an explanation which experiment has shown to be wholly inadequate to account for the retinal after-sensations of movement. The effects are quite independent of movements of the eyes, and as truly “sensory” in character as the after-effects of colour and brightness.

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THE visual illusion described by Mr. Turner and by Prof. Boycott in NATURE of October 7 and 14 was described by me in NATURE of October 18, 1917 (vol. c., p. 126), and commented on by Dr. F. J. Alien and others on pp. 146, 165, 225, and 325 of the same volume. It had also been described in NATURE, vol. Ixx., p. 107, and vol. Ixxviii., pp. 225, 277, and 305. It was also pointed out by me in vol. c., p. 284, that the phenomenon had been fully described by Dr. John Aitken in the Journal of Anatomy and Physiology, vol. xiii., p. 322. The illusion may, perhaps, be best seen by looking through a microscope and slowly rotating the stage; as soon as the rotation is stopped the field appears to be revolving in the opposite direction, and so strong is the illusion that the stage may again be rotated very slowly in the original direction for 10° or 15° and will appear to the eye to be perfectly still. The same phenomenon may be seen when a pianola roll is stopped, the roll appearing to be slowly moving backwards. In some forms of pianola there is, in front of the record, a glass panel on which is a small knob for opening and shutting the panel; if the finger is placed lightly on this knob while the roll appears to be running back, I have the very curious tactual illusion that the knob is also moving upwards, and that it presses more and more against the finger. One or two others, however, with whom I have tried the experiment do not perceive the tactual illusion.

THE visual illusion described by Mr. Turner in NATURE of October 7, p, 180, may be seen very well by looking steadfastly at a long luggage train as in for example, counting the trucks at about 100 yards distance. Immediately after the train has passed, the embankment appears to slide along in the opposite direction.