Auditory System Research Articles

Acute Aromatase Inhibition Impairs Neural and Behavioral Auditory Scene Analysis in Zebra Finches.

Auditory perception can be significantly disrupted by noise. To discriminate sounds from noise, auditory scene analysis (ASA) extracts the functionally relevant sounds from acoustic input. The zebra finch communicates in noisy environments. Neurons in their secondary auditory pallial cortex (caudomedial nidopallium, NCM) can encode song from background chorus, or scenes, and this capacity may aid behavioral ASA. Furthermore, song processing is modulated by the rapid synthesis of neuroestrogens when hearing conspecific song. To examine whether neuroestrogens support neural and behavioral ASA in both sexes, we retrodialyzed fadrozole (aromatase inhibitor, FAD) and recorded in vivo awake extracellular NCM responses to songs and scenes. We found that FAD affected neural encoding of songs by decreasing responsiveness and timing reliability in inhibitory (narrow-spiking), but not in excitatory (broad-spiking) neurons. Congruently, FAD decreased neural encoding of songs in scenes for both cell types, particularly in females. Behaviorally, we trained birds using operant conditioning and tested their ability to detect songs in scenes after administering FAD orally or injected bilaterally into NCM. Oral FAD increased response bias and decreased correct rejections in females, but not in males. FAD in NCM did not affect performance. Thus, FAD in the NCM impaired neuronal ASA but that did not lead to behavioral disruption suggesting the existence of resilience or compensatory responses. Moreover, impaired performance after systemic FAD suggests involvement of other aromatase-rich networks outside the auditory pathway in ASA. This work highlights how transient estrogen synthesis disruption can modulate higher-order processing in an animal model of vocal communication.

Auditory-inspired adaptive frequency tracking

One of the best frequency trackers to date is the human (mammalian) auditory system, which has evolved through millions of years of resolving classification problems. It is a versatile, elegant and powerful sound processing unit. It excels in detecting, estimating, and classifying multiple targets simultaneously even in noisy environments. Hence, mimicking even some features of the auditory system could be beneficial in developing superior frequency tracking and classification algorithms. An auditory inspired adaptive synchrony capture filterbank (SCFB) signal processing architecture for tracking signal frequency components was proposed in a related paper [JASA-2013]. The SCFB architecture consists of a fixed array of traditional, passive linear, gammatone filters in cascade with a bank of three adaptively tunable bandpass filters that form a frequency-discriminator-loop (FDL). The SCFB exhibits many desirable properties for processing speech, music, and other complex sounds. In recent work [Dec2021], the algorithm was modified using adaptive tuning parameters, and a generalized way to determine/suppress voiced and unvoiced (silent) regions. This modified algorithm estimates frequencies with higher accuracy even in the presence of closely spaced input tones. Preliminary analysis with synthetic, human speech and humpback/whale-call signals demonstrates that the revised algorithm performs well. This talk will focus on follow-on work.

An introduction to psychological and physiological acoustics

The technical committee on Psychological and Physiological acoustics (P&P) is concerned with a wide and multidisciplinary range of topics. P&P members address questions of how the auditory system transforms and processes incoming sound and how sound is used to facilitate behaviors like communication and navigation. Physiological acoustics concerns topics, such as the mechanical and acoustical mechanisms of the middle and inner ear and neurophysiology of peripheral and central auditory systems. Psychological acoustics concerns, for example, behavioral studies of auditory perception and cognition. Within these topics, research covers the basic science of normal function and hearing disorders, as well as clinical, translational, and applied questions related to hearing aids, cochlear implants, and audio technology. Membership and activities of P&P overlap heavily with several other technical committees in ASA, especially Architectural Acoustics, Animal Bioacoustics, Noise, and Speech Communication. This presentation will feature a brief overview and several examples of P&P research.

Reduced processing efficiency impacts auditory detection of amplitude modulation in children: Evidence from an experimental and modeling study

Auditory detection of the Amplitude Modulation (AM) of sounds, crucial for speech perception, improves until 10 years of age. This protracted development may not only be explained by sensory maturation, but also by improvements in processing efficiency: the ability to make efficient use of available sensory information. This hypothesis was tested behaviorally on 86 6-to-9-year-olds and 15 adults using AM-detection tasks assessing absolute sensitivity, masking, and response consistency in the AM domain. Absolute sensitivity was estimated by the detection thresholds of a sinusoidal AM applied to a pure-tone carrier; AM masking was estimated as the elevation of AM-detection thresholds produced when replacing the pure-tone carrier by a narrowband noise; response consistency was estimated using a double-pass paradigm where the same set of stimuli was presented twice. Results showed that AM sensitivity improved from childhood to adulthood, but did not change between 6 and 9 years. AM masking did not change with age, suggesting that the selectivity of perceptual AM filters was adult-like by 6 years. However, response consistency increased developmentally, supporting the hypothesis of reduced processing efficiency in early childhood. At the group level, double-pass data of children and adults were well simulated by a model of the human auditory system assuming a higher level of internal noise for children. At the individual level, for both children and adults, double-pass data were better simulated when assuming a sub-optimal decision strategy in addition to differences in internal noise. In conclusion, processing efficiency for AM detection is reduced in childhood. Moreover, worse AM detection was linked to both systematic and stochastic inefficiencies, in both children and adults.

Evaluation of efferent influences on neural coding using pre-clinical models of sensorineural hearing loss

The medial olivocochlear (MOC) efferent system is less explored than the ascending auditory pathway but likely contributes in important ways to neural coding and perception. These effects are thought to vary across stimulus configurations, anesthetic states, and subtypes of sensorineural hearing loss (SNHL). To explore effective assays of MOC effects on neural coding, we have recorded Interleaved otoacoustic emissions (OAEs) and envelope following responses (EFRs) from several pre-clinical SNHL chinchilla models. Our preliminary observations include increases in OAEs with inner-hair-cell loss and anesthesia, which may be due to reduced efferent strength. Additionally, we observed enhanced EFRs with an added noise masker, which also could be related to efferent effects. We are using sedated and awake OAE comparisons to develop a standard efferent assay for use in neural-coding studies. Interleaved recording of OAEs and EFRs track cochlear-gain and neural-coding changes during acoustic stimuli. A recently developed modeling framework (Farhadi et al., 2023 JASA) that includes different MOC projection pathways, including midbrain modulation-sensitive inputs, is used to guide most-effective stimulus selection. Ultimately, this model-guided experimental framework will provide unique guidance for testing MOC hypotheses related to neural coding.

Localizing sounds revolving at very high velocities: An auditory wagon-wheel effect

Localizing sound sources as they move around us is a critical function of the auditory system. Yet most research focuses on static sound sources or sources moving at slow velocities. The present work explores circular trajectories at very high velocities well above the velocity at which we lose the sense of direction (∼2.5 rot/s with white noise). As the number of rotations per second approaches the fundamental frequency of the spinning sound, a sense of direction re-emerges. This creates what has been described informally as the auditory equivalent to the wagon-wheel effect: the sound appears to move in one direction when the velocity is below the fundamental frequency, and it appears to move in the opposite direction when the velocity is above the fundamental frequency. We report on two experiments testing this effect with a 200-Hz complex sound using adaptive VBAP spatialization on a 16-loudspeaker array. Experiment 1 (N = 15) confirmed that participants perceived opposite directions when the velocity was below or above the fundamental frequency. Experiment 2 (N = 7) explores the relationship between this effect at very high velocities and the ability to track sound at slower velocities. Preliminary findings suggest some overlap between localization processes at slow and high velocities.

Spatiotemporal expression of AP-2/myosin Ⅵ in mouse cochlear IHCs and correlation with auditory function

Background Recycling of synaptic vesicles plays an important role in vesicle pool replenishment, neurotransmitter release and synaptic plasticity. Clathrin-mediated endocytosis (CME) is considered to be the main mechanism for synaptic vesicle replenishment. AP-2 (adaptor-related protein complex 2) and myosin Ⅵ are known as key proteins that regulate the structure and dynamics of CME. Objective This study aims to reveal the spatiotemporal expression of AP-2/myosin Ⅵ in inner hair cells (IHCs) of the mouse cochlea and its correlation with auditory function. Material and Methods Immunofluorescence was used to detect the localization and expression of AP-2 and myosin Ⅵ in cochlear hair cells (HCs) of CBA/CaJ mice of various ages. qRT-PCR was used to verify the differential expression of AP-2 and myosin Ⅵ mRNA in the mouse cochlea, and ABR tests were administered to mice of various ages. A preliminary analysis of the correlation between AP-2/myosin Ⅵ levels and auditory function was conducted. Results AP-2 was located in the cytoplasmic region of IHCs and was mainly expressed in the basal region of IHCs and the area near ribbon synapses, while myosin Ⅵ was expressed in the cytoplasmic region of IHCs and OHCs. Furthermore, AP-2 and myosin Ⅵ were not significant detected in the cochleae of P7 mice; the expression level reached a peak at P35 and then decreased significantly with age. The expression patterns and expression levels of AP-2 and myosin Ⅵ in the cochleae of the mice were consistent with the development of the auditory system. Conclusions and Significance AP-2 and myosin Ⅵ protein expression may differ in mice of different ages, and this variation probably leads to a difference in the efficiency in CME; it may also cause a defect in IHC function.

Modified rhyme test performance and error patterns predict self-reported frequency of temporary threshold shifts for normal hearing listeners

After exposure to a loud sound, listeners may report that their hearing is dull or muffled. If hearing returns to pre-exposure levels, the change is considered a temporary threshold shift (TTS). TTSs are likely associated with damage to the auditory system. How frequently TTSs are experienced has been shown to be related to performance deficits on tasks like the modified rhyme test (MRT), even if audiometric thresholds are normal. The present study seeks to better understand the types of phonetic errors listeners with different frequencies of TTSs make on the MRT. Over 4000 US Service Members (SMs) completed the study. SMs were asked how frequently they experienced a TTS: “Never,” “Infrequent” ( < 1/year), or “Frequent” (≥1/ year). SMs completed 80 trials of a version of the MRT where SNR and target level were manipulated. Responses were analyzed using information theory and statistical modeling. Overall proportion correct, reaction time, and error rates associated with phonetic features were predictors of TTS frequency for normal hearing listeners. [The views expressed in this abstract are those of the authors and do not necessarily reflect the official policy of the Department of Defense or the U.S. Government.]

Quantifying northern bottlenose and sperm whale acoustic behavioural responses to anthropogenic noise in Baffin Bay, Canada

Marine mammals rely on their auditory system for a myriad of life functions (e.g., navigating, foraging, socializing) and consequently, are vulnerable to loud human activities (e.g., vessel traffic, fishing, military activities). These activities can impede communication, cause behavioural disturbances, and can even cause injuries. As the Arctic warms and sea ice coverage decreases, more opportunities for human activities are arising. How noise impacts the acoustic behaviour of Arctic marine mammals is unclear. In October 2022 and 2023 controlled noise exposure experiments were conducted using military sonar (source level of 176.4 dB re 1 μPa) on northern bottlenose and sperm whales in Baffin Bay while they were foraging around vessels actively fishing. Hydrophone suction-cup biologgers (DTAGs; n = 5, ∼72 cumulative hours) were used to capture vessel and sonar noises, and whale vocalizations before, during, and after the noise exposure periods. Using a click detector, focal whale clicks were identified and quantitatively compared to received noise levels. This information will then be used to determine noise thresholds for acoustical behavioural responses. These results will support risk-mitigation strategies for the Department of National Defence Canada and Fisheries and Oceans Canada, as well as address Inuit concerns about the effects of military sonar on marine mammals.

A Time-Saving Alternative to "Peak-Picking" Algorithms: A Gaussian Mixture Model Feature Extraction Technique for the Neurodiagnostic Auditory Brainstem Response.

The accurate and efficient analysis of neurodiagnostic auditory brainstem responses (ABR) plays a critical role in assessing auditory pathway function in human and animal research and in clinical diagnosis. Traditional analysis of the neurodiagnostic ABR analysis involves visual inspection of the waveform and manually marking peaks and troughs. Visual inspection is a tedious and time-consuming task, especially in research where there may be hundreds or thousands of waveforms to analyze. "Peak-picking" algorithms have made this task faster; however, they are prone to the same errors as visual inspection. A Gaussian mixture model-based feature extraction technique (GMM-FET) is a descriptive model of ABR morphology and an alternative to peak-picking algorithms. The GMM-FET is capable of modeling multiple waves and accounting for wave interactions, compared with other template-matching approaches that fit single waves. The present study is a secondary analysis applying the GMM-FET to 321 ABRs from adult humans from 2 datasets using different stimuli and recording parameters. Goodness-of-fit of the GMM-FET to waves I and V and surrounding waves, that is, the summating potential and waves IV and VI, was assessed, and latency and amplitude estimations by the GMM-FET were compared with estimations from visual inspection. The GMM-FET had a similar success rate to visual inspection in extracting peak latency and amplitude, and there was low RMS error and high intraclass correlation between the model and response waveform. Mean peak latency differences between the GMM-FET and visual inspection were small, suggesting the two methods chose the same peak in the majority of waveforms. The GMM-FET estimated wave I amplitudes within 0.12 µV of visual inspection, but estimated larger wave V amplitudes than visual inspection. The results suggest the GMM-FET is an appropriate method for extracting peak latencies and amplitudes for neurodiagnostic analysis of ABR waves I and V.

Sensorineural hearing loss and cognitive impairment: three hypotheses.

Sensorineural hearing loss (SNHL) is a category of hearing loss that often leads to difficulty in understanding speech and other sounds. Auditory system dysfunction, including deafness and auditory trauma, results in cognitive deficits via neuroplasticity. Cognitive impairment (CI) refers to an abnormality in the brain's higher intellectual processes related to learning, memory, thinking and judgment that can lead to severe learning and memory deficits. Studies have established a strong correlation between SNHL and CI, but it remains unclear how SNHL contributes to CI. The purpose of this article is to describe three hypotheses regarding this relationship, the mainstream cognitive load hypothesis, the co-morbidity hypothesis, and the sensory deprivation hypothesis, as well as the latest research progress related to each hypothesis.

Cochlear Ribbon Synapses in Aged Gerbils.

In mammalian hearing, type-I afferent auditory nerve fibers comprise the basis of the afferent auditory pathway. They are connected to inner hair cells of the cochlea via specialized ribbon synapses. Auditory nerve fibers of different physiological types differ subtly in their synaptic location and morphology. Low-spontaneous-rate auditory nerve fibers typically connect on the modiolar side of the inner hair cell, while high-spontaneous-rate fibers are typically found on the pillar side. In aging and noise-damaged ears, this fine-tuned balance between auditory nerve fiber populations can be disrupted and the functional consequences are currently unclear. Here, using immunofluorescent labeling of presynaptic ribbons and postsynaptic glutamate receptor patches, we investigated changes in synaptic morphology at three different tonotopic locations along the cochlea of aging gerbils compared to those of young adults. Quiet-aged gerbils showed about 20% loss of afferent ribbon synapses. While the loss was random at apical, low-frequency cochlear locations, at the basal, high-frequency location it almost exclusively affected the modiolar-located synapses. The subtle differences in volumes of pre- and postsynaptic elements located on the inner hair cell's modiolar versus pillar side were unaffected by age. This is consistent with known physiology and suggests a predominant, age-related loss in the low-spontaneous-rate auditory nerve population in the cochlear base, but not the apex.

CHD7 and SOX2 act in a common gene regulatory network during mammalian semicircular canal and cochlear development

Inner ear morphogenesis requires tightly regulated epigenetic and transcriptional control of gene expression. CHD7, an ATP-dependent chromodomain helicase DNA-binding protein, and SOX2, an SRY-related HMG box pioneer transcription factor, are known to contribute to vestibular and auditory system development, but their genetic interactions in the ear have not been explored. Here, we analyzed inner ear development and the transcriptional regulatory landscapes in mice with variable dosages of Chd7 and/or Sox2. We show that combined haploinsufficiency for Chd7 and Sox2 results in reduced otic cell proliferation, severe malformations of semicircular canals, and shortened cochleae with ectopic hair cells. Examination of mice with conditional, inducible Chd7 loss by Sox2CreER reveals a critical period (~E9.5) of susceptibility in the inner ear to combined Chd7 and Sox2 loss. Data from genome-wide RNA-sequencing and CUT&Tag studies in the otocyst show that CHD7 regulates Sox2 expression and acts early in a gene regulatory network to control expression of key otic patterning genes, including Pax2 and Otx2. CHD7 and SOX2 directly bind independently and cooperatively at transcription start sites and enhancers to regulate otic progenitor cell gene expression. Together, our findings reveal essential roles for Chd7 and Sox2 in early inner ear development and may be applicable for syndromic and other forms of hearing or balance disorders.

The Auditory Pathway in Congenitally Cytomegalovirus-Infected Human Fetuses.

Congenital cytomegalovirus (CMV) infection is the main cause of non-hereditary sensorineural hearing loss (SNHL). In order to shed light on SNHL pathophysiology, we examined the auditory pathway in CMV-infected fetuses; the temporal lobe, in particular the auditory cortex, and the inner ear. We investigated both inner ears and temporal lobes of 20 human CMV-infected fetuses at 21 weeks of gestation. As a negative group, five fetuses from spontaneous miscarriages without CMV infection were studied. Inner ears and temporal lobes were histologically examined, immunohistochemistry for CMV and CMV-PCR were performed. On the auditory cortex, we evaluated the local microglial reaction to the infection. CMV-positive cells were found in 14/20 brains and the damage was classified as severe, moderate, or mild, according to histological features. Fetuses with severe brain damage had a statistically higher temporal lobe viral load and a higher number of activated microglial cells in the auditory cortex compared to fetuses with mild brain damage (p: 0.01; p: 0.01). In the inner ears, the marginal cells of the stria vascularis were the most CMV positive. In our study, CMV affected the auditory pathway, suggesting a tropism for this route. In addition, in the auditory cortex, microglial activation may favor further tissue damage contributing to hearing loss.

Age-Related Deficits in Binaural Hearing: Contribution of Peripheral and Central Effects.

Pure-tone audiograms often poorly predict elderly humans' ability to communicate in everyday complex acoustic scenes. Binaural processing is crucial for discriminating sound sources in such complex acoustic scenes. The compromised perception of communication signals presented above hearing threshold has been linked to both peripheral and central age-related changes in the auditory system. Investigating young and old Mongolian gerbils of both sexes, an established model for human hearing, we demonstrate age-related supra-threshold deficits in binaural hearing using behavioral, electrophysiological, anatomical, and imaging methods. Binaural processing ability was measured as the binaural masking level difference (BMLD), an established measure in human psychophysics. We tested gerbils behaviorally with "virtual headphones," recorded single-unit responses in the auditory midbrain and evaluated gross midbrain and cortical responses using positron emission tomography (PET) imaging. Furthermore, we obtained additional measures of auditory function based on auditory brainstem responses, auditory-nerve synapse counts, and evidence for central inhibitory processing revealed by PET. BMLD deteriorates already in middle-aged animals having normal audiometric thresholds and is even worse in old animals with hearing loss. The magnitude of auditory brainstem response measures related to auditory-nerve function and binaural processing in the auditory brainstem also deteriorate. Furthermore, central GABAergic inhibition is affected by age. Because the number of synapses in the apical turn of the inner ear was not reduced in middle-aged animals, we conclude that peripheral synaptopathy contributes little to binaural processing deficits. Exploratory analyses suggest increased hearing thresholds, altered binaural processing in the brainstem and changed central GABAergic inhibition as potential contributors.

AUDITORY REHABILIATION DURING THE COVID-19 PANDEMIC – THE PARENTS’ PERSPECTIVE

The Covid-19 pandemic has affected numerous aspects of human existence, thus increasing psychological stress in the overall population worldwide. Healthcare and social support systems have suffered extreme challenges and pressures. The welfare, protection, and rights of socially vulnerable groups, such as children with loss of hearing and their families, were challenged. The system of auditory rehabilitation encountered numerous problems due to the Covid-19 pandemic, because of the compromised access to rehabilitation facilities and therapists. The objective of the study was to investigate the parents’ perspective on the influence of the Covid-19 pandemic on auditory rehabilitation. A questionnaire was developed to gather the parents’ answers to the research questions. The sample consisted of fifty-one parents of deaf children and children hard of hearing enrolled in the auditory rehabilitation process. The results showed a considerable impact of the pandemic on the accessibility of rehabilitation, with periods of two to three months of complete disruption for most children, due to lockdown. A vast number of parents experienced psychological stress due to those changes, accompanied by the fear of contracting Covid-19 when attending rehabilitation facilities. Most of the parents observed changes in their child’s behaviour, and communication difficulties due to face masks during the pandemic. Numerous studies support these findings. The results of our research show that the improvement and an increase in the flexibility of the auditory rehabilitation system are necessary. Auditory rehabilitation should be supported by state-of-the-art technologies (e.g., telecommunication) in order to ensure the continuity of the rehabilitation process and support for hearing-impaired children and their parents, even in extreme circumstances.

Increased reliance on temporal coding when target sound is softer than the background

Everyday environments often contain multiple concurrent sound sources that fluctuate over time. Normally hearing listeners can benefit from high signal-to-noise ratios (SNRs) in energetic dips of temporally fluctuating background sound, a phenomenon called dip-listening. Specialized mechanisms of dip-listening exist across the entire auditory pathway. Both the instantaneous fluctuating and the long-term overall SNR shape dip-listening. An unresolved issue regarding cortical mechanisms of dip-listening is how target perception remains invariant to overall SNR, specifically, across different tone levels with an ongoing fluctuating masker. Equivalent target detection over both positive and negative overall SNRs (SNR invariance) is reliably achieved in highly-trained listeners. Dip-listening is correlated with the ability to resolve temporal fine structure, which involves temporally-varying spike patterns. Thus the current work tests the hypothesis that at negative SNRs, neuronal readout mechanisms need to increasingly rely on decoding strategies based on temporal spike patterns, as opposed to spike count. Recordings from chronically implanted electrode arrays in core auditory cortex of trained and awake Mongolian gerbils that are engaged in a tone detection task in 10 Hz amplitude-modulated background sound reveal that rate-based decoding is not SNR-invariant, whereas temporal coding is informative at both negative and positive SNRs.

Relationship Between Chloroquine or Hydroxychloroquine Use and Hearing Disorders: A Systematic Review and Meta-Analysis.

Chloroquine and its analog hydroxychloroquine are derivatives of 4-aminoquinoline and are regularly used in the treatment of malaria and autoimmune diseases. Among the side effects of these drugs, alterations associated with the auditory system are frequently mentioned. Thus, the aim of this systematic review is to systematically review publications on hearing disorders and chloroquine or hydroxychloroquine use. Inclusion criteria were observational or interventional studies on audiological assessment in participants who were using chloroquine or hydroxychloroquine. The methodological quality was independently assessed by two reviewers using the Meta-Analysis of Statistics: assessment and review Instrument. The certainty of the evidence was assessed using the GRADE tool. A total of 1,372 non-duplicate papers were screened, out of which 17 were included in the final qualitative synthesis, and 5 studies in the meta-analysis. The odds ratio for the two subgroups evaluated did not show significance with no heterogeneity between the effects observed between the different diseases (I2=0%) and obtaining the global estimate of 0.76 (95% confidence interval [CI]=0.41-1.39; p>0.05). Despite the inclusion of papers with different disease samples, the heterogeneity observed in the analysis was low (I2= 0%) and prediction interval (95% PI=0.32-1.80; p>0.05) remained close to that estimated by the CI (95% CI=0.41-1.39; p>0.05). The certainty of the evidence assessed by the GRADE tool was considered very low due to the risk of bias, indirect evidence, and imprecision. The findings of this study suggest that the use of chloroquine/hydroxychloroquine is not associated with hearing disorders.

Sensory Gating in the Auditory System: Classical and Novel Stimulus Paradigms.

Sensory gating is a phenomenon where the cortical response to the second stimulus in a pair of identical stimuli is inhibited. It is most often assessed in a conditioning-testing paradigm. Both active and passive neuronal mechanisms have been implicated in sensory gating. The present study aimed to assess if sensory gating is caused by an active neural mechanism associated with stimulus redundancy. The study was carried out on 20 young neurotypical adults. We assessed the gating phenomenon using identical and nonidentical stimuli pairs presented in an electrophysiological conditioning-testing paradigm. We hypothesized that the novel stimulus in the nonidentical stimulus pair would not exhibit the sensory gating effects (reduction in the amplitude of cortical potentials to the second stimuli in the pair), owing to stimulus novelty. Contrary to our expectations, the response analyses of the cortical auditory evoked potentials revealed that adults gated repetitive and novel stimuli similarly. The findings are discussed in relation to the significance of methodological factors in evaluating sensory gating. We believe that additional research using oddball presentation of novel stimuli along with appropriate analysis methods is necessary before drawing any conclusions on the mechanisms underlying sensory gating.

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.