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Background Interesting data and theories have emerged regarding auditory hallucinations (AHs) in patients with schizophrenia. The possibility that these patients may have changes in the anatomy of the auditory cortex and/or subcortical structures of the central auditory nervous system and present with deficits on audiological tests is important information to the audiology community. However, it seems clear that, in general, audiologists are not sufficiently aware of these findings. Purpose There are two main purposes of this article: (1) to educate audiologists about AHs related to schizophrenia and related issues, and (2) to encourage audiologists and hearing scientists to become involved in the evaluation and research of AHs. This fascinating disorder is one in which audiologists/hearing scientists are well suited to make a significant contribution. Research Design A review and synthesis of the literature was conducted. Relevant literature was identified through PubMed, Google Scholar, as well as independent book chapters and article searches. Keywords driving the searches were AHs, auditory illusions, verbal and musical hallucinations, schizophrenia, and central auditory disorders. Given the currency of the topic, the information collected was primarily between 1990 and 2020. Study Sample The review is organized around categorization, prevalence, models, mechanisms, anatomy, pathophysiology, and audiological correlates related to AHs. Data Collection and Analysis Searches were conducted using well-known search engines and manual searches by each author. This information on AHs was then analyzed collectively by the authors for useful background and relevance, as well as important for the field of audiology. Results Several anatomical, physiological, and functional imaging studies have shown compromise of the auditory cortex in those with schizophrenia and AHs. Potentially related to this, are studies that demonstrated sub-par performance on behavioral audiologic measures for this unique clinical population. These findings align well with the kind of hearing disorder for which audiologists are well-trained to make significant contributions. Conclusion Neurobiological and audiological evidence is accumulating on patients with schizophrenia and AH potentially rendering it as both an auditory and psychiatric disorder. Audiologists should consider expanding their horizon and playing a role in the clinical investigation of this disorder.

OBJECTIVEExperiential phenomena (EP), such as illusions and complex hallucinations, are vivid experiences created in one’s mind. They can occur spontaneously as epileptic auras or can be elicited by electrical brain stimulation (EBS) in patients undergoing presurgical evaluation for drug-resistant epilepsy. Previous work suggests that EP arise from activation of different nodes within interconnected neural networks mainly in the temporal lobes. Yet, the anatomical extent of these neural networks has not been described and the question of lateralization of EP has not been fully addressed. To this end, an extended number of brain regions in which electrical stimulation elicited EP were studied to test whether there is a lateralization propensity to EP phenomena.METHODSA total of 19 drug-resistant focal epilepsy patients who underwent EBS as part of invasive presurgical evaluation and who experienced EP during the stimulation were included. Spatial dispersion of visual and auditory illusions and complex hallucinations in each hemisphere was determined by calculation of Euclidean distances between electrodes and their centroid in common space, based on (x, y, z) Cartesian coordinates of electrode locations.RESULTSIn total, 5857 stimulation epochs were analyzed; 917 stimulations elicited responses, out of which 130 elicited EP. Complex visual hallucinations were found to be widely dispersed in the right hemisphere, while they were tightly clustered in the occipital lobe of the left hemisphere. Visual illusions were elicited mostly in the occipital lobes bilaterally. Auditory illusions and hallucinations were evoked symmetrically in the temporal lobes.CONCLUSIONSThese findings suggest that complex visual hallucinations arise from wider spread in the right compared to the left hemisphere, possibly mirroring the asymmetry in the white matter organization of the two hemispheres. These results offer some insights into lateralized differences in functional organization and connectivity that may be important for functional mapping and planning of surgical resections in patients with epilepsy.

Mating signals have evolved to attract target receivers, even to the point of exploiting receivers through perceptual manipulation. Signals, however, can also expose signalers to nontarget receivers, including predators and parasites, and thus have also evolved to decrease enemy attraction. Here we show that male tree frogs (Smilisca sila) reduce their attractiveness to eavesdropping enemies (bats and midges) by overlapping their calls at near-perfect synchrony with the calls of neighboring conspecifics. By producing calls that closely follow those of other males, synchronizing S. sila take advantage of an auditory illusion where enemies are more attracted to the leading call. Female S. sila, however, are less susceptible to this illusion. Thus, synchronization among signaling males can result in acoustic crypsis from predators without affecting female attraction. Given the widespread use of conspicuous mating signals and eavesdropping enemies, perceptual exploitation of eavesdroppers is likely a common driver of signal evolution.

Several studies have demonstrated the neural correlates of chronic tinnitus. However, we still do not understand what happens in the acute phase. Past studies have established Zwicker tone (ZT) illusions as a good human model for acute tinnitus. ZT illusions are perceived following the presentation of a notched noise stimulus, that is, broadband noise with a narrow band‐stop filter (notch). In the current study, we compared the neural correlates of the reliable perception of a ZT illusion to that which is not. We observed changes in evoked and total theta power in wide‐spread regions of the brain particularly in the temporal‐parietal junction, pregenual anterior cingulate cortex/ventromedial prefrontal cortex (pgACC/vmPFC), parahippocampus during perception of the ZT illusion. Furthermore, we observe that increased theta power significantly predicts a gradual positive change in the intensity of the ZT illusion. Such changes may suggest a malfunction of the sensory gating system that enables habituation to redundant stimuli and suppresses hyperactivity. It could also suggest a successful retrieval of the memory of the missing frequencies, resulting in their conscious perception indicating the role of higher‐order processing in the mechanism of action of ZT illusions. To establish a more concrete relationship between ZT illusion and chronic tinnitus, future longitudinal studies following up a much larger sample of participants who reliably perceive a ZT illusion to see if they develop tinnitus at a later stage is essential. This could inform us if the ZT illusion may be a precursor to chronic tinnitus.

It is well established that the human auditory system is capable of filling in missing pieces of a speech stream through a process known as phonemic restoration, yet a neural understanding of this phenomenon has been limited by the lack of a suitable animal model. Songbirds, and especially zebra finches, have proven to be a fruitful model for speech perception and production, making them a promising model for studying restoration of complex vocalizations. In this work, I established through behavioral testing that zebra finches experience this illusion and then recorded single-unit neural data to characterize the neural representation of restored birdsong. Using a decoding method, I was able to identify neural responses consistent with restoration. These responses were widely distributed through the avian auditory cortex but especially strongly represented in the deep auditory pathway. I also found that the evidence for restoration grew stronger over the course of the missing syllable, suggesting the involvement of an internal predictive model that suppresses the incoming auditory signal.

There has been burgeoning interest in studying hallucinations in psychosis occurring across multiple sensory modalities. The current study aimed to characterize the auditory hallucination and delusion profiles in patients with auditory hallucinations only versus those with multisensory hallucinations. Participants with psychosis were partitioned into groups with voices only (AVH; n = 50) versus voices plus hallucinations in at least one other sensory modality (AVH+; n = 50), based on their responses on the Scale for the Assessment of Positive Symptoms (SAPS). Basic demographic and clinical information was collected, and the Questionnaire for Psychotic Experiences (QPE) was used to assess psychosis phenomenology. Relative to the AVH group, greater compliance to perceived commands, auditory illusions, and sensed presences was significantly elevated in the AVH+ group. The latter group also had greater levels of delusion-related distress and functional impairment and was more likely to endorse delusions of reference and misidentification. This preliminary study uncovered important phenomenological differences in those with multisensory hallucinations. Future hallucination research extending beyond the auditory modality is needed.

Music without audience is difficult to imagine. Here we try to analyze how our hearing mechanism works, though there are many things we do not yet understand and which remain hidden in a huge black box. We discuss absolute and relative pitches, as well as auditory illusions.

It is pointed out that beyond reproducing the physically correct sound pressure at the eardrums, more effects play a significant role in the quality of the auditory illusion. In some cases, these can dominate perception and even overcome physical deviations. Perceptual effects like the room-divergence effect, additional visual influences, personalization, pose and position tracking as well as adaptation processes are discussed. These effects are described individually, and the interconnections between them are highlighted. With the results from experiments performed by the authors, the perceptual effects can be quantified. Furthermore, concepts are proposed to optimize reproduction systems with regard to those effects. One example could be a system that adapts to varying listening situations as well as individual listening habits, experience and preference.

Perception of sound fields reproduced by loudspeaker arrays which are driven by spatial-audio technologies, such as Wave-Field Synthesis or Higher-Order Ambisonics, is examined in the light of “Spatial Auditory Illusions”. The spatial-audio technologies are based on illusions as to which real sound-sources vanish perceptually in favor of virtual sources. Furthermore, spatial-audio technologies are able to synthesize sound fields which are very similar to sound fields as created by real sources. In this chapter, these illusions are first explored as a function of the acoustic (physical) properties of the synthesized sound fields. Then, the perceptual dimensions are reviewed of what is actually heard when being exposed to these synthesized sound fields.

Visual Abstract, Binaural beating is a perceptual auditory illusion occurring when presenting two neighboring frequencies to each ear separately. Several controversial claims have been attributed to binaural beats regarding their ability to entrain human brain activity and mood, in both the scientific literature and the marketing realm. Here, we sought to address those questions in a robust fashion using a single-blind, active-controlled protocol. To do so, we compared the effects of binaural beats with a control beat stimulation (monaural beats, known to entrain brain activity but not mood) across four distinct levels in the human auditory pathway: subcortical and cortical entrainment, scalp-level functional connectivity and self-reports. Both stimuli elicited standard subcortical responses at the pure tone frequencies of the stimulus [i.e., frequency following response (FFR)], and entrained the cortex at the beat frequency [i.e., auditory steady state response (ASSR)]. Furthermore, functional connectivity patterns were modulated differentially by both kinds of stimuli, with binaural beats being the only one eliciting cross-frequency activity. Despite this, we did not find any mood modulation related to our experimental manipulation. Our results provide evidence that binaural beats elicit cross frequency connectivity patterns, but weakly entrain the cortex when compared with monaural beat stimuli. Whether binaural beats have an impact on cognitive performance or other mood measurements remains to be seen and can be further investigated within the proposed methodological framework.

We recently showed that auditory illusions of self-motion can be induced in the absence of physically accurate spatial cues (Mursic et al., 2017). The current study was aimed at identifying which features of this auditory stimulus (the Shepard–Risset glissando) were responsible for this metaphorical auditory vection, as well as confirming anecdotal reports of motion sickness for this stimulus. Five different types of auditory stimuli were presented to 31 blindfolded, stationary participants through a loudspeaker array: (1) a descending Shepard–Risset glissando; (2) a descending discrete Shepard scale; (3) a descending sweep signal; (4) a phase-scrambled version of (1) (auditory control type 1); and (5) white noise (auditory control type 2). We found that the auditory vection induced by the Shepard–Risset glissando was stronger than both types of auditory control, and the discrete Shepard scale stimulus. However, vection strength was not found to differ between the Shepard–Risset glissando and the sweep signal. This suggests that the continuous, gliding structure of both these auditory stimuli was integral to the induction of vection. Consistent with anecdotal reports that the Shepard–Risset glissando is also capable of generating motion sickness (as measured by the Fast Motion Sickness Scale and the Simulator Sickness Questionnaire), the likelihood and severity of sickness for these stimuli was found to increase with the strength of the auditory vection.

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link The solitaire illusion is an illusion of numerosity proposed by Frith and Frith. In the original version, an apparent number of elements was determined by the spatial arrangement of two kinds of elements (black and white marbles). In our study, an auditory version of the solitaire illusion was demonstrated. Participants were asked to judge if they perceived more drum or piano sounds. When half of the piano tones were perceived as lower in pitch than a drum sound and the other half higher, piano tones appeared to be arranged in small units, leading to numerosity underestimation. Conversely, when all piano tones were perceived to be higher in pitch than the drum sounds, they appeared to be arranged in a single large unit, leading to numerosity overestimation. Comparable to the visual version of the solitaire illusion, the clustering seems to be determined by Gestalt principles. In our auditory version, a clear reversal of the illusion (numerosity overestimation or underestimation) was observed when piano tones appeared to be arranged in a single large cluster or in several small clusters, respectively.

Palinacousis is an auditory illusion rarely reported in cases of temporal lobe dysfunction. After reviewing the literature and comparing our clinical experience, we believe that palinacousis can occur as an aura, a simple partial seizure, a complex partial seizure, and/or a postictal event. Palinacousis maybe more common than recognized in patients with receptive aphasias or diffuse cerebral dysfunction, whose language deficits preclude adequate description. We report the case of a 71 years old man with the previously diagnosis of an infarction of left middle cerebral artery and valvular heart disease who presented with the symptoms of palinacousis. He was not diagnosed psychotic diseases. An electroencephalography showed normal wave. He was diagnosed as temporal lobe epilepsy with palinacousis due to post-stroke. Palinacousis was completely reversed after treatment with antiepileptic drug. We report that palinacousis as an epileptic phenomenon can help localized potential lesions and can improve patient care.

The speech-to-song illusion is a type of auditory illusion that the repetition of a part of a sentence would change people’s perception tendency from speech-like to song-like. The study aims to examine how pace, emotion, and language tonality affect people’s experience of the speech-to-song illusion. It uses a between-subject (Pace: fast, normal, vs. slow) and within-subject (Emotion: positive, negative, vs. neutral; language tonality: tonal language vs. non-tonal language) design. Sixty Hong Kong college students were randomly assigned to one of the three conditions characterized by pace. They listened to 12 audio stimuli, each with repetitions of a short excerpt, and rated their subjective perception of the presented phrase, whether it sounded like a speech or a song, on a five-point Likert-scale. Paired-sample t-tests and repeated measures ANOVAs were used to analyze the data. The findings reveal that a faster speech pace could strengthen the tendency of the speech-to-song illusion. Neither emotion nor language tonality show a statistically significant influence on the speech-to-song illusion. This study suggests that the perception of sound should be in a continuum and facilitates the understanding of song production in which speech can turn into music by having repetitive phrases and to be played in a relatively fast pace.

Aim The aim of this study was to investigate the types and prevalence of epileptic auditory auras (EAA) in a large population with epilepsy based on a clinical analysis, to analyze the relationship between auditory auras and the hemispheric lateralization/localization of the epileptogenic zone, and to determine whether there is a reliable EAA that could be used for the identification of the localization and lateralization of the epileptogenic zone. Methods The retrospective study included 1050 patients with a diagnosis of epilepsy, including 854 (81.33%) patients with focal epilepsy and 196 (18.67%) with generalized epilepsy. Medical records of 72 patients with auditory auras were singled out, and 63 of them were included in the study. The auditory auras were classified based on their clinical characteristics, and an analysis was performed to examine the relation of the type of auditory auras with the hemispheric lateralization/localization of the epileptogenic zone. Additionally, further analyses were performed to investigate whether there can be a reliable EAA that could be used for the identification of the localization and lateralization of the epileptogenic zone. Results Of the 1050 patients with a diagnosis of epilepsy, 63 cases of EAA were included in the study. The prevalence of EAA was 6% in the population with generalized epilepsy and 7.38% in the patients with focal epilepsy. Of the 63 patients, 58 (92.06%) were right-hand-dominant, and 5 (7.94%) were left-hand-dominant. The epileptogenic zone was mostly localized to the temporal lobe (n = 56; 88.89%). In all the 12 patients that had isolated auditory illusion or auditory illusion + elementary or complex auditory hallucinations, the epileptogenic zone was lateralized to the dominant hemisphere and even localized to the temporal lobe of the dominant hemisphere. Significance The prevalence of EAA in the population with generalized epilepsy can be found higher than expected if a detailed evaluation of the population with generalized epilepsy can be performed, as in specific patient groups. Our results indicated that the epileptogenic zone was lateralized to the dominant hemisphere in all the patients with isolated auditory illusion or auditory illusion + elementary or complex auditory hallucinations, which suggests that auditory illusion can be a reliable tool in the determination of the lateralization and even localization of the epileptogenic zone.

International audience; An auditory illusion caught the world’s attention recently. For the same noisy speech utterance, different people reported hearing either ‘Laurel’ or ‘Yanny’. The dichotomy highlights how perceptions are inferences from inherently ambiguous sensory information, even though ambiguity is often unnoticed.

In music theory, the triton is defined as a musical interval composed of three adjacent whole tones(or six semitones), which generates a harmonic and melodic dissonance. The triton paradox is an auditory illusion which is heard as ascending by some people and as descending by others. In this paper we examine an emerging non-static biometric technique that aims to identify users based on analyzing uniqueness and consistency through the user experiences. We also propose some authentication schemes which provides protection against key logging, shoulder surfing, and brute force attacks.

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.

Early in the twentieth century, the Gestalt psychologists outlined principles governing the ability of the human visual system to construct integrated percepts of objects in visual scenes. By the close of the twentieth century, ample evidence suggested that the human auditory system follows similar principles of perceptual organization. Several Gestalt principles of grouping—proximity, similarity, common fate, good continuation, and familiarity, govern our ability to decompose complex mixtures of sounds into percepts of auditory objects in acoustic scenes. Auditory objects are perceptual groupings of sounds generated by the same source that are present at different times and in different parts of the frequency spectrum. The ability to form auditory objects likely plays an important role in allowing animals to navigate human-altered soundscapes. This chapter reviews studies of insects, fish, frogs, birds, and nonhuman mammals in which experimenters manipulated potential grouping cues and measured performance on behavioral tasks designed to reveal the animal’s perception of auditory objects. These studies employed techniques ranging from measuring natural behaviors in response to communication signals to operant conditioning of responses to artificial sounds such as pure tones. The totality of the studies reviewed here unequivocally reveals that nonhuman animals not only form auditory objects but that they also follow the Gestalt principles of grouping. These principles and their underlying mechanisms allow animals to perceptually organize the often noisy and complex acoustic environments in which they live.

In spatial perception, visual information has higher acuity than auditory information and we often misperceive sound-source locations when spatially disparate visual stimuli are presented simultaneously. Ventriloquists make good use of this auditory illusion. In this study, we investigated neural substrates of the ventriloquism effect to understand the neural mechanism of multimodal integration. This study was performed in 2 steps. First, we investigated how sound locations were represented in the auditory cortex. Secondly, we investigated how simultaneous presentation of spatially disparate visual stimuli affects neural processing of sound locations. Based on the population rate code hypothesis that assumes monotonic sensitivity to sound azimuth across populations of broadly tuned neurons, we expected a monotonic increase of blood oxygenation level-dependent (BOLD) signals for more contralateral sounds. Consistent with this hypothesis, we found that BOLD signals in the posterior superior temporal gyrus increased monotonically as a function of sound azimuth. We also observed attenuation of the monotonic azimuthal sensitivity by spatially disparate visual stimuli. The alteration of the neural pattern was considered to reflect the neural mechanism of the ventriloquism effect. Our findings indicate that conflicting audiovisual spatial information of an event is associated with an attenuation of neural processing of auditory spatial localization.

PURPOSE Palinacousis is an auditory illusion of sound persisting or repeating after the cessation of an auditory stimulation. Up until now, approximately 32 cases have been reported. The purpose of this study is to describe an additional seven cases of palinacousis and review our understanding of audition and palinacousis. METHODS Patients seen in the epilepsy clinic or admitted to the Epilepsy Monitoring Unit (EMU) at The Mount Sinai Hospital who experienced palinacousis were included. In all these patients, an EEG and MRI were performed at some point during their clinical course. RESULTS In one case, palinacousis occurred with stimulation of the superior temporal gyrus during brain mapping after a spoken word as well as after the thought of a word. Two people experienced palinacousis during a seizure captured on video EEG. The remaining four cases had palinacousis in the peri- or post-ictal period. CONCLUSIONS We propose that palinacousis may be coming from the superior temporal gyrus secondary to seizure activity, either onset or spread, or dysfunction of the area in a postictal state. The existence of palinacousis in these pathologic states can help us to understand how we process auditory information.

Human listeners place greater weight on the beginning of a sound compared to the middle or end when determining sound location, creating an auditory illusion known as the Franssen effect. Here, we exploited that effect to test whether human auditory cortex (AC) represents the physical vs. perceived spatial features of a sound. We used functional magnetic resonance imaging (fMRI) to measure AC responses to sounds that varied in perceived location due to interaural level differences (ILD) applied to sound onsets or to the full sound duration. Analysis of hemodynamic responses in AC revealed sensitivity to ILD in both full-cue (veridical) and onset-only (illusory) lateralized stimuli. Classification analysis revealed regional differences in the sensitivity to onset-only ILDs, where better classification was observed in posterior compared to primary AC. That is, restricting the ILD to sound onset-which alters the physical but not the perceptual nature of the spatial cue-did not eliminate cortical sensitivity to that cue. These results suggest that perceptual representations of auditory space emerge or are refined in higher-order AC regions, supporting the stable perception of auditory space in noisy or reverberant environments and forming the basis of illusions such as the Franssen effect.

Transcutaneous, electrical stimulation with electrodes placed on the mastoid processes represents a specific way to elicit vestibular reflexes in humans without active or passive subject movements, for which the term galvanic vestibular stimulation was coined. It has been suggested that galvanic vestibular stimulation mainly affects the vestibular periphery, but whether vestibular hair cells, vestibular afferents, or a combination of both are excited, is still a matter of debate. Galvanic vestibular stimulation has been in use since the late 18th century, but despite the long-known and well-documented effects on the vestibular system, reports of the effect of electrical stimulation on the adjacent cochlea or the ascending auditory pathway are surprisingly sparse. The present study examines the effect of transcutaneous, electrical stimulation of the human auditory periphery employing evoked and spontaneous otoacoustic emissions and several psychoacoustic measures. In particular, level growth functions of distortion product otoacoustic emissions were recorded during electrical stimulation with alternating currents (2 Hz, 1–4 mA in 1 mA-steps). In addition, the level and frequency of spontaneous otoacoustic emissions were followed before, during, and after electrical stimulation (2 Hz, 1–4 mA). To explore the effect of electrical stimulation on the retrocochlear level (i.e. on the ascending auditory pathway beyond the cochlea), psychoacoustic experiments were carried out. Specifically, participants indicated whether electrical stimulation (4 Hz, 2 and 3 mA) induced amplitude modulations of the perception of a pure tone, and of auditory illusions after presentation of either an intense, low-frequency sound (Bounce tinnitus) or a faint band-stop noise (Zwicker tone). These three psychoacoustic measures revealed significant perceived amplitude modulations during electrical stimulation in the majority of participants. However, no significant changes of evoked and spontaneous otoacoustic emissions could be detected during electrical stimulation relative to recordings without electrical stimulation. The present findings show that cochlear function, as assessed with spontaneous and evoked otoacoustic emissions, is not affected by transcutaneous electrical stimulation, at the currents used in this study. Psychoacoustic measures like pure tone perception, but also auditory illusions, are affected by electrical stimulation. This indicates that activity of the retrocochlear ascending auditory pathway is modulated during transcutaneous electrical stimulation.

Can what we imagine hearing change what we see? Whether imagined sensory stimuli are integrated with external sensory stimuli to shape our perception of the world has only recently begun to come under scrutiny. Here, we made use of the cross-bounce illusion in which an auditory stimulus presented at the moment two passing objects meet promotes the perception that the objects bounce off rather than cross by one another to examine whether the content of imagined sound changes visual motion perception in a manner that is consistent with multisensory integration. The results from this study revealed that auditory imagery of a sound with acoustic properties typical of a collision (i.e., damped sound) promoted the bounce-percept, but auditory imagery of the same sound played backwards (i.e., ramped sound) did not. Moreover, the vividness of the participants’ auditory imagery predicted the strength of this imagery-induced illusion. In a separate experiment, we ruled out the possibility that changes in attention (i.e., sensitivity index d′) or response bias (response bias index c) were sufficient to explain this effect. Together, these findings suggest that this imagery-induced multisensory illusion reflects the successful integration of real and imagined cross-modal sensory stimuli, and more generally, that what we imagine hearing can change what we see.

Human brain contains of approximately 100 billion neurons. Each neuron communicates with few ten thousands of other neurons in order to carry messages in the brain. Significant electrical activity is produced in the brain over synaptic joints of such neurons sending signals at very low frequencies below (50 Hz), thereby forming the brainwave pattern. The brainwaves are categorized as delta, theta, alpha and beta, as per different frequency ranges. In this paper, the effect of binaural beats on human mind is presented. Alpha binaural beats of 10 Hz are produced by creating the auditory illusion of 10 Hz in the brain by playing the binaural beats of 370 Hz and 380 Hz for left and right ear respectively. Binaural beats are effective only when heard through an earphone. In order to examine the effects of binaural beats on human brain, 10 people are subjected to these beats for 3 minutes. Using Matlab, the attention level and meditation levels are measured by alpha brainwaves, and the comparison graphs are plotted. Relative comparison is carried out for each persons state while listening to the binaural beats. This study provides scientific evidences for the common perception that alpha binaural beats and thus music can help a person in achieving a relaxed state of mind i.e., meditative state in a better way.

Binaural beats are an auditory illusion perceived when two different pure-tone sine waves are presented one to each ear at a steady intensity and frequency. We evaluated their effectiveness in reducing preoperative anxiety in dentistry. Sixty patients (30 in each group) who were to have impacted third molars removed were studied (experimental group: 20 women and 10 men, mean (range) age 24 (18-35) years, and control group: 22 women and 8 men, mean (range) age 28 (15-47) years). All patients were fully informed about the operation preoperatively, and their anxiety recorded on a visual analogue scale (VAS). The local anaesthetic was given and the patients waited for 10minutes, during which those in the experimental group were asked to listen to binaural beats through stereo earphones (200Hz for the left ear and 209.3Hz for the right ear). No special treatment was given to the control group. In both groups anxiety was then recorded again, and the tooth removed in the usual way. The paired t test and t test were used to assess the significance of differences between groups. The degree of anxiety in the control group was unchanged after the second measurement (p=0.625), while that in the experimental group showed a significant reduction in anxiety (p=0.001). We conclude that binaural beats may be useful in reducing preoperative anxiety in dentistry.

In a complex acoustic environment, acoustic cues and attention interact in the formation of streams within the auditory scene. In this study, a variant of the “octave illusion” [Deutsch (1974). Nature 251, 307–309] was used to investigate the neural correlates of auditory streaming, and to elucidate the effects of attention on the interaction between sequential and concurrent sound segregation in humans. By directing subjects' attention to different frequencies and ears, it was possible to elicit several different illusory percepts with the identical stimulus. The first experiment tested the hypothesis that the illusion depends on the ability of listeners to perceptually stream the target tones from within the alternating sound sequences. In the second experiment, concurrent psychophysical measures and electroencephalography recordings provided neural correlates of the various percepts elicited by the multistable stimulus. The results show that the perception and neural correlates of the auditory illusion can be manipulated robustly by attentional focus and that the illusion is constrained in much the same way as auditory stream segregation, suggesting common underlying mechanisms.

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.

This study investigates the neural correlates and processes underlying the ambiguous percept produced by a stimulus similar to Deutsch's ‘octave illusion’, in which each ear is presented with a sequence of alternating pure tones of low and high frequencies. The same sequence is presented to each ear, but in opposite phase, such that the left and right ears receive a high–low–high … and a low–high–low … pattern, respectively. Listeners generally report hearing the illusion of an alternating pattern of low and high tones, with all the low tones lateralized to one side and all the high tones lateralized to the other side. The current explanation of the illusion is that it reflects an illusory feature conjunction of pitch and perceived location. Using psychophysics and electroencephalogram measures, we test this and an alternative hypothesis involving synchronous and sequential stream segregation, and investigate potential neural correlates of the illusion. We find that the illusion of alternating tones arises from the synchronous tone pairs across ears rather than sequential tones in one ear, suggesting that the illusion involves a misattribution of time across perceptual streams, rather than a misattribution of location within a stream. The results provide new insights into the mechanisms of binaural streaming and synchronous sound segregation. This article is part of the themed issue ‘Auditory and visual scene analysis’.

The endless scale illusion, obtained by cyclically repeating a chromatic scale made up of Shepard tones, has been used in a variety of musical works. Music psychology and neuroscience has been interested in this particular psychoacoustic phenomenon mainly for studying the cognitive processes of pitch perception involved. In the present study, we investigated the emotional states induced by the Shepard-Risset glissando, a variant of the Shepard scale. For this purpose we chose three musical stimuli: a Matlab-generated Shepard Risset glissando, Jean-Claude Risset's Computer Suite from Little Boy, which presents a Shepard-Risset glissando integrated in the aesthetic context of a composition, and an ordinary orchestral glissando taken from the opening of Iannis Xenakis's Metastasis. Seventy-three volunteers completed a listening experiment during which they rated their emotional response to these stimuli on a seven-point Likert scale and indicated whether they had experienced a disruption of equilibrium. Personality was also measured with the Five-Factor Model of personality traits. The results show that negative emotions were most strongly evoked during listening to each of the stimuli. We also found that the Shepard-Risset glissando illusion, both within the aesthetic context of a musical composition and on its own, was capable of evoking disruption of equilibrium, frequently leading to the associated feeling of falling. Moreover, generally for the Shepard-Risset glissando illusion, higher negative emotional ratings were given by individuals who had experienced a feeling of disturbance of equilibrium relative to those who had not had this experience. Finally, we found a complex pattern of relationships between personality and the subjective experience of the glissando. Openness to experience correlated positively with positive emotion ratings for the Computer Suite, while agreeableness correlated negatively with positive emotion ratings for the Matlab stimulus. Moreover, results indicated higher (Bonferroni-uncorrected) neuroticism for those who experienced an equilibrium disturbance relative to subjects who did not have this experience during listening to the Computer Suite. These findings suggest that musical paradoxes may be of interest not only for the insights they provide on our perceptual system, but also for the richness of the emotional experience elicited during listening.

In the Speech-to-Song Illusion, repetition of a spoken phrase results in it being perceived as if it were sung. Although a number of previous studies have examined which characteristics of the stimulus will produce the illusion, there is, until now, no description of the cognitive mechanism that underlies the illusion. We suggest that the processes found in Node Structure Theory that are used to explain normal language processing as well as other auditory illusions might also account for the Speech-to-Song Illusion. In six experiments we tested whether the satiation of lexical nodes, but continued priming of syllable nodes may lead to the Speech-to-Song Illusion. The results of these experiments provide evidence for the role of priming, activation, and satiation as described in Node Structure Theory as an explanation of the Speech-to-Song Illusion.