Attention-Driven Modulation of Auditory Cortex Activity during Selective Listening in a Multispeaker Setting.

Real-world listening settings often consist of multiple concurrent sound streams. To limit perceptual interference during selective listening, the auditory system segregates and filters the relevant sensory input. Previous work provided evidence that the auditory cortex is critically involved in this process and selectively gates attended input toward subsequent processing stages. We studied at which level of auditory cortex processing this filtering of attended information occurs using functional magnetic resonance imaging (fMRI) and a naturalistic selective listening task. Forty-five human listeners (of either sex) attended to one of two continuous speech streams, presented either concurrently or in isolation. Functional data were analyzed using an inter-subject analysis to assess stimulus-specific components of ongoing auditory cortex activity. Our results suggest that stimulus-related activity in the primary auditory cortex and the adjacent planum temporale are hardly affected by attention, whereas brain responses at higher stages of the auditory cortex processing hierarchy become progressively more selective for the attended input. Consistent with these findings, a complementary analysis of stimulus-driven functional connectivity further demonstrated that information on the to-be-ignored speech stream is shared between the primary auditory cortex and the planum temporale but largely fails to reach higher processing stages. Our findings suggest that the neural processing of ignored speech cannot be effectively suppressed at the level of early cortical processing of acoustic features but is gradually attenuated once the competing speech streams are fully segregated.

Cortical-subcortical interactions underlie processing of auditory predictions measured with 7T fMRI.

Perception integrates both sensory inputs and internal models of the environment. In the auditory domain, predictions play a critical role because of the temporal nature of sounds. However, the precise contribution of cortical and subcortical structures in these processes and their interaction remain unclear. It is also unclear whether these brain interactions are specific to abstract rules or if they also underlie the predictive coding of local features. We used high-field 7T functional magnetic resonance imaging to investigate interactions between cortical and subcortical areas during auditory predictive processing. Volunteers listened to tone sequences in an oddball paradigm where the predictability of the deviant was manipulated. Perturbations in periodicity were also introduced to test the specificity of the response. Results indicate that both cortical and subcortical auditory structures encode high-order predictive dynamics, with the effect of predictability being strongest in the auditory cortex. These predictive dynamics were best explained by modeling a top-down information flow, in contrast to unpredicted responses. No error signals were observed to deviations of periodicity, suggesting that these responses are specific to abstract rule violations. Our results support the idea that the high-order predictive dynamics observed in subcortical areas propagate from the auditory cortex.

Training allows switching from limited-capacity manipulations to large-capacity perceptual processing.

In contrast to perceptual tasks, which enable concurrent processing of many stimuli, working memory (WM) tasks have a very small capacity, limiting cognitive skills. Training on WM tasks often yields substantial improvement, suggesting that training might increase the general WM capacity. To understand the underlying processes, we trained a test group with a newly designed tone manipulation WM task and a control group with a challenging perceptual task of pitch pattern discrimination. Functional magnetic resonance imaging (fMRI) scans confirmed that pretraining, manipulation was associated with a dorsal fronto-parietal WM network, while pitch comparison was associated with activation of ventral auditory regions. Training induced improvement in each group, which was limited to the trained task. Analyzing the behavior of the group trained with tone manipulation revealed that participants learned to replace active manipulation with a perceptual verification of the position of a single salient tone in the sequence presented as a tentative reply. Posttraining fMRI scans revealed modifications in ventral activation of both groups. Successful WMtrained participants learned to utilize auditory regions for the trained task. These observations suggest that the huge task-specific enhancement of WM capacity stems from a task-specific switch to perceptual routines, implemented in perceptual regions.

Music and Brain Circuitry: Strategies for Strengthening Evidence-Based Research for Music-Based Interventions.

The neuroscience of music and music-based interventions (MBIs) is a fascinating but challenging research field. While music is a ubiquitous component of every human society, MBIs may encompass listening to music, performing music, music-based movement, undergoing music education and training, or receiving treatment from music therapists. Unraveling the brain circuits activated and influenced by MBIs may help us gain better understanding of the therapeutic and educational values of MBIs by gathering strong research evidence. However, the complexity and variety of MBIs impose unique research challenges. This article reviews the recent endeavor led by the National Institutes of Health to support evidence-based research of MBIs and their impact on health and diseases. It also highlights fundamental challenges and strategies of MBI research with emphases on the utilization of animal models, human brain imaging and stimulation technologies, behavior and motion capturing tools, and computational approaches. It concludes with suggestions of basic requirements when studying MBIs and promising future directions to further strengthen evidence-based research on MBIs in connections with brain circuitry.SIGNIFICANCE STATEMENT Music and music-based interventions (MBI) engage a wide range of brain circuits and hold promising therapeutic potentials for a variety of health conditions. Comparative studies using animal models have helped in uncovering brain circuit activities involved in rhythm perception, while human imaging, brain stimulation, and motion capture technologies have enabled neural circuit analysis underlying the effects of MBIs on motor, affective/reward, and cognitive function. Combining computational analysis, such as prediction method, with mechanistic studies in animal models and humans may unravel the complexity of MBIs and their effects on health and disease.

Development and validation of an fMRI-informed EEG model of reward-related ventral striatum activation.

Reward processing is essential for our mental-health and well-being. In the current study, we developed and validated a scalable, fMRI-informed EEG model for monitoring reward processing related to activation in the ventral-striatum (VS), a significant node in the brain's reward system. To develop this EEG-based model of VS-related activation, we collected simultaneous EEG/fMRI data from 17 healthy individuals while listening to individually-tailored pleasurable music - a highly rewarding stimulus known to engage the VS. Using these cross-modal data, we constructed a generic regression model for predicting the concurrently acquired Blood-Oxygen-Level-Dependent (BOLD) signal from the VS using spectro-temporal features from the EEG signal (termed hereby VS-related-Electrical Finger Print; VS-EFP). The performance of the extracted model was examined using a series of tests that were applied on the original dataset and, importantly, an external validation dataset collected from a different group of 14 healthy individuals who underwent the same EEG/FMRI procedure. Our results showed that the VS-EFP model, as measured by simultaneous EEG, predicted BOLD activation in the VS and additional functionally relevant regions to a greater extent than an EFP model derived from a different anatomical region. The developed VS-EFP was also modulated by musical pleasure and predictive of the VS-BOLD during a monetary reward task, further indicating its functional relevance. These findings provide compelling evidence for the feasibility of using EEG alone to model neural activation related to the VS, paving the way for future use of this scalable neural probing approach in neural monitoring and self-guided neuromodulation.

Using cortico-cerebellar structural patterns to classify early- and late-trained musicians.

A body of current evidence suggests that there is a sensitive period for musical training: people who begin training before the age of seven show better performance on tests of musical skill, and also show differences in brain structure-especially in motor cortical and cerebellar regions-compared with those who start later. We used support vector machine models-a subtype of supervised machine learning-to investigate distributed patterns of structural differences between early-trained (ET) and late-trained (LT) musicians and to better understand the age boundaries of the sensitive period for early musicianship. After selecting regions of interest from the cerebellum and cortical sensorimotor regions, we applied recursive feature elimination with cross-validation to produce a model which optimally and accurately classified ET and LT musicians. This model identified a combination of 17 regions, including 9 cerebellar and 8 sensorimotor regions, and maintained a high accuracy and sensitivity (true positives, i.e., ET musicians) without sacrificing specificity (true negatives, i.e., LT musicians). Critically, this model-which defined ET musicians as those who began their training before the age of 7-outperformed all other models in which age of start was earlier or later (between ages 5-10). Our model's ability to accurately classify ET and LT musicians provides additional evidence that musical training before age 7 affects cortico-cerebellar structure in adulthood, and is consistent with the hypothesis that connected brain regions interact during development to reciprocally influence brain and behavioral maturation.

Unraveling the Temporal Dynamics of Reward Signals in Music-Induced Pleasure with TMS.

Music's ability to induce feelings of pleasure has been the subject of intense neuroscientific research lately. Prior neuroimaging studies have shown that music-induced pleasure engages cortico-striatal circuits related to the anticipation and receipt of biologically relevant rewards/incentives, but these reports are necessarily correlational. Here, we studied both the causal role of this circuitry and its temporal dynamics by applying transcranial magnetic stimulation (TMS) over the left dorsolateral PFC combined with fMRI in 17 male and female participants. Behaviorally, we found that, in accord with previous findings, excitation of fronto-striatal pathways enhanced subjective reports of music-induced pleasure and motivation, whereas inhibition of the same circuitry led to the reduction of both. fMRI activity patterns indicated that these behavioral changes were driven by bidirectional TMS-induced alteration of fronto-striatal function. Specifically, changes in activity in the NAcc predicted modulation of both hedonic and motivational responses, with a dissociation between pre-experiential versus experiential components of musical reward. In addition, TMS-induced changes in the fMRI functional connectivity between the NAcc and frontal and auditory cortices predicted the degree of modulation of hedonic responses. These results indicate that the engagement of cortico-striatal pathways and the NAcc, in particular, is indispensable to experience rewarding feelings from music.SIGNIFICANCE STATEMENT Neuroimaging studies have shown that music-induced pleasure engages cortico-striatal circuits involved in the processing of biologically relevant rewards. Yet, these reports are necessarily correlational. Here, we studied both the causal role of this circuitry and its temporal dynamics by combining brain stimulation over the frontal cortex with functional imaging. Behaviorally, we found that excitation and inhibition of fronto-striatal pathways enhanced and disrupted, respectively, subjective reports of music-induced pleasure and motivation. These changes were associated with changes in NAcc activity and NAcc coupling with frontal and auditory cortices, dissociating between pre-experimental versus experiential components of musical reward. These results indicate that the engagement of cortico-striatal pathways, and the NAcc in particular, is indispensable to experience rewarding feeling from music.

MEG Intersubject Phase Locking of Stimulus-Driven Activity during Naturalistic Speech Listening Correlates with Musical Training.

Musical training is associated with increased structural and functional connectivity between auditory sensory areas and higher-order brain networks involved in speech and motor processing. Whether such changed connectivity patterns facilitate the cortical propagation of speech information in musicians remains poorly understood. We here used magnetoencephalography (MEG) source imaging and a novel seed-based intersubject phase-locking approach to investigate the effects of musical training on the interregional synchronization of stimulus-driven neural responses during listening to naturalistic continuous speech presented in silence. MEG data were obtained from 20 young human subjects (both sexes) with different degrees of musical training. Our data show robust bilateral patterns of stimulus-driven interregional phase synchronization between auditory cortex and frontotemporal brain regions previously associated with speech processing. Stimulus-driven phase locking was maximal in the delta band, but was also observed in the theta and alpha bands. The individual duration of musical training was positively associated with the magnitude of stimulus-driven alpha-band phase locking between auditory cortex and parts of the dorsal and ventral auditory processing streams. These findings provide evidence for a positive relationship between musical training and the propagation of speech-related information between auditory sensory areas and higher-order processing networks, even when speech is presented in silence. We suggest that the increased synchronization of higher-order cortical regions to auditory cortex may contribute to the previously described musician advantage in processing speech in background noise.SIGNIFICANCE STATEMENT Musical training has been associated with widespread structural and functional brain plasticity. It has been suggested that these changes benefit the production and perception of music but can also translate to other domains of auditory processing, such as speech. We developed a new magnetoencephalography intersubject analysis approach to study the cortical synchronization of stimulus-driven neural responses during the perception of continuous natural speech and its relationship to individual musical training. Our results provide evidence that musical training is associated with higher synchronization of stimulus-driven activity between brain regions involved in early auditory sensory and higher-order processing. We suggest that the increased synchronized propagation of speech information may contribute to the previously described musician advantage in processing speech in background noise.

Oscillatory Entrainment of the Frequency-following Response in Auditory Cortical and Subcortical Structures.

There is much debate about the existence and function of neural oscillatory mechanisms in the auditory system. The frequency-following response (FFR) is an index of neural periodicity encoding that can provide a vehicle to study entrainment in frequency ranges relevant to speech and music processing. Criteria for entrainment include the presence of poststimulus oscillations and phase alignment between stimulus and endogenous activity. To test the hypothesis of entrainment, in experiment 1 we collected FFR data for a repeated syllable using magnetoencephalography (MEG) and electroencephalography in 20 male and female human adults. We observed significant oscillatory activity after stimulus offset in auditory cortex and subcortical auditory nuclei, consistent with entrainment. In these structures, the FFR fundamental frequency converged from a lower value over 100 ms to the stimulus frequency, consistent with phase alignment, and diverged to a lower value after offset, consistent with relaxation to a preferred frequency. In experiment 2, we tested how transitions between stimulus frequencies affected the MEG FFR to a train of tone pairs in 30 people. We found that the FFR was affected by the frequency of the preceding tone for up to 40 ms at subcortical levels, and even longer durations at cortical levels. Our results suggest that oscillatory entrainment may be an integral part of periodic sound representation throughout the auditory neuraxis. The functional role of this mechanism is unknown, but it could serve as a fine-scale temporal predictor for frequency information, enhancing stability and reducing susceptibility to degradation that could be useful in real-life noisy environments.SIGNIFICANCE STATEMENT Neural oscillations are proposed to be a ubiquitous aspect of neural function, but their contribution to auditory encoding is not clear, particularly at higher frequencies associated with pitch encoding. In a magnetoencephalography experiment, we found converging evidence that the frequency-following response has an oscillatory component according to established criteria: poststimulus resonance, progressive entrainment of the neural frequency to the stimulus frequency, and relaxation toward the original state on stimulus offset. In a second experiment, we found that the frequency and amplitude of the frequency-following response to tones are affected by preceding stimuli. These findings support the contribution of intrinsic oscillations to the encoding of sound, and raise new questions about their functional roles, possibly including stabilization and low-level predictive coding.

Rhythm and time in the premotor cortex.

Many animals can encode temporal intervals and use them to plan their actions, but only humans can flexibly extract a regular beat from complex patterns, such as musical rhythms. Beat-based timing is hypothesized to rely on the integration of sensory information with temporal information encoded in motor regions such as the medial premotor cortex (MPC), but how beat-based timing might be encoded in neuronal populations is mostly unknown. Gámez and colleagues show that the MPC encodes temporal information via a population code visible as circular trajectories in state space; these patterns may represent precursors to more-complex skills such as beat-based timing.

The Microstructural Plasticity of the Arcuate Fasciculus Undergirds Improved Speech in Noise Perception in Musicians.

Musical training is thought to be related to improved language skills, for example, understanding speech in background noise. Although studies have found that musicians and nonmusicians differed in morphology of bilateral arcuate fasciculus (AF), none has associated such white matter features with speech-in-noise (SIN) perception. Here, we tested both SIN and the diffusivity of bilateral AF segments in musicians and nonmusicians using diffusion tensor imaging. Compared with nonmusicians, musicians had higher fractional anisotropy (FA) in the right direct AF and lower radial diffusivity in the left anterior AF, which correlated with SIN performance. The FA-based laterality index showed stronger right lateralization of the direct AF and stronger left lateralization of the posterior AF in musicians than nonmusicians, with the posterior AF laterality predicting SIN accuracy. Furthermore, hemodynamic activity in right superior temporal gyrus obtained during a SIN task played a full mediation role in explaining the contribution of the right direct AF diffusivity on SIN performance, which therefore links training-related white matter plasticity, brain hemodynamics, and speech perception ability. Our findings provide direct evidence that differential microstructural plasticity of bilateral AF segments may serve as a neural foundation of the cross-domain transfer effect of musical experience to speech perception amid competing noise.

Mapping Specific Mental Content during Musical Imagery.

Humans can mentally represent auditory information without an external stimulus, but the specificity of these internal representations remains unclear. Here, we asked how similar the temporally unfolding neural representations of imagined music are compared to those during the original perceived experience. We also tested whether rhythmic motion can influence the neural representation of music during imagery as during perception. Participants first memorized six 1-min-long instrumental musical pieces with high accuracy. Functional MRI data were collected during: 1) silent imagery of melodies to the beat of a visual metronome; 2) same but while tapping to the beat; and 3) passive listening. During imagery, inter-subject correlation analysis showed that melody-specific temporal response patterns were reinstated in right associative auditory cortices. When tapping accompanied imagery, the melody-specific neural patterns were reinstated in more extensive temporal-lobe regions bilaterally. These results indicate that the specific contents of conscious experience are encoded similarly during imagery and perception in the dynamic activity of auditory cortices. Furthermore, rhythmic motion can enhance the reinstatement of neural patterns associated with the experience of complex sounds, in keeping with models of motor to sensory influences in auditory processing.

Musical reward prediction errors engage the nucleus accumbens and motivate learning.

Enjoying music reliably ranks among life's greatest pleasures. Like many hedonic experiences, it engages several reward-related brain areas, with activity in the nucleus accumbens (NAc) most consistently reflecting the listener's subjective response. Converging evidence suggests that this activity arises from musical "reward prediction errors" (RPEs) that signal the difference between expected and perceived musical events, but this hypothesis has not been directly tested. In the present fMRI experiment, we assessed whether music could elicit formally modeled RPEs in the NAc by applying a well-established decision-making protocol designed and validated for studying RPEs. In the scanner, participants chose between arbitrary cues that probabilistically led to dissonant or consonant music, and learned to make choices associated with the consonance, which they preferred. We modeled regressors of trial-by-trial RPEs, finding that NAc activity tracked musically elicited RPEs, to an extent that explained variance in the individual learning rates. These results demonstrate that music can act as a reward, driving learning and eliciting RPEs in the NAc, a hub of reward- and music enjoyment-related activity.

Dopamine modulates the reward experiences elicited by music.

Understanding how the brain translates a structured sequence of sounds, such as music, into a pleasant and rewarding experience is a fascinating question which may be crucial to better understand the processing of abstract rewards in humans. Previous neuroimaging findings point to a challenging role of the dopaminergic system in music-evoked pleasure. However, there is a lack of direct evidence showing that dopamine function is causally related to the pleasure we experience from music. We addressed this problem through a double blind within-subject pharmacological design in which we directly manipulated dopaminergic synaptic availability while healthy participants (n = 27) were engaged in music listening. We orally administrated to each participant a dopamine precursor (levodopa), a dopamine antagonist (risperidone), and a placebo (lactose) in three different sessions. We demonstrate that levodopa and risperidone led to opposite effects in measures of musical pleasure and motivation: while the dopamine precursor levodopa, compared with placebo, increased the hedonic experience and music-related motivational responses, risperidone led to a reduction of both. This study shows a causal role of dopamine in musical pleasure and indicates that dopaminergic transmission might play different or additive roles than the ones postulated in affective processing so far, particularly in abstract cognitive activities.

Effector-independent brain network for auditory-motor integration: fMRI evidence from singing and cello playing.

Many everyday tasks share high-level sensory goals but differ in the movements used to accomplish them. One example of this is musical pitch regulation, where the same notes can be produced using the vocal system or a musical instrument controlled by the hands. Cello playing has previously been shown to rely on brain structures within the singing network for performance of single notes, except in areas related to primary motor control, suggesting that the brain networks for auditory feedback processing and sensorimotor integration may be shared (Segado et al. 2018). However, research has shown that singers and cellists alike can continue singing/playing in tune even in the absence of auditory feedback (Chen et al. 2013, Kleber et al. 2013), so different paradigms are required to test feedback monitoring and control mechanisms. In singing, auditory pitch feedback perturbation paradigms have been used to show that singers engage a network of brain regions including anterior cingulate cortex (ACC), anterior insula (aINS), and intraparietal sulcus (IPS) when compensating for altered pitch feedback, and posterior superior temporal gyrus (pSTG) and supramarginal gyrus (SMG) when ignoring it (Zarate et al. 2005, 2008). To determine whether the brain networks for cello playing and singing directly overlap in these sensory-motor integration areas, in the present study expert cellists were asked to compensate for or ignore introduced pitch perturbations when singing/playing during fMRI scanning. We found that cellists were able to sing/play target tones, and compensate for and ignore introduced feedback perturbations equally well. Brain activity overlapped for singing and playing in IPS and SMG when compensating, and pSTG and dPMC when ignoring; differences between singing/playing across all three conditions were most prominent in M1, centered on the relevant motor effectors (hand, larynx). These findings support the hypothesis that pitch regulation during cello playing relies on structures within the singing network and suggests that differences arise primarily at the level of forward motor control.

Inhibitory effect of tDCS on auditory evoked response: Simultaneous MEG-tDCS reveals causal role of right auditory cortex in pitch learning.

A body of literature has demonstrated that the right auditory cortex (AC) plays a dominant role in fine pitch processing. However, our understanding is relatively limited about whether this asymmetry extends to perceptual learning of pitch. There is also a lack of causal evidence regarding the role of the right AC in pitch learning.  We addressed these points with anodal transcranial direct current stimulation (tDCS), adapting a previous behavioral study in which anodal tDCS over the right AC was shown to block improvement of a microtonal pitch pattern learning task over 3 days. To address the physiological changes associated with tDCS, we recorded MEG data simultaneously with tDCS on the first day, and measured behavioral thresholds on the following two consecutive days. We tested three groups of participants who received anodal tDCS over their right or left AC, or sham tDCS, and measured the N1m auditory evoked response before, during, and after tDCS. Our data show that anodal tDCS of the right AC disrupted pitch discrimination learning up to two days after its application, whereas learning was unaffected by left-AC or sham tDCS. Although tDCS reduced the amplitude of the N1m ipsilaterally to the stimulated hemisphere on both left and right, only right AC N1m amplitude reductions were associated with the degree to which pitch learning was disrupted. This brain-behavior relationship confirms a causal link between right AC physiological responses and fine pitch processing, and provides neurophysiological insight concerning the mechanisms of action of tDCS on the auditory system.

Neural network retuning and neural predictors of learning success associated with cello training.

The auditory and motor neural systems are closely intertwined, enabling people to carry out tasks such as playing a musical instrument whose mapping between action and sound is extremely sophisticated. While the dorsal auditory stream has been shown to mediate these audio-motor transformations, little is known about how such mapping emerges with training. Here, we use longitudinal training on a cello as a model for brain plasticity during the acquisition of specific complex skills, including continuous and many-to-one audio-motor mapping, and we investigate individual differences in learning. We trained participants with no musical background to play on a specially designed MRI-compatible cello and scanned them before and after 1 and 4 wk of training. Activation of the auditory-to-motor dorsal cortical stream emerged rapidly during the training and was similarly activated during passive listening and cello performance of trained melodies. This network activation was independent of performance accuracy and therefore appears to be a prerequisite of music playing. In contrast, greater recruitment of regions involved in auditory encoding and motor control over the training was related to better musical proficiency. Additionally, pre-supplementary motor area activity and its connectivity with the auditory cortex during passive listening before training was predictive of final training success, revealing the integrative function of this network in auditory-motor information processing. Together, these results clarify the critical role of the dorsal stream and its interaction with auditory areas in complex audio-motor learning.

White Matter Microstructure Reflects Individual Differences in Music Reward Sensitivity.

People show considerable variability in the degree of pleasure they experience from music. These individual differences in music reward sensitivity are driven by variability in functional connectivity between the nucleus accumbens (NAcc), a key structure of the reward system, and the right superior temporal gyrus (STG). However, it is unknown whether a neuroanatomical basis exists for this variability. We used diffusion tensor imaging and probabilistic tractography to study the relationship between music reward sensitivity and white matter microstructure connecting these two regions via the orbitofrontal cortex (OFC) in 38 healthy human participants (24 females and 14 males). We found that right axial diffusivity (AD) in the STG-OFC connectivity inversely correlated with music reward sensitivity. Additionally, right mean diffusivity and left AD in the NAcc-OFC tract also showed an inverse correlation. Further, AD in this tract also correlated with previously acquired BOLD activity during music listening, but not for a control monetary reward task in the NAcc. Finally, we used mediation analysis to show that AD in the NAcc-OFC tract explains the influence of NAcc activation during a music task on music reward sensitivity. Overall, our results provide further support for the idea that the exchange of information among perceptual, integrative, and reward systems is important for musical pleasure, and that individual differences in the structure of the relevant anatomical connectivity influences the degree to which people are able to derive such pleasure.SIGNIFICANCE STATEMENT Music is one of the most important sources of pleasure for many people, but at the same time there are important individual differences in the sensitivity to musical reward. Previous studies have revealed the critical involvement of the functional connectivity between perceptual and subcortical brain areas in the enjoyment of music. However, it is unknown whether individual differences in music sensitivity might arise from variability in the structural connectivity among these areas. Here we show that structural connectivity between supratemporal and orbitofrontal cortices, and between orbitofrontal and nucleus accumbens, predict individual differences in sensibility to music reward. These results provide evidence for the critical involvement of the interaction between the subcortical reward system and higher-order cortical areas in music-induced pleasure.

Predictability and Uncertainty in the Pleasure of Music: A Reward for Learning?

Music ranks among the greatest human pleasures. It consistently engages the reward system, and converging evidence implies it exploits predictions to do so. Both prediction confirmations and errors are essential for understanding one's environment, and music offers many of each as it manipulates interacting patterns across multiple timescales. Learning models suggest that a balance of these outcomes (i.e., intermediate complexity) optimizes the reduction of uncertainty to rewarding and pleasurable effect. Yet evidence of a similar pattern in music is mixed, hampered by arbitrary measures of complexity. In the present studies, we applied a well-validated information-theoretic model of auditory expectation to systematically measure two key aspects of musical complexity: predictability (operationalized as information content [IC]), and uncertainty (entropy). In Study 1, we evaluated how these properties affect musical preferences in 43 male and female participants; in Study 2, we replicated Study 1 in an independent sample of 27 people and assessed the contribution of veridical predictability by presenting the same stimuli seven times. Both studies revealed significant quadratic effects of IC and entropy on liking that outperformed linear effects, indicating reliable preferences for music of intermediate complexity. An interaction between IC and entropy further suggested preferences for more predictability during more uncertain contexts, which would facilitate uncertainty reduction. Repeating stimuli decreased liking ratings but did not disrupt the preference for intermediate complexity. Together, these findings support long-hypothesized optimal zones of predictability and uncertainty in musical pleasure with formal modeling, relating the pleasure of music listening to the intrinsic reward of learning.SIGNIFICANCE STATEMENT Abstract pleasures, such as music, claim much of our time, energy, and money despite lacking any clear adaptive benefits like food or shelter. Yet as music manipulates patterns of melody, rhythm, and more, it proficiently exploits our expectations. Given the importance of anticipating and adapting to our ever-changing environments, making and evaluating uncertain predictions can have strong emotional effects. Accordingly, we present evidence that listeners consistently prefer music of intermediate predictive complexity, and that preferences shift toward expected musical outcomes in more uncertain contexts. These results are consistent with theories that emphasize the intrinsic reward of learning, both by updating inaccurate predictions and validating accurate ones, which is optimal in environments that present manageable predictive challenges (i.e., reducible uncertainty).

Musicians at the Cocktail Party: Neural Substrates of Musical Training During Selective Listening in Multispeaker Situations.

Musical training has been demonstrated to benefit speech-in-noise perception. It is however unknown whether this effect translates to selective listening in cocktail party situations, and if so what its neural basis might be. We investigated this question using magnetoencephalography-based speech envelope reconstruction and a sustained selective listening task, in which participants with varying amounts of musical training attended to 1 of 2 speech streams while detecting rare target words. Cortical frequency-following responses (FFR) and auditory working memory were additionally measured to dissociate musical training-related effects on low-level auditory processing versus higher cognitive function. Results show that the duration of musical training is associated with a reduced distracting effect of competing speech on target detection accuracy. Remarkably, more musical training was related to a robust neural tracking of both the to-be-attended and the to-be-ignored speech stream, up until late cortical processing stages. Musical training-related increases in FFR power were associated with a robust speech tracking in auditory sensory areas, whereas training-related differences in auditory working memory were linked to an increased representation of the to-be-ignored stream beyond auditory cortex. Our findings suggest that musically trained persons can use additional information about the distracting stream to limit interference by competing speech.