Neurophysiology and neuroanatomy of pitch perception: auditory cortex

Encoding of melody in the human auditory cortex

Melody is a core component of music in which discrete pitches are serially arranged to convey emotion and meaning. Perception varies along several pitch-based dimensions: (i) the absolute pitch of notes, (ii) the difference in pitch between successive notes, and (iii) the statistical expectation of each note given prior context. How the brain represents these dimensions and whether their encoding is specialized for music remains unknown. We recorded high-density neurophysiological activity directly from the human auditory cortex while participants listened to Western musical phrases. Pitch, pitch-change, and expectation were selectively encoded at different cortical sites, indicating a spatial map for representing distinct melodic dimensions. The same participants listened to spoken English, and we compared responses to music and speech. Cortical sites selective for music encoded expectation, while sites that encoded pitch and pitch-change in music used the same neural code to represent equivalent properties of speech. Findings reveal how the perception of melody recruits both music-specific and general-purpose sound representations.

Data-driven multiscale model of macaque auditory thalamocortical circuits reproduces in vivo dynamics

We developed a detailed model of macaque auditory thalamocortical circuits, including primary auditory cortex (A1), medial geniculate body (MGB), and thalamic reticular nucleus, utilizing the NEURON simulator and NetPyNE tool. The A1 model simulates a cortical column with over 12,000 neurons and 25 million synapses, incorporating data on cell-type-specific neuron densities, morphology, and connectivity across six cortical layers. It is reciprocally connected to the MGB thalamus, which includes interneurons and core and matrix-layer-specific projections to A1. The model simulates multiscale measures, including physiological firing rates, local field potentials (LFPs), current source densities (CSDs), and electroencephalography (EEG) signals. Laminar CSD patterns, during spontaneous activity and in response to broadband noise stimulus trains, mirror experimental findings. Physiological oscillations emerge spontaneously across frequency bands comparable to those recorded in vivo. We elucidate population-specific contributions to observed oscillation events and relate them to firing and presynaptic input patterns. The model offers a quantitative theoretical framework to integrate and interpret experimental data and predict its underlying cellular and circuit mechanisms.

Encoding of melody in the human auditory cortex

Melody is a core component of music in which discrete pitches are serially arranged to convey emotion and meaning. Perception of melody varies along several pitch-based dimensions: (1) the absolute pitch of notes, (2) the difference in pitch between successive notes, and (3) the higher-order statistical expectation of each note conditioned on its prior context. While humans readily perceive melody, how these dimensions are collectively represented in the brain and whether their encoding is specialized for music remains unknown. Here, we recorded high-density neurophysiological activity directly from the surface of human auditory cortex while Western participants listened to Western musical phrases. Pitch, pitch-change, and expectation were selectively encoded at different cortical sites, indicating a spatial code for representing distinct dimensions of melody. The same participants listened to spoken English, and we compared evoked responses to music and speech. Cortical sites selective for music were systematically driven by the encoding of expectation. In contrast, sites that encoded pitch and pitch-change used the same neural code to represent equivalent properties of speech. These findings reveal the multidimensional nature of melody encoding, consisting of both music-specific and domain-general sound representations in auditory cortex.

Teaser

The human brain contains both general-purpose and music-specific neural populations for processing distinct attributes of melody.

Early social communication through music: State of the art and future perspectives

A growing body of research shows that the universal capacity for music perception and production emerges early in development. Possibly building on this predisposition, caregivers around the world often communicate with infants using songs or speech entailing song-like characteristics. This suggests that music might be one of the earliest developing and most accessible forms of interpersonal communication, providing a platform for studying early communicative behavior. However, little research has examined music in truly communicative contexts. The current work aims to facilitate the development of experimental approaches that rely on dynamic and naturalistic social interactions. We first review two longstanding lines of research that examine musical interactions by focusing either on the caregiver or the infant. These include defining the acoustic and non-acoustic features that characterize infant-directed (ID) music, as well as behavioral and neurophysiological research examining infants' processing of musical timing and pitch. Next, we review recent studies looking at early musical interactions holistically. This research focuses on how caregivers and infants interact using music to achieve co-regulation, mutual engagement, and increase affiliation and prosocial behavior. We conclude by discussing methodological, technological, and analytical advances that might empower a comprehensive study of musical communication in early childhood.

Why is the perceptual octave stretched? An account based on mismatched time constants within the auditory brainstem

This paper suggests an explanation for listeners' greater tolerance to positive than negative mistuning of the higher tone within an octave pair. It hypothesizes a neural circuit tuned to cancel the lower tone that also cancels the higher tone if that tone is in tune. Imperfect cancellation is the cue to mistuning of the octave. The circuit involves two neural pathways, one delayed with respect to the other, that feed a coincidence-sensitive neuron via excitatory and inhibitory synapses. A mismatch between the time constants of these two synapses results in an asymmetry in sensitivity to mismatch. Specifically, if the time constant of the delayed pathway is greater than that of the direct pathway, there is a greater tolerance to positive mistuning than to negative mistuning. The model is directly applicable to the harmonic octave (concurrent tones) but extending it to the melodic octave (successive tones) requires additional assumptions that are discussed. The paper reviews evidence from auditory psychophysics and physiology in favor-or against-this explanation.

Critical behavior and the Kibble-Zurek mechanism in a musical phase transition

We investigate the critical phenomena emerging from a statistical mechanics model of musical harmony on a three-dimensional (3D) lattice, and the resulting structure of the ordered phase. In this model, each lattice site represents a tone, with nearest neighbors interacting via the perception of dissonance between them. With dissonance assumed to be an octave-wise periodic function of pitch difference, this model is a 3D XY system with the same symmetry and dimensionality as superfluid helium and models of the cosmological axion field. We use numerical simulation to observe a phase transition from disordered sound to ordered arrangements of musical pitches as a parameter analogous to the temperature is quenched towards zero. We observe the divergence of correlation length and relaxation time at the phase boundary, consistent with the critical exponents in similar systems. Furthermore, the quenched low-temperature phase of these systems displays topological defects in the form of vortex strings that thread throughout the system volume. We observe the formation of these vortex strings in accordance with the Kibble-Zurek mechanism, and discuss the structure of these vortex strings in the context of the theory of musical harmony, finding both similarities to established music theory, and uncovering new avenues to explore.

Functional changes in the auditory cortex and associated regions caused by different acoustic stimuli in patients with presbycusis and tinnitus

Presbycusis and tinnitus are the two most common hearing related pathologies. Although both of these conditions presumably originate in the inner ear, there are several reports concerning their central components. Interestingly, the onset of presbycusis coincides with the highest occurrence of tinnitus. The aim of this study was to identify age, hearing loss, and tinnitus related functional changes, within the auditory system and its associated structures. Seventy-eight participants were selected for the study based on their age, hearing, and tinnitus, and they were divided into six groups: young controls (Y-NH-NT), subjects with mild presbycusis (O-NH-NT) or expressed presbycusis (O-HL-NT), young subjects with tinnitus (Y-NH-T), subjects with mild presbycusis and tinnitus (O-NH-T), and subjects with expressed presbycusis and tinnitus (O-HL-T). An MRI functional study was performed with a 3T MRI system, using an event related design (different types of acoustic and visual stimulations and their combinations). The amount of activation of the auditory cortices (ACs) was dependent on the complexity of the stimuli; higher complexity resulted in a larger area of the activated cortex. Auditory stimulation produced a slightly greater activation in the elderly, with a negative effect of hearing loss (lower activation). The congruent audiovisual stimulation led to an increased activity within the default mode network, whereas incongruent stimulation led to increased activation of the visual cortex. The presence of tinnitus increased activation of the AC, specifically in the aged population, with a slight prevalence in the left AC. The occurrence of tinnitus was accompanied by increased activity within the insula and hippocampus bilaterally. Overall, we can conclude that expressed presbycusis leads to a lower activation of the AC, compared to the elderly with normal hearing; aging itself leads to increased activity in the right AC. The complexity of acoustic stimuli plays a major role in the activation of the AC, its support by visual stimulation leads to minimal changes within the AC. Tinnitus causes changes in the activity of the limbic system, as well as in the auditory AC, where it is bound to the left hemisphere.

Innate frequency-discrimination hyperacuity in Williams-Beuren syndrome mice

Williams-Beuren syndrome (WBS) is a rare disorder caused by hemizygous microdeletion of ∼27 contiguous genes. Despite neurodevelopmental and cognitive deficits, individuals with WBS have spared or enhanced musical and auditory abilities, potentially offering an insight into the genetic basis of auditory perception. Here, we report that the mouse models of WBS have innately enhanced frequency-discrimination acuity and improved frequency coding in the auditory cortex (ACx). Chemogenetic rescue showed frequency-discrimination hyperacuity is caused by hyperexcitable interneurons in the ACx. Haploinsufficiency of one WBS gene, Gtf2ird1, replicated WBS phenotypes by downregulating the neuropeptide receptor VIPR1. VIPR1 is reduced in the ACx of individuals with WBS and in the cerebral organoids derived from human induced pluripotent stem cells with the WBS microdeletion. Vipr1 deletion or overexpression in ACx interneurons mimicked or reversed, respectively, the cellular and behavioral phenotypes of WBS mice. Thus, the Gtf2ird1-Vipr1 mechanism in ACx interneurons may underlie the superior auditory acuity in WBS.

Diotic and Dichotic Mechanisms of Discrimination Threshold in Musicians and Non-Musicians

The perception of harmonic complexes provides important information for musical and vocal communication. Numerous studies have shown that musical training and expertise are associated with better processing of harmonic complexes, however, it is unclear whether the perceptual improvement associated with musical training is universal to different pitch models. The current study addresses this issue by measuring discrimination thresholds of musicians (n = 20) and non-musicians (n = 18) to diotic (same sound to both ears) and dichotic (different sounds to each ear) sounds of four stimulus types: (1) pure sinusoidal tones, PT; (2) four-harmonic complex tones, CT; (3) iterated rippled noise, IRN; and (4) interaurally correlated broadband noise, called the "Huggins" or "dichotic" pitch, DP. Frequency difference limens (DLF) for each stimulus type were obtained via a three-alternative-forced-choice adaptive task requiring selection of the interval with the highest pitch, yielding the smallest perceptible fundamental frequency (F0) distance (in Hz) between two sounds. Music skill was measured by an online test of musical pitch, melody and timing maintained by the International Laboratory for Brain Music and Sound Research. Musicianship, length of music experience and self-evaluation of musical skill were assessed by questionnaire. Results showed musicians had smaller DLFs in all four conditions with the largest group difference in the dichotic condition. DLF thresholds were related to both subjective and objective musical ability. In addition, subjective self-report of musical ability was shown to be a significant variable in group classification. Taken together, the results suggest that music-related plasticity benefits multiple mechanisms of pitch encoding and that self-evaluation of musicality can be reliably associated with objective measures of perception.

High-density intracranial recordings reveal a distinct site in anterior dorsal precentral cortex that tracks perceived speech

Various brain regions are implicated in speech processing, and the specific function of some of them is better understood than others. In particular, involvement of the dorsal precentral cortex (dPCC) in speech perception remains debated, and attribution of the function of this region is more or less restricted to motor processing. In this study, we investigated high-density intracranial responses to speech fragments of a feature film, aiming to determine whether dPCC is engaged in perception of continuous speech. Our findings show that dPCC exhibited preference to speech over other tested sounds. Moreover, the identified area was involved in tracking of speech auditory properties including speech spectral envelope, its rhythmic phrasal pattern and pitch contour. DPCC also showed the ability to filter out noise from the perceived speech. Comparing these results to data from motor experiments showed that the identified region had a distinct location in dPCC, anterior to the hand motor area and superior to the mouth articulator region. The present findings uncovered with high-density intracranial recordings help elucidate the functional specialization of PCC and demonstrate the unique role of its anterior dorsal region in continuous speech perception.

A Mathematical Approach to Correlating Objective Spectro-Temporal Features of Non-linguistic Sounds With Their Subjective Perceptions in Humans

Non-linguistic sounds (NLSs) are a core feature of our everyday life and many evoke powerful cognitive and emotional outcomes. The subjective perception of NLSs by humans has occasionally been defined for single percepts, e.g., their pleasantness, whereas many NLSs evoke multiple perceptions. There has also been very limited attempt to determine if NLS perceptions are predicted from objective spectro-temporal features. We therefore examined three human perceptions well-established in previous NLS studies ("Complexity," "Pleasantness," and "Familiarity"), and the accuracy of identification, for a large NLS database and related these four measures to objective spectro-temporal NLS features, defined using rigorous mathematical descriptors including stimulus entropic and algorithmic complexity measures, peaks-related measures, fractal dimension estimates, and various spectral measures (mean spectral centroid, power in discrete frequency ranges, harmonicity, spectral flatness, and spectral structure). We mapped the perceptions to the spectro-temporal measures individually and in combinations, using complex multivariate analyses including principal component analyses and agglomerative hierarchical clustering.

Hierarchical deficits in auditory information processing in schizophrenia

Deficits in auditory processing contribute significantly to impaired functional outcome in schizophrenia (SZ), but mediating factors remain under investigation. Here we evaluated two hierarchical components of early auditory processing: pitch-change detection (i.e. identifying if 2 tones have "same" or "different" pitch), which is preferentially associated with early auditory cortex, and serial pitch-pattern detection (i.e. identifying if 3 tones have "same" or "different" pitch, and, if "different", which one differed from the others), which depends also on auditory association regions. Deficits in pitch-change detection deficits in SZ have been widely reported and correlated with higher auditory disturbances such as Auditory Emotion Recognition (AER). Deficits in serial pitch-pattern discrimination have been less studied. Here, we investigated both pitch perception components, along with integrity of AER in SZ patients vs. controls using behavioral paradigms. We hypothesized that the deficits could be viewed as hierarchically organized in SZ, with deficits in low-level function propagating sequentially through subsequent levels of processing. Participants included 27 SZ and 40 controls. The magnitude of the deficits in SZ participants was large in both the pitch-change (d = 1.15) and serial pitch-pattern tasks (d = 1.21) with no significant differential task effect. The effect size of the AER deficits was extremely large (d = 2.82). In the SZ group, performance in both pitch tasks correlated significantly with impaired AER performance. However, a mediation analysis showed that serial pitch-pattern detection mediated the relationship between simpler pitch-change detection and AER in patients. Findings are consistent with hierarchical models of cognitive dysfunction in SZ with deficits in early information processing contributing to higher level impairments. Furthermore, findings are consistent with recent neurophysiological results suggesting similar level impairments for processing of simple vs. more complex tonal dysfunction in SZ.

Music and Speech Perception in Children Using Sung Speech

This study examined music and speech perception in normal-hearing children with some or no musical training. Thirty children (mean age = 11.3 years), 15 with and 15 without formal music training participated in the study. Music perception was measured using a melodic contour identification (MCI) task; stimuli were a piano sample or sung speech with a fixed timbre (same word for each note) or a mixed timbre (different words for each note). Speech perception was measured in quiet and in steady noise using a matrix-styled sentence recognition task; stimuli were naturally intonated speech or sung speech with a fixed pitch (same note for each word) or a mixed pitch (different notes for each word). Significant musician advantages were observed for MCI and speech in noise but not for speech in quiet. MCI performance was significantly poorer with the mixed timbre stimuli. Speech performance in noise was significantly poorer with the fixed or mixed pitch stimuli than with spoken speech. Across all subjects, age at testing and MCI performance were significantly correlated with speech performance in noise. MCI and speech performance in quiet was significantly poorer for children than for adults from a related study using the same stimuli and tasks; speech performance in noise was significantly poorer for young than for older children. Long-term music training appeared to benefit melodic pitch perception and speech understanding in noise in these pediatric listeners.

Neural representation of octave illusion in the human cortex revealed with functional magnetic resonance imaging

The auditory "octave illusion" arises when dichotic tones, presented one octave apart, alternate rapidly between the ears. This study aimed to explore the link between the perception of illusory pitches and brain activity during presentation of dichotic tones. We conducted a behavioral study of how participants perceived binaural dichotic tones of octave illusions and classified them, based on the reported percepts, in an illusion (ILL) group, without an illusion (non-ILL) group, and others. We recorded brain activity using functional magnetic resonance imaging and analyzed the activation due to dichotic illusion tones. The activation in the bilateral planum polare in the auditory cortex was significantly larger in the ILL group than in the non-ILL group. In the right premotor cortex, the non-ILL group showed a significantly larger activation than did the ILL group, suggesting that the sensation of the meter to the stimulus sound was significant in the non-ILL but not in the ILL group. The results indicated that the activity in these areas was related to the occurrence of octave illusions. The nonsignificant sensation of the meter to the stimulus sound in the ILL group may be consistent with the perception of octave illusion.

Bioelectrical brain effects of one's own voice identification in pitch of voice auditory feedback

Control of voice fundamental frequency (F0) relies in part on comparison of the intended F0 level and auditory feedback. This comparison impacts "sense of agency", or SoA, commonly defined as being the agent of one's own actions and plays a key role for self-awareness and social interactions. SoA is aberrant in several psychiatric disorders. Knowledge about brain activity reflecting SoA can be used in clinical practice for these disorders. It was shown that perception of voice feedback as one's own voice, reflecting the recognition of SoA, alters auditory sensory processing. Using a voice perturbation paradigm we contrasted vocal and bioelectrical brain responses to auditory stimuli that differed in magnitude: 100 and 400 cents. Results suggest the different magnitudes were perceived as a pitch error in self-vocalization (100 cents) or as a pitch shift generated externally (400 cents). Vocalizations and neural responses to changes in pitch of self-vocalization were defined as those made to small magnitude pitch-shifts (100 cents) and which did not show differential neural responses to upward versus downward changes in voice pitch auditory feedback. Vocal responses to large magnitude pitch shifts (400 cents) were smaller than those made to small pitch shifts, and neural responses differed according to upwards versus downward changes in pitch. Our results suggest that the presence of SoA for self-produced sounds may modify bioelectrical brain responses reflecting differences in auditory processing of the direction of a pitch shift. We suggest that this modification of bioelectrical response can be used as a biological index of SoA. Possible neuronal mechanisms of this modification of bioelectrical brain response are discussed.

Assessing Music Perception in Young Children: Evidence for and Psychometric Features of the M-Factor

Given the relationship between language acquisition and music processing, musical perception (MP) skills have been proposed as a tool for early diagnosis of speech and language difficulties; therefore, a psychometric instrument is needed to assess music perception in children under 10 years of age, a crucial period in neurodevelopment. We created a set of 80 musical stimuli encompassing seven domains of music perception to inform perception of tonal, atonal, and modal stimuli, in a random sample of 1006 children, 6–13 years of age, equally distributed from first to fifth grades, from 14 schools (38% private schools) in So Paulo State. The underlying model was tested using confirmatory factor analysis. A model encompassing seven orthogonal specific domains (contour, loudness, scale, timbre, duration, pitch, and meter) and one general music perception factor, the “m-factor,” showed excellent fit indices. The m-factor, previously hypothesized in the literature but never formally tested, explains 93% of the reliable variance in measurement, while only 3.9% of the reliable variance could be attributed to the multidimensionality caused by the specific domains. The 80 items showed no differential item functioning based on sex, age, or enrolment in public vs. private school, demonstrating the important psychometric feature of invariance. Like Charles Spearman's g-factor of intelligence, the m-factor is robust and reliable. It provides a convenient measure of auditory stimulus apprehension that does not rely on verbal information, offering a new opportunity to probe biological and psychological relationships with music perception phenomena and the etiologies of speech and language disorders.

Neural correlates of auditory scale illusion

The auditory illusory perception "scale illusion" occurs when ascending and descending musical scale tones are delivered in a dichotic manner, such that the higher or lower tone at each instant is presented alternately to the right and left ears. Resulting tone sequences have a zigzag pitch in one ear and the reversed (zagzig) pitch in the other ear. Most listeners hear illusory smooth pitch sequences of up-down and down-up streams in the two ears separated in higher and lower halves of the scale. Although many behavioral studies have been conducted, how and where in the brain the illusory percept is formed have not been elucidated. In this study, we conducted functional magnetic resonance imaging using sequential tones that induced scale illusion (ILL) and those that mimicked the percept of scale illusion (PCP), and we compared the activation responses evoked by those stimuli by region-of-interest analysis. We examined the effects of adaptation, i.e., the attenuation of response that occurs when close-frequency sounds are repeated, which might interfere with the changes in activation by the illusion process. Results of the activation difference of the two stimuli, measured at varied tempi of tone presentation, in the superior temporal auditory cortex were not explained by adaptation. Instead, excess activation of the ILL stimulus from the PCP stimulus at moderate tempi (83 and 126 bpm) was significant in the posterior auditory cortex with rightward superiority, while significant prefrontal activation was dominant at the highest tempo (245 bpm). We suggest that the area of the planum temporale posterior to the primary auditory cortex is mainly involved in the illusion formation, and that the illusion-related process is strongly dependent on the rate of tone presentation.

Frequency characteristics of neuromagnetic auditory steady-state responses to sinusoidally amplitude-modulated sweep tones

OBJECTIVE

This study aimed to capture the neuronal frequency characteristics, as indexed by the auditory steady-state response (ASSR), relative to physical characteristics of constant sound pressure levels (SPLs). Relationship with perceptual characteristics (loudness model) was also examined.

METHODS

Neuromagnetic 40-Hz ASSR was recorded in response to sinusoidally amplitude-modulated sweep tones with carrier frequency covering the frequency range of 0.1-12.5kHz. Sound intensity was equalized at 50-, 60-, and 70-dB SPL with an accuracy of ±0.5-dB SPL at the phasic peak of the modulation frequency. Corresponding loudness characteristics were modeled by substituting the detected individual hearing thresholds into a standard formula (ISO226:2003(E)).

RESULTS

The strength of the ASSR component was maximum at 0.5kHz, and it decreased linearly on logarithmic scale toward lower and higher frequencies. Loudness model was plateaued between 0.5 and 4kHz.

CONCLUSIONS

Frequency characteristics of the ASSR were not equivalent to those of SPL and loudness model. Factors other than physical and perceptual frequency characteristics may contribute to characterizing the ASSR.

SIGNIFICANCE

The results contribute to the discussion of the most efficient signal summation for the generation of the ASSR at 0.5kHz and efficient neuronal processing at higher frequencies, which require less energy to retain equal perception.

Functional changes in the human auditory cortex in ageing

Hearing loss, presbycusis, is one of the most common sensory declines in the ageing population. Presbycusis is characterised by a deterioration in the processing of temporal sound features as well as a decline in speech perception, thus indicating a possible central component. With the aim to explore the central component of presbycusis, we studied the function of the auditory cortex by functional MRI in two groups of elderly subjects (>65 years) and compared the results with young subjects (<lt;30 years). The elderly group with expressed presbycusis (EP) differed from the elderly group with mild presbycusis (MP) in hearing thresholds measured by pure tone audiometry, presence and amplitudes of transient otoacoustic emissions (TEOAE) and distortion-product oto-acoustic emissions (DPOAE), as well as in speech-understanding under noisy conditions. Acoustically evoked activity (pink noise centered around 350 Hz, 700 Hz, 1.5 kHz, 3 kHz, 8 kHz), recorded by BOLD fMRI from an area centered on Heschl’s gyrus, was used to determine age-related changes at the level of the auditory cortex. The fMRI showed only minimal activation in response to the 8 kHz stimulation, despite the fact that all subjects heard the stimulus. Both elderly groups showed greater activation in response to acoustical stimuli in the temporal lobes in comparison with young subjects. In addition, activation in the right temporal lobe was more expressed than in the left temporal lobe in both elderly groups, whereas in the young control subjects (YC) leftward lateralization was present. No statistically significant differences in activation of the auditory cortex were found between the MP and EP groups. The greater extent of cortical activation in elderly subjects in comparison with young subjects, with an asymmetry towards the right side, may serve as a compensatory mechanism for the impaired processing of auditory information appearing as a consequence of ageing.

Temporal evolution of neural activity underlying auditory discrimination of frequency increase and decrease

Discriminating a direction of frequency change is an important ability of the human auditory system, although temporal dynamics of neural activity underlying this discrimination remains unclear. In the present study, we recorded auditory-evoked potentials when human subjects explicitly judged a direction of a relative frequency change between two successive tones. A comparison of two types of trials with ascending and descending tone pairs revealed that neural activity discriminating a direction of frequency changes appeared as early as the P1 component of auditory-evoked potentials (latency 50 ms). Those differences between the ascending and descending trials were also observed in subsequent electroencephalographic components such as the N1 (100 ms) and P2 (200 ms). Furthermore, amplitudes of the P2 were significantly modulated by behavioral responses (upward/downward judgments) of subjects in the direction discrimination task, while those of the P1 were not. Those results indicate that, while the neural responses encoding a direction of frequency changes can be observed in an early component of electroencephalographic responses (50 ms after the change), the activity associated (correlated) with behavioral judgments evolves over time, being shaped in a later time period (around 200 ms) of the auditory processing.

Effects of chronic noise exposure on speech-in-noise perception in the presence of normal audiometry

Objective:

To assess auditory processing in noise-exposed subjects with normal audiograms and compare the findings with those of non-noise-exposed normal controls.

Methods:

Ten noise-exposed Royal Air Force aircrew pilots were compared with 10 Royal Air Force administrators who had no history of noise exposure. Participants were matched in terms of age and sex. The subjects were assessed in terms of: pure tone audiometry, transient evoked otoacoustic emissions, suppression of transient evoked otoacoustic emissions in contralateral noise and auditory processing task performance (i.e. masking, frequency discrimination, auditory attention and speech-in-noise).

Results:

All subjects had normal pure tone audiometry and transient evoked otoacoustic emissions amplitudes in both ears. The noise-exposed aircrew had similar pure tone audiometry thresholds to controls, but right ear transient evoked otoacoustic emissions were larger and speech-in-noise thresholds were elevated in the noise-exposed subjects compared to controls.

Conclusion:

The finding of poorer speech-in-noise perception may reflect noise-related impairment of auditory processing in retrocochlear pathways. Audiometry may not detect early, significant noise-induced hearing impairment.

Non-invasive brain stimulation applied to Heschl's gyrus modulates pitch discrimination

The neural basis of the human brain's ability to discriminate pitch has been investigated by functional neuroimaging and the study of lesioned brains, indicating the critical importance of right and left Heschl's gyrus (HG) in pitch perception. Nonetheless, there remains some uncertainty with regard to localization and lateralization of pitch discrimination, partly because neuroimaging results do not allow us to draw inferences about the causality. To address the problem of causality in pitch discrimination functions, we used transcranial direct current stimulation to downregulate (via cathodal stimulation) and upregulate (via anodal stimulation) excitability in either left or right auditory cortex and measured the effect on performance in a pitch discrimination task in comparison with sham stimulation. Cathodal stimulation of HG on the left and on the right hemispheres adversely affected pitch discrimination in comparison to sham stimulation, with the effect on the right being significantly stronger than on the left. Anodal stimulation on either side had no effect on performance in comparison to sham. Our results indicate that both left and right HG are causally involved in pitch discrimination, although the right auditory cortex might be a stronger contributor.

Audiotactile interactions in temporal perception

In the present review, we focus on how commonalities in the ontogenetic development of the auditory and tactile sensory systems may inform the interplay between these signals in the temporal domain. In particular, we describe the results of behavioral studies that have investigated temporal resolution (in temporal order, synchrony/asynchrony, and simultaneity judgment tasks), as well as temporal numerosity perception, and similarities in the perception of frequency across touch and hearing. The evidence reviewed here highlights features of audiotactile temporal perception that are distinctive from those seen for other pairings of sensory modalities. For instance, audiotactile interactions are characterized in certain tasks (e.g., temporal numerosity judgments) by a more balanced reciprocal influence than are other modality pairings. Moreover, relative spatial position plays a different role in the temporal order and temporal recalibration processes for audiotactile stimulus pairings than for other modality pairings. The effect exerted by both the spatial arrangement of stimuli and attention on temporal order judgments is described. Moreover, a number of audiotactile interactions occurring during sensory-motor synchronization are highlighted. We also look at the audiotactile perception of rhythm and how it may be affected by musical training. The differences emerging from this body of research highlight the need for more extensive investigation into audiotactile temporal interactions. We conclude with a brief overview of some of the key issues deserving of further research in this area.

Intensive language training and attention modulate the involvement of fronto-parietal regions during a non-verbal auditory discrimination task

This event-related functional magnetic resonance imaging (fMRI) study was designed in such a manner so as to contribute to the present debate on behavioural and functional transfer effects associated with intensive language training. To address this novel issue, we measured professional simultaneous interpreters and control subjects while they performed a non-verbal auditory discrimination task that primarily relies on attention and categorization functions. The fMRI results revealed that the discrimination of the target stimuli was associated with differential blood oxygen level-dependent responses in fronto-parietal regions between the two groups, even though in-scanner behavioural results did not show significant group differences. These findings are in line with previous observations showing the contribution of fronto-parietal regions to auditory attention and categorization functions. Our results imply that language training modulates brain activity in regions involved in the top-down regulation of auditory functions.

Rate maintenance and resonance in the entorhinal cortex

Throughout the brain, neurons encode information in fundamental units of spikes. Each spike represents the combined thresholding of synaptic inputs and intrinsic neuronal dynamics. Here, we address a basic question of spike train formation: how do perithreshold synaptic inputs perturb the output of a spiking neuron? We recorded from single entorhinal principal cells in vitro and drove them to spike steadily at ∼5 Hz (theta range) with direct current injection, then used a dynamic-clamp to superimpose strong excitatory conductance inputs at varying rates. Neurons spiked most reliably when the input rate matched the intrinsic neuronal firing rate. We also found a striking tendency of neurons to preserve their rates and coefficients of variation, independently of input rates. As mechanisms for this rate maintenance, we show that the efficacy of the conductance inputs varied with the relationship of input rate to neuronal firing rate, and with the arrival time of the input within the natural period. Using a novel method of spike classification, we developed a minimal Markov model that reproduced the measured statistics of the output spike trains and thus allowed us to identify and compare contributions to the rate maintenance and resonance. We suggest that the strength of rate maintenance may be used as a new categorization scheme for neuronal response and note that individual intrinsic spiking mechanisms may play a significant role in forming the rhythmic spike trains of activated neurons; in the entorhinal cortex, individual pacemakers may dominate production of the regional theta rhythm.

Common carp (Cyprinus carpio) response to two pieces of music ("Eine Kleine Nachtmusik" and "Romanza") combined with light intensity, using recirculating water system

The objective of this study was to further investigate the effects of music on fish physiology, bearing in mind available information regarding the involvement of endogenous and exogenous factors in fish farming. Therefore, Cyprinus carpio (50.5 +/- 0.36 g) were reared in a recirculating water system under 80 and 200 lux and subjected to no music at all (control, ambient noise only), 4 h of Mozart's "Eine Kleine Nachtmusik", or 4 h of anonymous "Romanza-Jeux Interdits" for 106 days. Both music treatments resulted in increased growth performance at both light intensities, with Romanza treatment at 200 lux resulting in better growth performance than Mozart treatment. Furthermore, feed efficiency for the Romanza groups was significantly better than for the control. Although no significant music effect was apparent for brain neurotransmitters, lower anterior intestine alkaline protease levels were detected for both music treatments. Taking into consideration the numerous advantages of recirculating water systems, it should be emphasised that fish response to music expresses the results of various physiological and biochemical processes, especially when fish notably respond differently when subjected to two different pieces of music.

Sensitivity and selectivity of neurons in auditory cortex to the pitch, timbre, and location of sounds

We are able to rapidly recognize and localize the many sounds in our environment. We can describe any of these sounds in terms of various independent "features" such as their loudness, pitch, or position in space. However, we still know surprisingly little about how neurons in the auditory brain, specifically the auditory cortex, might form representations of these perceptual characteristics from the information that the ear provides about sound acoustics. In this article, the authors examine evidence that the auditory cortex is necessary for processing the pitch, timbre, and location of sounds, and document how neurons across multiple auditory cortical fields might represent these as trains of action potentials. They conclude by asking whether neurons in different regions of the auditory cortex might not be simply sensitive to each of these three sound features but whether they might be selective for one of them. The few studies that have examined neural sensitivity to multiple sound attributes provide only limited support for neural selectivity within auditory cortex. Providing an explanation of the neural basis of feature invariance is thus one of the major challenges to sensory neuroscience obtaining the ultimate goal of understanding how neural firing patterns in the brain give rise to perception.

Cortical encoding of pitch: recent results and open questions

It is widely appreciated that the key predictor of the pitch of a sound is its periodicity. Neural structures which support pitch perception must therefore be able to reflect the repetition rate of a sound, but this alone is not sufficient. Since pitch is a psychoacoustic property, a putative cortical code for pitch must also be able to account for the relationship between the amount to which a sound is periodic (i.e. its temporal regularity) and the perceived pitch salience, as well as limits in our ability to detect pitch changes or to discriminate rising from falling pitch. Pitch codes must also be robust in the presence of nuisance variables such as loudness or timbre. Here, we review a large body of work on the cortical basis of pitch perception, which illustrates that the distribution of cortical processes that give rise to pitch perception is likely to depend on both the acoustical features and functional relevance of a sound. While previous studies have greatly advanced our understanding, we highlight several open questions regarding the neural basis of pitch perception. These questions can begin to be addressed through a cooperation of investigative efforts across species and experimental techniques, and, critically, by examining the responses of single neurons in behaving animals.

Modulation of auditory evoked responses to spectral and temporal changes by behavioral discrimination training

Background

Due to auditory experience, musicians have better auditory expertise than non-musicians. An increased neocortical activity during auditory oddball stimulation was observed in different studies for musicians and for non-musicians after discrimination training. This suggests a modification of synaptic strength among simultaneously active neurons due to the training. We used amplitude-modulated tones (AM) presented in an oddball sequence and manipulated their carrier or modulation frequencies. We investigated non-musicians in order to see if behavioral discrimination training could modify the neocortical activity generated by change detection of AM tone attributes (carrier or modulation frequency). Cortical evoked responses like N1 and mismatch negativity (MMN) triggered by sound changes were recorded by a whole head magnetoencephalographic system (MEG). We investigated (i) how the auditory cortex reacts to pitch difference (in carrier frequency) and changes in temporal features (modulation frequency) of AM tones and (ii) how discrimination training modulates the neuronal activity reflecting the transient auditory responses generated in the auditory cortex.

Results

The results showed that, additionally to an improvement of the behavioral discrimination performance, discrimination training of carrier frequency changes significantly modulates the MMN and N1 response amplitudes after the training. This process was accompanied by an attention switch to the deviant stimulus after the training procedure identified by the occurrence of a P3a component. In contrast, the training in discrimination of modulation frequency was not sufficient to improve the behavioral discrimination performance and to alternate the cortical response (MMN) to the modulation frequency change. The N1 amplitude, however, showed significant increase after and one week after the training. Similar to the training in carrier frequency discrimination, a long lasting involuntary attention to the deviant stimulus was observed.

Conclusion

We found that discrimination training differentially modulates the cortical responses to pitch changes and to envelope fluctuation changes of AM tones. This suggests that discrimination between AM tones requires additional neuronal mechanisms compared to discrimination process between pure tones. After the training, the subjects demonstrated an involuntary attention switch to the deviant stimulus (represented by the P3a-component in the MEG) even though attention was not prerequisite.

Widespread auditory deficits in tune deafness

OBJECTIVE

The goal of this study was to investigate auditory function in individuals with deficits in musical pitch perception. We hypothesized that such individuals have deficits in nonspeech areas of auditory processing.

DESIGN

We screened 865 randomly selected individuals to identify those who scored poorly on the Distorted Tunes test (DTT), a measure of musical pitch recognition ability. Those who scored poorly were given a comprehensive audiologic examination, and those with hearing loss or other confounding audiologic factors were excluded from further testing. Thirty-five individuals with tune deafness constituted the experimental group. Thirty-four individuals with normal hearing and normal DTT scores, matched for age, gender, handedness, and education, and without overt or reported psychiatric disorders made up the normal control group. Individual and group performance for pure-tone frequency discrimination at 1000 Hz was determined by measuring the difference limen for frequency (DLF). Auditory processing abilities were assessed using tests of pitch pattern recognition, duration pattern recognition, and auditory gap detection. In addition, we evaluated both attention and short- and long-term memory as variables that might influence performance on our experimental measures. Differences between groups were evaluated statistically using Wilcoxon nonparametric tests and t-tests as appropriate.

RESULTS

The DLF at 1000 Hz in the group with tune deafness was significantly larger than that of the normal control group. However, approximately one-third of participants with tune deafness had DLFs within the range of performance observed in the control group. Many individuals with tune deafness also displayed a high degree of variability in their intertrial frequency discrimination performance that could not be explained by deficits in memory or attention. Pitch and duration pattern discrimination and auditory gap-detection ability were significantly poorer in the group with tune deafness than the normal control group. Approximately one-third of our participants with tune deafness displayed evidence of attention deficit with hyperactivity disorder on the Test of Variables of Attention. Test of Variables of Attention scores were significantly correlated with gap-detection scores, but not significantly correlated with any of the other experimental measures, including the DTT, DLF, and auditory pattern discrimination tests. Short- and long-term memory was not significantly related to any of the experimental measures.

CONCLUSIONS

Individuals with tune deafness identified by the DTT have poor performance on many tests of auditory function. These include pure-tone frequency discrimination, pitch and duration pattern discrimination, and temporal resolution. Overall, reduction in performance does not seem to derive from deficits in memory or attention. However, because of the prevalence of attention deficit with hyperactivity disorder in those with tune deafness, this variable should be considered as a potentially confounding factor in future studies of tune deafness and its characteristics. Pure-tone frequency discrimination varied widely in individuals with tune deafness, and the high degree of intertrial variability suggests that frequency discrimination may be unstable in tune-deaf individuals.

Habilidades auditivas e desenvolvimento de linguagem em crianças

TEMA: relação entre anemia e desenvolvimento. OBJETIVO: comparar o desenvolvimento auditivo e de linguagem de crianças anêmicas e não anêmicas entre três e seis anos de idade de uma creche pública de Belo Horizonte. MÉTODO: estudo transversal do tipo caso e controle unicego. Foi realizada punção digital em todas crianças para detecção da anemia (hemoglobina = 11,3g/dL). O grupo caso foi constituído de 19 crianças anêmicas e o controle, de 38 crianças saudáveis, selecionadas por amostragem aleatória pareada. A audição das crianças foi avaliada com emissões otoacústicas, imitanciometria e avaliação simplificada do processamento auditivo. O desenvolvimento de linguagem de cada participante foi observado, utilizando o roteiro de observação de comportamentos de crianças de zero a seis anos. Foram criados índices de desempenho para qualificar as respostas de linguagem das crianças. RESULTADOS: os grupos não diferiram quanto à idade, gênero, aleitamento materno e escolaridade materna. As seguintes variáveis apresentaram diferenças estatisticamente significantes: valores de hemoglobina (10,6g/dL, 12,6g/dL); presença do reflexo acústico (63%, 92%); índices de desempenho de recepção (72,8 - 90,1), emissão (50,6 - 80,6) e aspectos cognitivos da linguagem (47,8 - 76,0) nas crianças anêmicas e não anêmicas, respectivamente. As habilidades auditivas de ordenação temporal para sons verbais e não verbais e localização sonora mostraram-se inadequadas em grande parte das crianças, especialmente, as anêmicas. CONCLUSÕES: as crianças anêmicas diferiram estatisticamente das crianças não anêmicas no que diz respeito às alterações do reflexo acústico e dos índices de desempenho de linguagem, e apresentaram maior prevalência de alterações na avaliação auditiva periférica.

Music perception, pitch, and the auditory system

The perception of music depends on many culture-specific factors, but is also constrained by properties of the auditory system. This has been best characterized for those aspects of music that involve pitch. Pitch sequences are heard in terms of relative as well as absolute pitch. Pitch combinations give rise to emergent properties not present in the component notes. In this review we discuss the basic auditory mechanisms contributing to these and other perceptual effects in music.

Enhanced frequency discrimination in hearing-impaired individuals: A review of perceptual correlates of central neural plasticity induced by cochlear damage

Cochlear damages have been shown to induce changes in tonotopic maps in the central auditory system of animals; neurons deprived from peripheral inputs start to respond to stimuli with frequencies close to the cutoff frequency (Fc) or "edge" of the hearing loss, which then become over-represented at the neural level. Here, we review findings, which reveal a possible psychophysical correlate of such central over-representation in human listeners with sensorineural hearing loss. These findings concur to demonstrate a local improvement in difference limens for frequency (DLFs) at or near Fc. This effect has now been observed in several studies and subjects with varied audiometric characteristics, including high- and low-frequency, and symmetric and asymmetric hearing losses. The presence of cochlear dead region or a steeply sloping hearing loss appear as a necessary condition for its occurrence. The effect cannot be explained simply by more prominent loudness cues or spontaneous otoacoustic emissions (SOAEs) near the audiogram edge. Overall, the data are consistent with local changes in pitch discrimination performance near the hearing-loss cutoff frequency being a result of the neural over-representation of that frequency region in the central auditory system. Further work is needed to confirm this hypothesis, and investigate other possible perceptual correlates of injury-related cortical plasticity in both humans and animals.