Peripheral Auditory Processing Research Articles

Dysfunction of specific auditory fibers impacts cortical oscillations, driving an autism phenotype despite near-normal hearing.

Autism spectrum disorder is discussed in the context of altered neural oscillations and imbalanced cortical excitation-inhibition of cortical origin. We studied here whether developmental changes in peripheral auditory processing, while preserving basic hearing function, lead to altered cortical oscillations. Local field potentials (LFPs) were recorded from auditory, visual, and prefrontal cortices and the hippocampus of BdnfPax2 KO mice. These mice develop an autism-like behavioral phenotype through deletion of BDNF in Pax2+ interneuron precursors, affecting lower brainstem functions, but not frontal brain regions directly. Evoked LFP responses to behaviorally relevant auditory stimuli were weaker in the auditory cortex of BdnfPax2 KOs, connected to maturation deficits of high-spontaneous rate auditory nerve fibers. This was correlated with enhanced spontaneous and induced LFP power, excitation-inhibition imbalance, and dendritic spine immaturity, mirroring autistic phenotypes. Thus, impairments in peripheral high-spontaneous rate fibers alter spike synchrony and subsequently cortical processing relevant for normal communication and behavior.

The Effect of Aging on Auditory Nerve Function: Insights from Intraoperative eCAP Recordings in Cochlear Implant Users.

Advanced age is associated with poorer speech perception outcomes in cochlear implant (CI) users. In an effort to improve our understanding of the basis for this decline, this study focused on the contributions from peripheral auditory processing, using the electrically evoked compound action potential (eCAP). To investigate the effect of aging on intraoperative, suprathreshold eCAP responses (amplitude growth function [AGF] slopes, eCAP maximum amplitudes, and N1 latencies) across the electrode array, in a large cohort of recipients of newer generation devices, who met hearing preservation criteria. Participants of this retrospective study consisted of 113 middle-aged and older CI recipients. Intraoperative eCAP measures consisted of AGF slopes, maximum amplitudes, and N1 latencies at the maximum amplitude. eCAP recordings were obtained at several intracochlear electrodes, which were grouped by electrode location (basal, middle, and apical). There was a moderate to strong association between suprathreshold eCAP measures (eCAP AGF slopes and maximum amplitudes) and age, particularly for basal and middle electrodes. For apical electrodes, correlations between both suprathreshold eCAP measures and age were weak (and for eCAP maximum amplitudes, not statistically significant). N1 latencies at the maximum amplitudes were not associated with age at any electrode location. Results of this study add to a growing body of evidence suggesting that aging may negatively affect suprathreshold eCAP responses, especially in basal and middle cochlear regions. Although it is difficult to separate the effects of aging from those of duration of deafness, both would support recommending early implantation in the clinical setting.

Sex differences in glutamate AMPA receptor subunits mRNA with fast gating kinetics in the mouse cochlea.

Evidence shows that females have increased supra-threshold peripheral auditory processing compared to males. This is indicated by larger auditory brainstem responses (ABR) wave I amplitude, which measures afferent spiral ganglion neuron (SGN)-auditory nerve synchrony. However, the underlying molecular mechanisms of this sex difference are mostly unknown. We sought to elucidate sex differences in ABR wave I amplitude by examining molecular markers known to affect synaptic transmission kinetics. Alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) mediate fast excitatory transmission in mature SGN afferent synapses. Each AMPAR channel is a tetramer composed of GluA2, 3, and 4 subunits (Gria2, 3, and 4 genes), and those lacking GluA2 subunits have larger currents, are calcium-permeable, and have faster gating kinetics. Moreover, alternatively spliced flip and flop isoforms of each AMPAR subunit affect channel kinetics, having faster kinetics those AMPARs containing Gria3 and Gria4 flop isoforms. We hypothesized that SGNs of females have more fast-gating AMPAR subunit mRNA than males, which could contribute to more temporally precise synaptic transmission and increased SGN synchrony. Our data show that the index of Gria3 relative to Gria2 transcripts on SGN was higher in females than males (females: 48%; males: 43%), suggesting that females have more SGNs with higher Gria3 mRNA relative to Gria2. Analysis of the relative abundance of the flip and flop alternatively spliced isoforms showed that females have a 2-fold increase in fast-gating Gria3 flop mRNA, while males have more slow-gating (2.5-fold) of the flip. We propose that Gria3 may in part mediate greater SGN synchrony in females. Significance Statement: Females of multiple vertebrate species, including fish and mammals, have been reported to have enhanced sound-evoked synchrony of afferents in the auditory nerve. However, the underlying molecular mediators of this physiologic sex difference are unknown. Elucidating potential molecular mechanisms related to sex differences in auditory processing is important for maintaining healthy ears and developing potential treatments for hearing loss in both sexes. This study found that females have a 2-fold increase in Gria3 flop mRNA, a fast-gating AMPA-type glutamate receptor subunit. This difference may contribute to greater neural synchrony in the auditory nerve of female mice compared to males, and this sex difference may be conserved in all vertebrates.

Interplay between attention, working memory, and cognition to speech understanding in noise

Speech understanding in noisy environments depends not only on hearing acuity but also on a host of other cognitive skills including attention, working memory, and executive function that support listeners’ ability to segregate, track and attend to a “target” signal while tuning out other unwanted signals. Identifying the cognitive aspects that affect listening outcomes in complex listening environment is critical for interpreting individual variability and understanding the challenges listeners with different cognitive profiles might face during listening in such environments. The latter is important for characterizing the listening deficits in older adults who, in addition to impaired peripheral auditory processing, also tend to exhibit a decline in various cognitive abilities that might affect listening. Here, we present data from a large cohort of younger listeners on various working memory (Reading Span Test), attention (auditory and visual single and dual task), processing (trail making task), executive control (flanker task), inhibition (Stroop task), and speech in noise tests (spatial release from masking using coordinate Response Measure sentences). The relationship between these various attention, working memory, and cognitive components to speech understanding in complex listening environments will be discussed.

Relationship Between Peripheral and Central Auditory Abilities and Iron Deficiency Anemia in Adolescent Girls.

This study evaluated the peripheral hearing and central auditory processing abilities in Indian adolescent girls with iron deficiency anemia (IDA). The participants consisted of 75 adolescent girls with IDA, 50 adolescent girls without IDA, and 50 adolescent boys without IDA. Participants underwent a test battery to evaluate auditory processing and peripheral hearing assessment. In this study, central auditory processing abilities were assessed using Speech Perception in Noise test in Kannada (SPIN-K) and quick speech perception in noise tests in Kannada, dichotic consonant-vowel test, gap detection threshold (GDT), and auditory digit sequencing and auditory digit span tests. Results showed that the hearing thresholds at extremely low and high frequencies (250 and 8000 Hz), although within clinically normal limits, were poorer in girls with IDA than in the control groups. Also, girls with IDA performed poorly in SPIN-K of the right ear, GDT, and auditory backward digit span tests. These subtle auditory deficiencies may be attributed to the compromised blood supply to the central auditory nervous system, as observed in the current study.

Perception of indexical cues in speech by children and adults with and without dyslexia: Regional dialect and gender identification.

Auditory research in developmental dyslexia proposes that deficient auditory processing of speech underlies difficulties with reading and spelling. Focusing predominantly on phonological processing, studies have not yet addressed the role of the speaker-related (indexical) properties of speech that enable the formation of phonological representations. Here, we assess auditory processing of indexical characteristics cueing a speaker's regional dialect and gender to determine whether dyslexia constraints recognition of dialect features and voice gender. Adults and children aged 11-14 years with dyslexia and their age-matched controls responded to 360 unique sentences extracted from spontaneous conversations of 40 speakers. In addition to the original unprocessed speech, there were two focused filtered conditions (using lowpass filtering at 400 Hz and 8-channel noise vocoding) probing listeners' responses to segmental and prosodic cues. Compared with controls, both groups with dyslexia were significantly limited in their abilities to recognize dialect features from either set of cues. The results for gender suggest that their comparatively worse gender recognition in the noise-vocoded condition was possibly related to poor temporal resolution. We propose that the deficient processing of indexical cues by individuals with dyslexia originates in peripheral auditory processes, of which impaired processing of relevant temporal cues in amplitude envelope is a likely candidate.

Frequency selectivity of tonal language native speakers probed by suppression tuning curves of spontaneous otoacoustic emissions

Native acquisition of a tonal language (TL) is related to enhanced abilities of pitch perception and production, compared to non-tonal language (NTL) native speakers. Moreover, differences in brain responses to both linguistically relevant and non-relevant pitch changes have been described in TL native speakers. It is so far unclear to which extent differences are present at the peripheral processing level of the cochlea. To determine possible differences in cochlear frequency selectivity between Asian TL speakers and Caucasian NTL speakers, suppression tuning curves (STCs) of spontaneous otoacoustic emissions (SOAEs) were examined in both groups. By presenting pure tones, SOAE levels were suppressed and STCs were derived. SOAEs with center frequencies higher than 4.5 kHz were recorded only in female TL native speakers, which correlated with better high-frequency tone detection thresholds. The suppression thresholds at the tip of the STC and filter quality coefficient Q10dB did not differ significantly between both language groups. Thus, the characteristics of the STCs of SOAEs do not support the presence of differences in peripheral auditory processing between TL and NTL native speakers.

Loss of inner hair cell ribbon synapses and auditory nerve fiber regression in Cldn14 knockout mice

Proper functioning of the auditory nerve is of critical importance for auditory rehabilitation by cochlear implants. Here we used the Cldn14−/− mouse to study in detail the effects of Claudin 14 loss on auditory synapses and the auditory nerve. Mutations in the tight junction protein Claudin 14 cause autosomal recessive non-syndromic hearing loss (DFNB29) in humans and mice, due to extensive degeneration of outer and inner hair cells. Here we show that massive inner hair cell loss in Cldn14−/− mice starts after the third postnatal week. Immunohistochemical analysis, using presynaptic Ribeye and postsynaptic GluR2 or PSD 95 as markers, revealed the degeneration of full ribbon synapses in inner hair cells from apical cochlear regions already at postnatal day 12 (P12). At P20, significant reduction in number of ribbon synapses has been observed for all cochlear regions and the loss of synaptic ribbons becomes even more prominent in residual inner hair cells from middle and apical cochlear regions at P45, which by then lost more than 40% of all ribbon synapses. In contrast to excessive noise exposure, loss of Claudin 14 does not cause an increase in “orphan” ribbons with no postsynaptic counterpart due to a reduction of postsynaptic structures. Hair cell loss in Cldn14−/− mice is associated with regression of peripheral auditory nerve processes, especially of outer radial fibers, which normally innervate the outer hair cells. The number of spiral ganglion neurons per area, however, was unchanged between the genotypes. Different effects were observed in the cochlear nucleus complex (CNC), the central projection area of the auditory nerve. While the dorsal cochlear nucleus (DCN) showed a significant 19.7% volume reduction, VGLUT-1 input was reduced by 34.4% in the ventral cochlear nucleus (VCN) but not in the DCN of Cldn14−/− mice. Taken together, massive inner hair cell loss starts after the third postnatal week in Cldn14−/− mice, but is preceded by the loss of ribbon synapses, which may be a first sign of an ongoing degeneration process in otherwise morphologically inconspicuously inner hair cells. In addition to the regression of peripheral nerve processes, reduced levels of VGLUT-1 in the VCN of Cldn14−/− mice suggests that Claudin 14 loss does not only cause hair cell loss but also affects peripheral and central connectivity of the auditory nerve.

Forebrain Dopamine System Regulates Inner Ear Auditory Sensitivity to Socially Relevant Acoustic Signals

Dopamine is integral to attentional and motivational processes, but studies are largely restricted to the central nervous system. In mammals [1, 2] and fishes [3, 4], central dopaminergic neurons project to the inner ear and could modulate acoustic signals at the earliest stages of processing. Studies in rodents show dopamine inhibits cochlear afferent neurons and protects against noise-induced acoustic injury [5-10]. However, other functions for inner ear dopamine have not been investigated, and the effect of dopamine on peripheral auditory processing in non-mammalians remains unknown [11, 12]. Insights could be gained by studies conducted in the context of intraspecific acoustic communication. We present evidence from a vocal fish linking reproductive-state-dependent changes in auditory sensitivity with seasonal changes in the dopaminergic efferent system in the saccule, their primary organ of hearing. Plainfin midshipman (Porichthys notatus) migrate from deep-water winter habitats to the intertidal zone in the summer to breed. Nesting males produce nocturnal vocalizations to attract females [13]. Both sexes undergo seasonal enhancement of hearing sensitivity at the level of the hair cell [14-16], increasing the likelihood of detecting conspecific signals [17, 18]. Importantly, reproductive females concurrentlyhave reduced dopaminergic input to the saccule [19]. Here, we show that dopamine decreases saccule auditory sensitivity via a D2-like receptor. Saccule D2a receptor expression is reduced in the summer and correlates with sensitivity within and across seasons. We propose that reproductive-state-dependent changes to the dopaminergic efferent system provide a release of inhibition in the saccule, enhancing peripheral encoding of social-acoustic signals.

Auditory detection and sound source elevation

The spectral profile of a given sound stimulus varies with the spatial location according to the head-related transfer functions (HRTF) at both ears. For narrowband and tonal stimuli at frequencies above approximately 4 kHz, perceived sound source elevation has been shown to depend mainly on stimulus frequency instead of sound source location (e.g., Blauert, Morimoto), and this result has in turn been shown to correlate with spectral features of the HRTF (e.g., Middlebrooks). However, even though the HRTF is important to perceived elevation, listeners do not generally report a perceptual awareness of the spectral filtering that occurs as a result of the HRTF, suggesting that some form of spectral equalization may occur at some level beyond peripheral auditory processing. Therefore, depending on the level at which detection processing occurs, we might expect different detection thresholds for high frequency stimuli presented from different elevations, or, conversely, we might expect them to be the same. We will report data, collected in a soundfield, concerning the interaction, if any, of sound source elevation and auditory masked detection of high frequency stimuli.

Accounting for a wide variety of binaural detection data by combining cross-correlation and signal-detection theory approaches

We will discuss several experimental contexts in which a Theory of Signal Detection (TSD) approach to modeling has yielded successful, straightforward, and intuitively appealing accounts of data concerning binaural auditory processing. The primary focus will be on recently published empirical data and quantitative modeling from our laboratory. Those reports demonstrate that data obtained in binaural detection experiments conducted across the last five decades can be accounted for by combining a signal-detection-based decision variable with a cross-correlation-based model of binaural processing that incorporates stages of peripheral auditory processing. Notably, some of the data obtained in those experiments had, therefore, been “problematic” in that they had remained either theoretically unaccounted for or, at best, had been only accounted for via ad hoc approaches. Key to developing the unified account of those experimental results was the calculation and inclusion of the variability of the interaural co...

The fine-grained statistical structure of speech is congruent with nonlinear peripheral auditory processing

Efficient coding of sensory signals takes advantage of statistical regularities in sensory data. Cochlear filter in mammals are known to reflect the overall statistical structure of speech, in line with the hypothesis that low-level sensory processing provides efficient codes for information contained in natural stimuli. Recently, some efforts have been made to describe this correspondence in more detail. The study of the statistical structure of speech over different acoustic classes demonstrates that frequency selectivity should not be fixed to achieve maximum efficiency. On the other hand, cochlear signal processing is nonlinear as frequency selectivity decreases with sound intensity level. Both effects are greater in the high frequencies. In the present study, these two facts are shown to be consistent in the case of a parametric method based on Gabor dictionaries (Gaussian-modulated sinusoids) and in a simplified setting. A model with fewer constrains is also introduced for future experiments to validate this hypothesis in a more general context.

Effect of auditory verbal working memory training on speech perception in noise in older adults

Background: Older adults exhibit poor speech perception in noise due to poor spectral, temporal and cognitive processing. According to “ease of language understanding model” good working memory capacity is required to compensate for aberration in peripheral auditory processing so that optimum level speech of understanding can be maintained. However, there is no consensus on the effect of enhanced working memory capacity through auditory training on speech perception. Hence, the effect of working memory training on speech perception in noise in older adults needs to be investigated. Objective: To investigate the effect of auditory verbal working memory training on speech perception in noise in older adults. Method: The present study involved a “two groups, nonrandom selection, pre-test, post-test” study design. Twenty-nine normal hearing older adults within the age range of 61-80 years and 14 of them formed the control group, and 15 of them formed an experimental group. In Phase, I of study, working memory ability and speech perception in noise (SNR-50) were assessed in both the groups. In Phase II the participants in the experimental group were trained using working memory training module. In the last phase of the study, working memory, and SNR-50 were reassessed. Then the pre and post-training scores were compared in both groups. Results : Wilcoxon’s signed rank test revealed that working memory training had positive effect on working memory ability and SNR-50. Conclusions: Working memory training can improve working memory capacity which can in turn improve speech perception in noise.

Hearing profile in Egyptian children with attention-deficit hyperactivity disorders

BackgroundAttention-deficit hyperactivity disorder (ADHD) is a common neuropsychiatric syndrome with onset in childhood, most commonly becoming more apparent during the first few years of grade school. The aim of this study is to assess peripheral hearing and central auditory processing as well as cognitive function in 30 children diagnosed with ADHD. Their age ranged from 6 to 16 years (16 males and 14 females) and their IQ of at least 70. All of them were subjected to a basic audiological evaluation, and assessment of auditory brainstem responses, slow vertex response, and P300 waves using the oddball paradigm.ResultsNo significant differences were found between pure tone thresholds and speech audiometry between the study and the control groups. There was a statistically significant increase in auditory brainstem response (ABR) absolute latencies (III and V) and interpeak latencies (I–III and I–V) at both low repetition rate and high repetition rate. Also, an increase in latencies of N1, P2, N2, and P300 latencies was observed with decreased P300 amplitude of the study group compared with the control groups. A significant mild positive correlation was found between P300 and both wave V latency and I–V interpeak latency.ConclusionThe results of this study provide more evidence of central auditory processing involvement in children with ADHD and show the role of ABR and P300 in the management of these children.

The Relationship Between Spectral Modulation Detection and Speech Recognition: Adult Versus Pediatric Cochlear Implant Recipients.

Adult cochlear implant (CI) recipients demonstrate a reliable relationship between spectral modulation detection and speech understanding. Prior studies documenting this relationship have focused on postlingually deafened adult CI recipients—leaving an open question regarding the relationship between spectral resolution and speech understanding for adults and children with prelingual onset of deafness. Here, we report CI performance on the measures of speech recognition and spectral modulation detection for 578 CI recipients including 477 postlingual adults, 65 prelingual adults, and 36 prelingual pediatric CI users. The results demonstrated a significant correlation between spectral modulation detection and various measures of speech understanding for 542 adult CI recipients. For 36 pediatric CI recipients, however, there was no significant correlation between spectral modulation detection and speech understanding in quiet or in noise nor was spectral modulation detection significantly correlated with listener age or age at implantation. These findings suggest that pediatric CI recipients might not depend upon spectral resolution for speech understanding in the same manner as adult CI recipients. It is possible that pediatric CI users are making use of different cues, such as those contained within the temporal envelope, to achieve high levels of speech understanding. Further investigation is warranted to investigate the relationship between spectral and temporal resolution and speech recognition to describe the underlying mechanisms driving peripheral auditory processing in pediatric CI users.

Intelligibility of bandpass filtered speech: The effect of filter types.

Many studies have examined the contribution of different spectral bands to speech intelligibility, measuring recognition scores of filtered speech stimuli. For a given filter bandwidth, the influence of filter properties on such experiments has been studied mainly with respect to transition band slopes. The objective of the present study was to determine whether nominal transition band slope is a sufficient characterization of filter properties. Several types of filters, both finite impulse response and infinite impulse response types were examined in three experiments to determine if details of the transition band behavior, as well as group delay properties, had any influence on recognition scores. The results of a total of 72 participants showed that for 1/3 octave passbands, differences between filters having the same nominal transition band slopes, but of different types, were large and statistically significant. Linearity of phase response, however, did not influence the results. Further experiments using passband widths of 1/2 and 2/3 octaves revealed that only for the latter the difference in recognition scores between filter types ceased to be significant. These results have important implications for studies which involve filtered speech as well as models that employ different types of filters to emulate peripheral auditory processing.

Temporal effects in interaural and sequential level difference perception.

Temporal effects in interaural level difference (ILD) perception are not well understood. While it is often assumed that ILD sensitivity is independent of the temporal stimulus properties, a reduction of ILD sensitivity for stimuli with a high modulation rate has been reported (known under the term binaural adaptation). Experiment 1 compared ILD thresholds and sequential-level-difference (SLD) thresholds using 300-ms bandpass-filtered pulse trains (centered at 4 kHz) with rates of 100, 400, and 800 pulses per second (pps). In contrast to the SLD thresholds, ILD thresholds were elevated at 800 pps, consistent with literature data that had previously been attributed to binaural adaptation. Experiment 2 showed better ILD sensitivity for pulse trains than for pure tones, suggesting that amplitude modulation enhances ILD sensitivity. The present ILD data and binaural adaptation data from the literature were predicted by a model combining well-established auditory periphery front-ends with an interaural comparison stage. The model also accounted for other published ILD data, including target ILD thresholds in diotic forward and backward fringes and ILD thresholds with different amounts of interaural correlation. Overall, a variety of temporal effects in ILD perception, including binaural adaptation, appear to be largely attributable to monaural peripheral auditory processing.

Some Neurocognitive Correlates of Noise-Vocoded Speech Perception in Children With Normal Hearing: A Replication and Extension of ).

Noise-vocoded speech is a valuable research tool for testing experimental hypotheses about the effects of spectral degradation on speech recognition in adults with normal hearing (NH). However, very little research has utilized noise-vocoded speech with children with NH. Earlier studies with children with NH focused primarily on the amount of spectral information needed for speech recognition without assessing the contribution of neurocognitive processes to speech perception and spoken word recognition. In this study, we first replicated the seminal findings reported by ) who investigated effects of lexical density and word frequency on noise-vocoded speech perception in a small group of children with NH. We then extended the research to investigate relations between noise-vocoded speech recognition abilities and five neurocognitive measures: auditory attention (AA) and response set, talker discrimination, and verbal and nonverbal short-term working memory. Thirty-one children with NH between 5 and 13 years of age were assessed on their ability to perceive lexically controlled words in isolation and in sentences that were noise-vocoded to four spectral channels. Children were also administered vocabulary assessments (Peabody Picture Vocabulary test-4th Edition and Expressive Vocabulary test-2nd Edition) and measures of AA (NEPSY AA and response set and a talker discrimination task) and short-term memory (visual digit and symbol spans). Consistent with the findings reported in the original ) study, we found that children perceived noise-vocoded lexically easy words better than lexically hard words. Words in sentences were also recognized better than the same words presented in isolation. No significant correlations were observed between noise-vocoded speech recognition scores and the Peabody Picture Vocabulary test-4th Edition using language quotients to control for age effects. However, children who scored higher on the Expressive Vocabulary test-2nd Edition recognized lexically easy words better than lexically hard words in sentences. Older children perceived noise-vocoded speech better than younger children. Finally, we found that measures of AA and short-term memory capacity were significantly correlated with a child's ability to perceive noise-vocoded isolated words and sentences. First, we successfully replicated the major findings from the ) study. Because familiarity, phonological distinctiveness and lexical competition affect word recognition, these findings provide additional support for the proposal that several foundational elementary neurocognitive processes underlie the perception of spectrally degraded speech. Second, we found strong and significant correlations between performance on neurocognitive measures and children's ability to recognize words and sentences noise-vocoded to four spectral channels. These findings extend earlier research suggesting that perception of spectrally degraded speech reflects early peripheral auditory processes, as well as additional contributions of executive function, specifically, selective attention and short-term memory processes in spoken word recognition. The present findings suggest that AA and short-term memory support robust spoken word recognition in children with NH even under compromised and challenging listening conditions. These results are relevant to research carried out with listeners who have hearing loss, because they are routinely required to encode, process, and understand spectrally degraded acoustic signals.

Connectivity and ultrastructure of dopaminergic innervation of the inner ear and auditory efferent system of a vocal fish.

Dopamine (DA) is a conserved modulator of vertebrate neural circuitry, yet our knowledge of its role in peripheral auditory processing is limited to mammals. The present study combines immunohistochemistry, neural tract tracing, and electron microscopy to investigate the origin and synaptic characteristics of DA fibers innervating the inner ear and the hindbrain auditory efferent nucleus in the plainfin midshipman, a vocal fish that relies upon the detection of mate calls for reproductive success. We identify a DA cell group in the diencephalon as a common source for innervation of both the hindbrain auditory efferent nucleus and saccule, the main hearing endorgan of the inner ear. We show that DA terminals in the saccule contain vesicles but transmitter release appears paracrine in nature, due to the apparent lack of synaptic contacts. In contrast, in the hindbrain, DA terminals form traditional synaptic contacts with auditory efferent neuronal cell bodies and dendrites, as well as unlabeled axon terminals, which, in turn, form inhibitory-like synapses on auditory efferent somata. Our results suggest a distinct functional role for brain-derived DA in the direct and indirect modulation of the peripheral auditory system of a vocal nonmammalian vertebrate.

An interaural-correlation-based approach that accounts for a wide variety of binaural detection data

Interaural cross-correlation-based models of binaural processing have accounted successfully for a wide variety of binaural phenomena, including binaural detection, binaural discrimination, and measures of extents of laterality based on interaural temporal disparities, interaural intensitive disparities, and their combination. This report focuses on quantitative accounts of data obtained from binaural detection experiments published over five decades. Particular emphasis is placed on stimulus contexts for which commonly used correlation-based approaches fail to provide adequate explanations of the data. One such context concerns binaural detection of signals masked by certain noises that are narrow-band and/or interaurally partially correlated. It is shown that a cross-correlation-based model that includes stages of peripheral auditory processing can, when coupled with an appropriate decision variable, account well for a wide variety of classic and recently published binaural detection data including those that have, heretofore, proven to be problematic.