Music and the Auditory Brain: Where is the Connection?

Sound processing by the auditory system is understood in unprecedented details, even compared with sensory coding in the visual system. Nevertheless, we do not understand yet the way in which some of the simplest perceptual properties of sounds are coded in neuronal activity. This poses serious difficulties for linking neuronal responses in the auditory system and music processing, since music operates on abstract representations of sounds. Paradoxically, although perceptual representations of sounds most probably occur high in auditory system or even beyond it, neuronal responses are strongly affected by the temporal organization of sound streams even in subcortical stations. Thus, to the extent that music is organized sound, it is the organization, rather than the sound, which is represented first in the auditory brain

On the Perceptual Organization of Speech

A general account of auditory perceptual organization has developed in the past 2 decades. It relies on primitive devices akin to the Gestalt principles of organization to assign sensory elements to probable groupings and invokes secondary schematic processes to confirm or to repair the possible organization. Although this conceptualization is intended to apply universally, the variety and arrangement of acoustic constituents of speech violate Gestalt principles at numerous junctures, cohering perceptually, nonetheless. The authors report 3 experiments on organization in phonetic perception, using sine wave synthesis to evade the Gestalt rules and the schematic processes alike. These findings falsify a general auditory account, showing that phonetic perceptual organization is achieved by specific sensitivity to the acoustic modulations characteristic of speech signals

Auditory multistability and neurotransmitter concentrations in the human brain

Multistability in perception is a powerful tool for investigating sensory–perceptual transformations, because it produces dissociations between sensory inputs and subjective experience. Spontaneous switching between different perceptual objects occurs during prolonged listening to a sound sequence of tone triplets or repeated words (termed auditory streaming and verbal transformations, respectively). We used these examples of auditory multistability to examine to what extent neurochemical and cognitive factors influence the observed idiosyncratic patterns of switching between perceptual objects. The concentrations of glutamate–glutamine (Glx) and γ-aminobutyric acid (GABA) in brain regions were measured by magnetic resonance spectroscopy, while personality traits and executive functions were assessed using questionnaires and response inhibition tasks. Idiosyncratic patterns of perceptual switching in the two multistable stimulus configurations were identified using a multidimensional scaling (MDS) analysis. Intriguingly, although switching patterns within each individual differed between auditory streaming and verbal transformations, similar MDS dimensions were extracted separately from the two datasets. Individual switching patterns were significantly correlated with Glx and GABA concentrations in auditory cortex and inferior frontal cortex but not with the personality traits and executive functions. Our results suggest that auditory perceptual organization depends on the balance between neural excitation and inhibition in different brain regions. This article is part of the themed issue ‘Auditory and visual scene analysis'

Effect of neurofeedback on perceptual organization, visual and auditory memory in children with attention deficit/hyperactivity disorder

 Abstract ObjectivesNeurofeedback is a noninvasive treatment that changes brain activity in children with attention-deficit/hyperactivity disorder and thereby improves performance in these children. We examined the effect of neurofeedback on perceptual organization, visual and auditory memory in children with attention-deficit/hyperactivity disorder.Materials & MethodsThis study was quasi-experimental with pre-test, post-test design, and control group. The sample included 20 children with attention-deficit/hyperactivity disorder were selected through convenience sampling in Khorramabad, central Iran in 2017. The sample was divided into control and experimental groups. Pre-test included Rey-Osterrieth complex figure and Wechsler digit span. Rey-Osterrieth complex figure test was used to measure perceptual organization and visual memory. Wechsler digit span was used to measure auditory memory. After conducting pre-test, the experimental group participated in neurofeedback training sessions. Theta/Beta protocol was applied for all participants. The control group did not receive any intervention. Then post-test was conducted on two groups. ResultsNeurofeedback training significantly improved visual memory (P<0.001) but neurofeedback training had no significant effect on the perceptual organization (P>0.05). Moreover, neurofeedback training enhanced auditory short-term memory and auditory working memory (P<0.05).ConclusionNeurofeedback improved neurocognitive abilities in children with attention-deficit/hyperactivity disorder

Neurophysiological Mechanisms Involved in Auditory Perceptual Organization

In our complex acoustic environment, we are confronted with a mixture of sounds produced by several simultaneous sources. However, we rarely perceive these sounds as incomprehensible noise. Our brain uses perceptual organization processes to independently follow the emission of each sound source over time. If the acoustic properties exploited in these processes are well-established, the neurophysiological mechanisms involved in auditory scene analysis remain unclear and have recently raised more interest. Here, we review the studies investigating these mechanisms using electrophysiological recordings from the cochlear nucleus to the auditory cortex, in animals and humans. Their findings reveal that basic mechanisms such as frequency selectivity, forward suppression and multi-second habituation shape the automatic brain responses to sounds in a way that can account for several important characteristics of perceptual organization of both simultaneous and successive sounds. One challenging question remains unresolved: how are the resulting activity patterns integrated to yield the corresponding conscious percepts

Different roles of similarity and predictability in auditory stream segregation

Sound sources often emit trains of discrete sounds, such as a series of footsteps. Previously, two dif¬ferent principles have been suggested for how the human auditory system binds discrete sounds to¬gether into perceptual units. The feature similarity principle is based on linking sounds with similar characteristics over time. The predictability principle is based on linking sounds that follow each other in a predictable manner. The present study compared the effects of these two principles. Participants were presented with tone sequences and instructed to continuously indicate whether they perceived a single coherent sequence or two concurrent streams of sound. We investigated the influence of separate manipulations of similarity and predictability on these perceptual reports. Both grouping principles affected perception of the tone sequences, albeit with different characteristics. In particular, results suggest that whereas predictability is only analyzed for the currently perceived sound organization, feature similarity is also analyzed for alternative groupings of sound. Moreover, changing similarity or predictability within an ongoing sound sequence led to markedly different dynamic effects. Taken together, these results provide evidence for different roles of similarity and predictability in auditory scene analysis, suggesting that forming auditory stream representations and competition between alter¬natives rely on partly different processes

Abnormal auditory tonotopy in patients with schizophrenia

Auditory hallucinations are among the most prevalent and most distressing symptoms of schizophrenia. Despite significant progress, it is still unclear whether auditory hallucinations arise from abnormalities in primary sensory processing or whether they represent failures of higher-order functions. To address this knowledge gap, we capitalized on the increased spatial resolution afforded by ultra-high field imaging at 7 Tesla to investigate the tonotopic organization of the auditory cortex in patients with schizophrenia with a history of recurrent hallucinations. Tonotopy is a fundamental feature of the functional organization of the auditory cortex that is established very early in development and predates the onset of symptoms by decades. Compared to healthy participants, patients showed abnormally increased activation and altered tonotopic organization of the auditory cortex during a purely perceptual task, which involved passive listening to tones across a range of frequencies (88-8000 Hz). These findings suggest that the predisposition to auditory hallucinations is likely to be predicated on abnormalities in the functional organization of the auditory cortex and which may serve as a biomarker for the early identification of vulnerable individuals

Perceptual bistability in auditory streaming: how much do stimulus features matter?

The auditory two-tone streaming paradigm has been used extensively to study the mechanisms that underlie the decomposition of the auditory input into coherent sound sequences. Using longer tone sequences than usual in the literature, we show that listeners hold their first percept of the sound se¬quence for a relatively long period, after which perception switches between two or more alternative sound organizations, each held on average for a much shorter duration. The first percept also differs from subsequent ones in that stimulus parameters influence its quality and duration to a far greater degree than the subsequent ones. We propose an account of auditory streaming in terms of rivalry be¬tween competing temporal associations based on two sets of processes. The formation of associations (discovery of alternative interpretations) mainly affects the first percept by determining which sound group is discovered first and how long it takes for alternative groups to be established. In contrast, sub¬sequent percepts arise from stochastic switching between the alternatives, the dynamics of which are determined by competitive interactions between the set of coexisting interpretations

Sound predictability as a higher-order cue in auditory scene analysis

A major challenge for the auditory system is to disentangle signals emitted by two or more sound sources that are active in a temporally interleaved manner (sequential stream segregation). Besides distinct characteristics of the individual signals (e.g., their timbre, location, and pitch), one important cue for distinguishing the sound sources is how their emitted signals unfold over time. It seems intuitively plausible that signals that unfold predictably with respect to their acoustic features and time-points of occurrence, such as the repetitive signature of a train moving on the rails, can be more readily identified as originating from one sound source. Based on this rationale, predictive elements have successfully been incorporated into computational models of auditory scene analysis for many years

Modulation-frequency acts as a primary cue for auditory stream segregation

In our surrounding acoustic world sounds are produced by different sources and interfere with each other before arriving to the ears. A key function of the auditory system is to provide consistent and robust descriptions of the coherent sound groupings and sequences (auditory objects), which likely correspond to the various sound sources in the environment. This function has been termed auditory stream segregation. In the current study we tested the effects of separation in the frequency of amplitude modulation on the segregation of concurrent sound sequences in the auditory stream-segregation paradigm (van Noorden 1975). The aim of the study was to assess 1) whether differential amplitude modulation would help in separating concurrent sound sequences and 2) whether this cue would interact with previously studied static cues (carrier frequency and location difference) in segregating concurrent streams of sound. We found that amplitude modulation difference is utilized as a primary cue for the stream segregation and it interacts with other primary cues such as frequency and location difference