Search

Audition is accepted as more reliable (thus dominant) than vision when temporal discrimination is required by the task. However, it is not known whether the characteristics of the visual stimulus, for example its familiarity to the perceiver, affect auditory dominance. In this study we manipulated familiarity of the visual stimulus in a well-established multisensory phenomenon, i.e., the sound-induced flash illusion. This illusion occurs when, for example, one brief visual stimulus (e.g., a flash) is presented in close temporal proximity with two brief sounds; participants perceive two flashes instead of one. We found that when the visual stimuli (faces or buildings) were familiar, participants were less susceptible to the illusion than when they were unfamiliar. As the illusion has been ascribed to early cross-sensory interactions between vision and audition, the present work offers behavioural evidence that high level processing of objects' characteristics such as familiarity, affects early temporal multisensory integration. Possible mechanisms underlying the effect of familiarity are discussed.

The human auditory system perceptually restores short deleted segments of speech and other sounds (e.g. tones) when the resulting silent gaps are filled by a potential masking noise. When this phenomenon, known as ‘auditory induction’, occurs, listeners experience the illusion of hearing an ongoing sound continuing through the interrupting noise even though the perceived sound is not physically present. Such illusions suggest that a key function of the auditory system is to allow listeners to perceive complete auditory objects with incomplete acoustic information, as may often be the case in multisource acoustic environments. At present, however, we know little about the possible functions of auditory induction in the sound-mediated behaviours of animals. The present study used two-choice phonotaxis experiments to test the hypothesis that female grey treefrogs, Hyla chrysoscelis, experience the illusory perceptual restoration of discrete pulses in the male advertisement call when pulses are deleted and replaced by a potential masking noise. While added noise restored some attractiveness to calls with missing pulses, there was little evidence to suggest that the frogs actually experienced the illusion of perceiving the missing pulses. Instead, the added noise appeared to function as an acoustic appendage that made some calls more attractive than others as a result of sensory biases, the expression of which depended on the temporal order and acoustic structure of the added appendages.

It is argued that speech perception, just like visual perception, relies on a good match between memorized experience and current sensation: when sensation meshes with expectations, listeners believe they perceive ‘real’ linguistic objects in spite of possibly severe variation and degradation in the acoustic signal. Reviews of the acoustic and perceptual correlates of the features [nasal] and [voice] in various speech styles illustrate how multiple perceptual cues to a simple phonological distinction may be dispersed across syllables, and how absence of one or several such cues may be compensated by the presence of others, or by recovery processes that rely on listeners’ knowledge and expectations. Visual illusions are discussed which have apparent parallels with auditory illusions and with well-known aspects of speech perception. These include particular types of physical structure (e.g. abrupt changes, edges), enhancement of properties of a given object by juxtaposed information which either changes the percept of those properties, or else provides a context that changes the percept of what the object is, and influences of familiarity and probability which can be profound enough to fly in the face of contrary sensory evidence. These data are used to support the hypothesis that perceived linguistic units, including distinctive features, are ephemeral (and illusory) ‘auditory objects’, which are created by the listening brain using domain-general processes that underpin meaningful behaviour.

Objective: To define brain activity corresponding to an auditory illusion of 3 and 6 Hz binaural beats in 250 Hz or 1000 Hz base frequencies, and compare it to the sound onset response. Methods: Event-Related Potentials (ERPs) were recorded in response to unmodulated tones of 250 or 1000 Hz to one ear and 3 or 6 Hz higher to the other, creating an illusion of amplitude modulations (beats) of 3 Hz and 6 Hz, in base frequencies of 250 Hz and 1000 Hz. Tones were 2000 ms in duration and presented with approximately 1 s intervals. Latency, amplitude and source current density estimates of ERP components to tone onset and subsequent beats-evoked oscillations were determined and compared across beat frequencies with both base frequencies. Results: All stimuli evoked tone-onset P50, N100 and P200 components followed by oscillations corresponding to the beat frequency, and a subsequent tone-offset complex. Beats-evoked oscillations were higher in amplitude with the low base frequency and to the low beat frequency. Sources of the beats-evoked oscillations across all stimulus conditions located mostly to left lateral and inferior temporal lobe areas in all stimulus conditions. Onset-evoked components were not different across stimulus conditions; P50 had significantly different sources than the beats-evoked oscillations; and N100 and P200 sources located to the same temporal lobe regions as beats-evoked oscillations, but were bilateral and also included frontal and parietal contributions. Conclusions: Neural activity with slightly different volley frequencies from left and right ear converges and interacts in the central auditory brainstem pathways to generate beats of neural activity to modulate activities in the left temporal lobe, giving rise to the illusion of binaural beats. Cortical potentials recorded to binaural beats are distinct from onset responses. Significance: Brain activity corresponding to an auditory illusion of low frequency beats can be recorded from the scalp. © 2009 International Federation of Clinical Neurophysiology.

Shepard's tones are a typical example for auditory illusion. They consist in a series of computer generated tones, which prohibit relative pitch discrimination. As a result, when repetitively played in sequence, the illusion of an ever-ascending scale is evoked. In order to investigate this aural phenomenon, fMRI time series were acquired during presentation of a conventional block-designed paradigm as well as during continuous presentation of Shepard's tones. With respect to the different setups of the two experiments, two fundamentally different methods were applied in order to conduct data analysis. Common Statistical Parameter Mapping served to evaluate the time series obtained with the block-designed paradigm. For the continuous experiment, a novel wavelet-based multifractal analysis was used, recently proposed as a classification tool for fMRI time series. This approach applies the wavelet transform to extract multifractal spectra from time-signals. For reasons of quantification, we introduced an ameliorated method for visual inspection of the multifractal properties. The results proved existence of characteristic neural responses to continuously presented Shepard's tones. Interestingly, the same was not restricted to the auditory cortex, but also involved areas of the visual cortex. Related impact on the imaged cognitive areas, primary motor cortex, and primary sensory cortex could not be observed. We further provide evidence that pitch misjudgment does not occur in temporal concurrence with the repetition of the whole scale, but according to whether the main perceived frequency is located in the sensitive range of auditory perception or not. We remark that this is the first time, continuously stimulated brain areas could be detected by means of fMRI.

This article reports the first study of the glissando illusion, which was created and published as a sound demonstration by Deutsch [Deutsch, D. (1995). Musical illusions and paradoxes. La Jolla: Philomel Records (compact disc)]. To experience the illusion, each subject was seated in front of two stereophonically separated loudspeakers, with one to his left and the other to his right. A sound pattern was presented that consisted of a synthesized oboe tone of constant pitch, together with a sine wave whose pitch repeatedly glided up and down (the glissando). These two components alternated continuously between the loudspeakers such that when the oboe tone emanated from the loudspeaker on the left, the glissando emanated from the loudspeaker on the right; and vice versa. The oboe tone was perceived correctly as switching between loudspeakers; however, the segments of the glissando appeared to be joined together seamlessly, such that a single, continuous tone was heard, which appeared to be moving slowly around in space in accordance with its pitch motion. Right-handers (n = 22) tended strongly to hear the glissando move between left and right, and also between low and high in space, as its pitch moved between low and high. More specifically, it was frequently heard as tracing an elliptical path aligned diagonally between a position low and to the left when its pitch was lowest, and high and to the right when its pitch was highest. Non-right-handers (n = 42) perceived the illusion in statistically different ways. The handedness correlates and other implications of the glissando illusion are discussed. © 2007 Elsevier Ltd. All rights reserved.

Question ”McGurk effect” is known as an auditory illusion caused by interference from unmatched visual inputs. For example, a combination of auditory/Pa/ and visual/Ka/ results in the perception of a third syllable of/Ta/. Recent neuroimaging studies proposed that left posterior superior temporal sulcus (pSTS), a hub region of audiovisual integration, is concerned with McGurk effect. However, the mechanisms still remain under debate. Methods 27 right-handed healthy volunteers received audiovisual incongruent (auditory/Ba//Pa/ and visual/Ga//Ka/) and congruent (both/Ba//Pa/) perceptual tasks, and then they were asked the syllables listened to. We investigated activated brain regions in event-related functional magnetic resonance imaging (fMRI) study. In addition, we applied single-pulse transcranial magnetic stimulation (TMS) over the lip or foot area of the primary motor cortex (M1) in an event-related design and we measured McGurk susceptibility. Results Behaviorally, audiovisual incongruent trials resulted in higher illusion susceptibility and longer reaction time than congruent trials. FMRI study revealed brain activations in audiovisual areas, dorsal premotor cortex (dPMC) and inferior frontal gyrus (IFG), bilaterally in both audiovisual stimuli. Activations in dPMC and IFG were more prominent in incongruent task, whereas stronger activations of the pSTS in congruent task. Left IFG activation correlated negatively with McGurk susceptibility. Psychophysiological interaction analysis demonstrated increased effective connectivity between the left IFG and M1 lip area in incongruent task. Event-related TMS over M1 lip area showed significant reduction of McGurk susceptibility when compared with TMS over M1 foot area or the control condition (no TMS). Conclusions We showed that the motor system contributes to recognition of audiovisual inputs and it is more active in incongruent condition, while the pSTS is more active in congruent condition. The left IFG-M1 network plays some roles in detecting and resolving multisensory incompatibility to reduce illusion.

The Zwicker tone (ZT) is an auditory after-image, i.e. a tonal sensation that occurs following the presentation of notched noise. In the present study, the hypothesis that neural lateral inhibition is involved in the generation of this auditory illusion was investigated in humans through differences in perceptual detection thresholds measured following broadband noise, notched noise, and low-pass noise stimulation. The detection thresholds were measured using probe tones at several frequencies, within as well as outside the suppressed frequency range of the notched noise, and below as well as above the corner frequency of the low-pass noise. Thresholds measured after broadband noise using a sequence of four 130-ms probe tones (with a 130-ms inter-burst interval) proved to be significantly smaller that those measured using the same probe tones after notched noise at frequencies falling within the notch, but larger for frequencies on the outer edges of the noise. Thresholds measured following low-pass noise using the same sequence of probe tones were found to be smaller at frequencies slightly above the corner, but larger at lower, neighboring frequencies. This pattern of results is consistent with the hypothesis that the changes in auditory sensitivity induced by stimuli containing sharp spectral contrasts reflect lateral inhibition processes in the auditory system. The potential implications of these findings for the understanding of the mechanisms underlying the generation of auditory illusions like the ZT or tinnitus are discussed.

Seventeen schizophrenic patients who had all experienced auditory hallucinations were compared with 14 subjects of a reference group on a test of contralateral induction. Contralateral induction means that a sound is illusively heard as coming from a location where it belongs according to its spectral content. The phenomenon is connected with a simultaneous relative elimination of masking. The schizophrenic subjects deviated from the reference group in several aspects. Some of them did not hear the sound being induced to the contralateral side, which it was for all reference subjects. Another subgroup of the schizophrenics noticed the induction unusually early with a prolonged experience of it, and finally some of them experienced the induction now and then. The aberrations were interpreted as rigidity of adaptation on the one hand and as effects of an enhanced sensitivity on the other. Discontinuity, meaning that the fluency in mental processing is broken, was interpreted to cause the ratings of the third group of schizophrenics in this sample, who heard the contralateral induction now and then. These phenomena are clearly reminiscent of descriptions in research reports, and witnessed by clinical experience of the schizophrenic disturbance. The results represent another example of discontinuous neurophysiological functions between neural systems and between individuals suffering from schizophrenia.

Here the problem of the verification of new illusions is addressed. Subtle perceptual illusory experiences can be hard to recognize, meaning that it can be difficult or impossible for an introspecting psychologist to convey a new illusion or verify that other people experience a new illusion without polluting other people's experience by introducing biasing expectations through the very act of describing what the illusory experience might be like. The proposed solution is to offer subjects an array of descriptions of faux illusions that are known to be unexperienceable, along with the new illusion, in order to determine whether naive subjects are uniquely more likely to report an illusory experience for the hypothetical new illusion than for the faux illusions.

Right auditory cortex dysfunction during musical hallucinations occurred in an 88-year-old woman, who was otherwise cognitively intact. We assessed this phenomenon with a combination of neuromagnetic and cerebral blood-flow measurements.

In recent years, cognitive neuroscience has been making great efforts to home in on the difference between the physical stimulus and the perceived sensation, hence the attempts to find neural correlates of what we actually perceive. In auditory illusions, the pitch of a sound – its subjective highness or lowness – may not be the same as its physical frequency. In the missing frequency (MF) illusion, for example, people can hear frequencies not present in physical sound waves. Using MF stimuli and magnetoencephalography (MEG), Patel and Balaban recently showed that there is a correlation between the temporal pattern of brain activation in the right cerebral hemisphere and the subjectively perceived pitch [Nature Neurosci. (2001) 4, 839–844]. Using the fact that people differ in their susceptibility to the MF illusion, Patel and Balaban divided their subjects into those who perceived pitch change in the same direction as frequency change, and those who perceived it in the opposite direction. Comparing MEG scans from the two groups of subjects, they found that, although many areas of the brain respond to the stimulus of a frequency change, only areas in the right hemisphere code for change of subjective pitch. MW

Twenty-seven right- and fourteen left-handed subjects with varying amounts of musical training listened to dichotic octave patterns. Each pattern consisted of twenty 250-msec. tones which oscillated from 400 to 800 Hz. Patterns were combined in such a way that while one ear received a 400 Hz tone, an 800 Hz tone was simultaneously present in the opposite ear. Reported perception of these patterns was significantly related to the handedness of the subjects. In addition, responses of subjects with musical training differed significantly from those of untrained subjects. An hypothesis is suggested that musical training serves to establish a sharper psychophysical criterion for judging unfamiliar sounds. Further research should be directed toward understanding the relationship between the octave illusion and cerebral dominance.

The precedence effect is an auditory illusion produced by playing a sound through two loudspeakers with one loudspeaker output delayed relative to the other. Adults report hearing a single sound located at the leading loudspeaker. Research with animals indicates that the auditory cortex is essential for perceiving the precedence effect. In a previous study newborns did not reliably turn their heads toward precedence-effect sounds produced by a 7 msec delay interval, but did turn toward the same sounds presented through a single loudspeaker. To determine if variation in temporal delays would affect head turning, 24 alert newborns were presented with three precedence-effect stimuli produced by a 5, 20, and 50 msec delay interval. The same sound presented from a single loudspeaker served as the control stimulus. In addition to head orientation to sound, heart rate was measured to investigate the relationship between cardiac and behavioral orienting. Infants correctly turned toward sound from the single loudspeaker but did not turn toward any of the precedence-effect stimuli. Cardiac deceleration was obtained only on trials unaccompanied by head turns. When head turns occurred, there was no reliable cardiac response.

Phonemic restoration is a powerful auditory illusion in which listeners hear a part of a word that has in fact been replaced by another sound. Two experiments explore whether the strength of the illusion is affected by whether a single lexical item could be restored. In Experiment 1, more perceptual restoration was found for stimuli that were multiply restorable (e.g., “_egion” → “legion” or “region”) than for lexically unique ones (e.g., “_esion” → “lesion”). In Experiment 2, lexical uniqueness was examined as a function of time: Words become lexically unique when enough has been heard to eliminate all alternatives. This manipulation also affected the strength of the illusion. The results complement those of other techniques in supporting an active role for lexical representations in the perception of speech.

The auditory perception of distance may be altered by systematically transforming the time and intensity ratios of the auditory cues at a subject's ears. Two auditory ‘illusions’ of depth, opposite in sign, were generated, by attenuating in one case and masking with white noise in the other, the signal in one ear from an ‘auditory pendulum’. The change in perceived depth of the acoustic pendulum with attenuation of one ear was analogous to the Pulfrich phenomenon in vision. These auditory experiments suggested two additional ways of generating visual Pulfrich effects that were then demonstrated.