Audiovisual spatial ventriloquism is reduced in musicians.

There is great scientific and public interest in claims that musical training improves general cognitive and perceptual abilities. While this is controversial, recent and rather convincing evidence suggests that musical training refines the temporal integration of auditory and visual stimuli at a general level. We investigated whether musical training also affects integration in the spatial domain, via an auditory localisation experiment that measured ventriloquism (where localisation is biased towards visual stimuli on audiovisual trials) and recalibration (a unimodal localisation aftereffect). While musicians (n = 22) and non-musicians (n = 22) did not have significantly different unimodal precision or accuracy, musicians were significantly less susceptible than non-musicians to ventriloquism, with large effect sizes. We replicated these results in another experiment with an independent sample of 24 musicians and 21 non-musicians. Across both experiments, spatial recalibration did not significantly differ between the groups even though musicians resisted ventriloquism. Our results suggest that the multisensory expertise afforded by musical training refines spatial integration, a process that underpins multisensory perception.

Randomizing spectral cues used to resolve front-back reversals in sound-source localization.

Front-back reversals (FBRs) in sound-source localization tasks due to cone-of-confusion errors on the azimuth plane occur with some regularity, and their occurrence is listener-dependent. There are fewer FBRs for wideband, high-frequency sounds than for low-frequency sounds presumably because the sources of low-frequency sounds are localized on the basis of interaural differences (interaural time and level differences), which can lead to ambiguous responses. Spectral cues can aid in determining sound-source locations for wideband, high-frequency sounds, and such spectral cues do not lead to ambiguous responses. However, to what extent spectral features might aid sound-source localization is still not known. This paper explores conditions in which the spectral profile of two-octave wide noise bands, whose sources were localized on the azimuth plane, were randomly varied. The experiment demonstrated that such spectral profile randomization increased FBRs for high-frequency noise bands, presumably because whatever spectral features are used for sound-source localization were no longer as useful for resolving FBRs, and listeners relied on interaural differences for sound-source localization, which led to response ambiguities. Additionally, head rotation decreased FBRs in all cases, even when FBRs increased due to spectral profile randomization. In all cases, the occurrence of FBRs was listener-dependent.

Interaural frequency mismatch jointly modulates neural brainstem binaural interaction and behavioral interaural time difference sensitivity in humans.

The binaural interaction component (BIC) of the auditory brainstem response (ABR) is the difference obtained after subtracting the sum of right and left ear ABRs from binaurally evoked ABRs. The BIC has attracted interest as a biomarker of binaural processing abilities. Best binaural processing is presumed to require spectrally-matched inputs at the two ears, but peripheral pathology and/or impacts of hearing devices can lead to mismatched inputs. Such mismatching can degrade behavioral sensitivity to interaural time difference (ITD) cues, but might be detected using the BIC. Here, we examine the effect of interaural frequency mismatch (IFM) on BIC and behavioral ITD sensitivity in audiometrically normal adult human subjects (both sexes). Binaural and monaural ABRs were recorded and BICs computed from subjects in response to narrowband tones. Left ear stimuli were fixed at 4000 Hz while right ear stimuli varied over a ∼2-octave range (re: 4000 Hz). Separately, subjects performed psychophysical lateralization tasks using the same stimuli to determine ITD discrimination thresholds jointly as a function of IFM and sound level. Results demonstrated significant effects of IFM on BIC amplitudes, with lower amplitudes in mismatched conditions than frequency-matched. Behavioral ITD discrimination thresholds were elevated at mismatched frequencies and lower sound levels, but also more sharply modulated by IFM at lower sound levels. Combinations of ITD, IFM and overall sound level that resulted in fused and lateralized percepts were bound by the empirically-measured BIC, and also by model predictions simulated using an established computational model of the brainstem circuit thought to generate the BIC.

Medial-lateral organization of primary auditory cortex and the question of sound localization.

Pandya made many important contributions to the understanding of the anatomy of the cortical auditory pathways beginning with his publication in 1969. This review focuses on the observation in that article on the transcallosal connections of the primary auditory cortex. The medial part of the cortex has such connections, but the lateral part does not. Pandya and colleagues speculated that this might have something to do with spatial localization of sound. Review of the subsequent literature shows that the primary auditory cortex anatomy is complex, but the original observation is likely correct. However, the physiological speculation was not.

Auditory cortical responses to abrupt lateralization shifts do not reflect the activity of hemifield-specific units involved in opponent coding of auditory space.

Recent studies show that the classical model based on axonal delay-lines may not explain interaural time difference (ITD) based spatial coding in humans. Instead, a population-code model called "opponent channels model" (OCM) has been suggested. This model comprises two competing channels respectively for the two auditory hemifields, each with a sigmoidal tuning curve. Event-related potentials (ERPs) to ITD-changes are used in some studies to test the predictions of this model by considering the sounds before and after the change as adaptor and probe stimuli, respectively. It is assumed in these studies that the former stimulus causes adaptation of the neurons selective to its side, and that the ERP N1-P2 response to the ITD-change is the specific response of the neurons with selectivity to the side of probe sound. However, these ERP components are known as a global, non-specific acoustic change complex of cortical origin evoked by any change in the auditory environment. It probably does not genuinely reflect the activity of some stimulus-specific neuronal units that have escaped the refractory effect of the preceding adaptor, which means a violation of the crucial assumption in an adaptor-probe paradigm. To assess this viewpoint, we conducted two experiments. In the first one, we recorded ERPs to abrupt lateralization shifts of click trains having various pre- and post-shift ITDs within the physiological range of -600µs to +600µs. Magnitudes of the ERP components P1, N1, and P2 to these ITD-shifts did not comply with the additive behavior of partial probe responses presumed for an adaptor-probe paradigm, casting doubt on the accuracy of testing sensory coding models by using ERPs to abrupt lateralization changes. Findings of the second experiment, involving ERPs to conjoint outwards/transverse shift stimuli also supported this conclusion.

Selective attention sharpens population receptive fields in human auditory cortex.

Selective attention enables the preferential processing of relevant stimulus aspects. Invasive animal studies have shown that attending a sound feature rapidly modifies neuronal tuning throughout the auditory cortex. Human neuroimaging studies have reported enhanced auditory cortical responses with selective attention. To date, it remains unclear how the results obtained with functional magnetic resonance imaging (fMRI) in humans relate to the electrophysiological findings in animal models. Here we aim to narrow the gap between animal and human research by combining a selective attention task similar in design to those used in animal electrophysiology with high spatial resolution ultra-high field fMRI at 7 Tesla. Specifically, human participants perform a detection task, whereas the probability of target occurrence varies with sound frequency. Contrary to previous fMRI studies, we show that selective attention resulted in population receptive field sharpening, and consequently reduced responses, at the attended sound frequencies. The difference between our results to those of previous fMRI studies supports the notion that the influence of selective attention on auditory cortex is diverse and may depend on context, stimulus, and task.

Left frontal eye field encodes sound locations during passive listening.

Previous studies reported that auditory cortices (AC) were mostly activated by sounds coming from the contralateral hemifield. As a result, sound locations could be encoded by integrating opposite activations from both sides of AC ("opponent hemifield coding"). However, human auditory "where" pathway also includes a series of parietal and prefrontal regions. It was unknown how sound locations were represented in those high-level regions during passive listening. Here, we investigated the neural representation of sound locations in high-level regions by voxel-level tuning analysis, regions-of-interest-level (ROI-level) laterality analysis, and ROI-level multivariate pattern analysis. Functional magnetic resonance imaging data were collected while participants listened passively to sounds from various horizontal locations. We found that opponent hemifield coding of sound locations not only existed in AC, but also spanned over intraparietal sulcus, superior parietal lobule, and frontal eye field (FEF). Furthermore, multivariate pattern representation of sound locations in both hemifields could be observed in left AC, right AC, and left FEF. Overall, our results demonstrate that left FEF, a high-level region along the auditory "where" pathway, encodes sound locations during passive listening in two ways: a univariate opponent hemifield activation representation and a multivariate full-field activation pattern representation.

Detection of dynamic changes in interaural delay by older adults (L).

The ability of older adults (48 to 72) with relatively intact low-frequency hearing to detect the motion of an acoustic source was investigated using dynamically varying interaural delays. Thresholds were measured using a single-interval two-alternative forced-choice task in which listeners determined if the sound source was moving or stationary. Motion thresholds were significantly larger than stationary localization thresholds. No correlation was observed between age and motion-detection ability for the age range tested. An interesting finding was that there were similar thresholds for older and younger adults. Results suggest reliance on dominant low-frequency binaural timing cues unaffected by high-frequency hearing loss in older adults.

The Relationship Between Interaural Insertion-Depth Differences, Scalar Location, and Interaural Time-Difference Processing in Adult Bilateral Cochlear-Implant Listeners.

Sensitivity to interaural time differences (ITDs) in acoustic hearing involves comparison of interaurally frequency-matched inputs. Bilateral cochlear-implant arrays are, however, only approximately aligned in angular insertion depth and scalar location across the cochleae. Interaural place-of-stimulation mismatch therefore has the potential to impact binaural perception. ITD left-right discrimination thresholds were examined in 23 postlingually-deafened adult bilateral cochlear-implant listeners, using low-rate constant-amplitude pulse trains presented via direct stimulation to single electrodes in each ear. Angular insertion depth and scalar location measured from computed-tomography (CT) scans were used to quantify interaural mismatch, and their association with binaural performance was assessed. Number-matched electrodes displayed a median interaural insertion-depth mismatch of 18° and generally yielded best or near-best ITD discrimination thresholds. Two listeners whose discrimination thresholds did not show this pattern were confirmed via CT to have atypical array placement. Listeners with more number-matched electrode pairs located in the scala tympani displayed better thresholds than listeners with fewer such pairs. ITD tuning curves as a function of interaural electrode separation were broad; bandwidths at twice the threshold minimum averaged 10.5 electrodes (equivalent to 5.9 mm for a Cochlear-brand pre-curved array). Larger angular insertion-depth differences were associated with wider bandwidths. Wide ITD tuning curve bandwidths appear to be a product of both monopolar stimulation and angular insertion-depth mismatch. Cases of good ITD sensitivity with very wide bandwidths suggest that precise matching of insertion depth is not critical for discrimination thresholds. Further prioritizing scala tympani location at implantation should, however, benefit ITD sensitivity.

Discrimination thresholds for interaural-time differences and interaural-level differences in naïve listeners: Sex differences and learning.

The two primary cues to sound-source location on the horizontal plane are interaural time differences (ITDs) and interaural level differences (ILDs). Here we asked whether the ability to discriminate small changes in each of these interaural cues differs between the sexes. We tested one group of males (n = 43) and females (n = 94) on ITD discrimination at 0.5 kHz and a separate group of males (n = 80) and females (n = 166) on ILD discrimination at 4 kHz. None of the participants had any prior experience with psychoacoustic tasks. Testing of each participant was completed in a single testing session of 4-5 blocks of 60 trials. For ILD discrimination, the overall mean threshold, as well as the mean threshold for each block, was statistically significantly lower for males than for females. Despite that, males and females learned at an equal rate over the course of testing. For ITD discrimination, in contrast, thresholds did not differ significantly between the sexes for the overall mean or for any block. There also was no statistically significant learning across blocks for either sex. For both tasks and both sexes, the individual thresholds spanned a wide range. The presence of a statistically significant sex difference and learning for ILD but not for ITD discrimination, along with a larger effect size for ILD than for ITD discrimination, suggests that the factors responsible for these outcomes acted upon an ILD-specific neural pathway, and not upon an ITD-specific pathway, nor any pathway common to the two cues. Because the ILD and ITD specific pathways are most separable initially, the factors associated with sex and learning may have acted upon the ILD-specific pathway at an early stage.

The Development of Sound Localization Latency in Infants and Young Children with Normal Hearing.

With the advances in eye tracking, saccadic reflexes towards auditory stimuli have become an easily accessible behavioral response. The present study investigated the development of horizontal sound localization latency quantified by saccadic reflexes in infants and young children with normal hearing (0.55 to 5.6 years, n = 22). The subject was seated in front of an array of 12 loudspeaker/display-pairs arranged equidistantly in an arc from -55 to + 55° azimuth. An ongoing auditory-visual stimulus was presented at 63 dB SPL and shifted to another randomly selected pair at 24 occasions. At each shift, the visual part of the stimulus was blanked for 1.6 s providing auditory-only localization cues. A sigmoid model was fitted to the gaze samples following the azimuthal sound shifts. The overall sound localization latency (SLL) for a subject was defined as the mean of the latencies for all trials included by objective criteria. The SLL was assessed in 21 of 22 children with a mean of 6.1 valid trials. The SLL ranged 400 to 1400 ms (mean = 860 ms). An inverse model demonstrated a significant relationship between SLL and age (R2 = 0.79, p < 0.001), reflecting a distinct reduction of latency with increasing age. No partial correlation between SLL and sound localization accuracy was found when controlling for age (p = 0.5), suggesting that localization latency may provide diagnostic value beyond accuracy.

Sound source localization patterns and bilateral cochlear implants: Age at onset of deafness effects.

The ability to determine a sound's location is critical in everyday life. However, sound source localization is severely compromised for patients with hearing loss who receive bilateral cochlear implants (BiCIs). Several patient factors relate to poorer performance in listeners with BiCIs, associated with auditory deprivation, experience, and age. Critically, characteristic errors are made by patients with BiCIs (e.g., medial responses at lateral target locations), and the relationship between patient factors and the type of errors made by patients has seldom been investigated across individuals. In the present study, several different types of analysis were used to understand localization errors and their relationship with patient-dependent factors (selected based on their robustness of prediction). Binaural hearing experience is required for developing accurate localization skills, auditory deprivation is associated with degradation of the auditory periphery, and aging leads to poorer temporal resolution. Therefore, it was hypothesized that earlier onsets of deafness would be associated with poorer localization acuity and longer periods without BiCI stimulation or older age would lead to greater amounts of variability in localization responses. A novel machine learning approach was introduced to characterize the types of errors made by listeners with BiCIs, making them simple to interpret and generalizable to everyday experience. Sound localization performance was measured in 48 listeners with BiCIs using pink noise trains presented in free-field. Our results suggest that older age at testing and earlier onset of deafness are associated with greater average error, particularly for sound sources near the center of the head, consistent with previous research. The machine learning analysis revealed that variability of localization responses tended to be greater for individuals with earlier compared to later onsets of deafness. These results suggest that early bilateral hearing is essential for best sound source localization outcomes in listeners with BiCIs.

Effects of sound source localization of masking sound on perception level of simulated tinnitus.

Tinnitus therapies have been combined with the use of varieties of sound/noise. For masking external sounds, location of the masker in space is important; however, effects of the spatial location of the masker on tinnitus are less understood. We aimed to test whether a masking sound location would affect the perception level of simulated tinnitus. The 4 kHz simulated tinnitus was induced in the right ear of healthy volunteers through an open-type earphone. White noise was presented to the right ear using a single-sided headphone or a speaker positioned on the right side at a distance of 1.8 m for masking the simulated tinnitus. In other sessions, monaurally recorded noise localized within the head (inside-head noise) or binaurally recorded noise localized outside the head (outside-head noise) was separately presented from a dual-sided headphone. The noise presented from a distant speaker and the outside-head noise masked the simulated tinnitus in 71.1% and 77.1% of measurements at a lower intensity compared to the noise beside the ear and the inside-head noise, respectively. In conclusion, spatial information regarding the masking noise may play a role in reducing the perception level of simulated tinnitus. Binaurally recorded sounds may be beneficial for an acoustic therapy of tinnitus.

Audiovisual training rapidly reduces potentially hazardous perceptual errors caused by earplugs.

Our ears capture sound from all directions but do not encode directional information explicitly. Instead, subtle acoustic features associated with unique sound source locations must be learned through experience. Surprisingly, aspects of this mapping process remain highly plastic throughout adulthood: Adult human listeners can accommodate acutely modified acoustic inputs ("new ears") over a period of a few weeks to recover near-normal sound localization, and this process can be accelerated with explicit training. Here we evaluated the extent of such plasticity given only transient exposure to distorted inputs. Distortions were produced via earplugs, which severely degrade sound localization performance, constraining their usability in real-world settings that require accurate directional hearing. Localization was measured over a period of ten weeks. Provision of feedback via simple paired auditory and visual stimuli led to a rapid decrease in the occurrence of large errors (responses >|±30°| from target) despite only once-weekly exposure to the altered inputs. Moreover, training effects generalized to untrained sound source locations. Lesser but qualitatively similar improvements were observed in a group of subjects that did not receive explicit feedback. In total, data demonstrate that even transient exposure to altered spatial acoustic information is sufficient for meaningful perceptual improvement (i.e., chronic exposure is not required), offering insight on the nature and time course of perceptual learning in the context of spatial hearing. Data also suggest that the large and potentially hazardous errors in localization caused by earplugs can be mitigated with appropriate training, offering a practical means to increase their usability.

Barn Owl's Auditory Space Map Activity Matching Conditions for a Population Vector Readout to Drive Adaptive Sound-Localizing Behavior.

Space-specific neurons in the owl's midbrain form a neural map of auditory space, which supports sound-orienting behavior. Previous work proposed that a population vector (PV) readout of this map, implementing statistical inference, predicts the owl's sound localization behavior. This model also predicts the frontal localization bias normally observed and how sound-localizing behavior changes when the signal-to-noise ratio varies, based on the spread of activity across the map. However, the actual distribution of population activity and whether this pattern is consistent with premises of the PV readout model on a trial-by-trial basis remains unknown. To answer these questions, we investigated whether the population response profile across the midbrain map in the optic tectum of the barn owl matches these predictions using in vivo multielectrode array recordings. We found that response profiles of recorded subpopulations are sufficient for estimating the stimulus interaural time difference using responses from single trials. Furthermore, this decoder matches the expected differences in trial-by-trial variability and frontal bias between stimulus conditions of low and high signal-to-noise ratio. These results support the hypothesis that a PV readout of the midbrain map can mediate statistical inference in sound-localizing behavior of barn owls.SIGNIFICANCE STATEMENT While the tuning of single neurons in the owl's midbrain map of auditory space has been considered predictive of the highly specialized sound-localizing behavior of this species, response properties across the population remain largely unknown. For the first time, this study analyzed the spread of population responses across the map using multielectrode recordings and how it changes with signal-to-noise ratio. The observed responses support the hypothesis concerning the ability of a population vector readout to predict biases in orienting behaviors and mediate uncertainty-dependent behavioral commands. The results are of significance for understanding potential mechanisms for the implementation of optimal behavioral commands across species.

Effects of temporal fine structure preservation on spatial hearing in bilateral cochlear implant users.

Typically, the coding strategies of cochlear implant audio processors discard acoustic temporal fine structure information (TFS), which may be related to the poor perception of interaural time differences (ITDs) and the resulting reduced spatial hearing capabilities compared to normal-hearing individuals. This study aimed to investigate to what extent bilateral cochlear implant (BiCI) recipients can exploit ITD cues provided by a TFS preserving coding strategy (FS4) in a series of sound field spatial hearing tests. As a baseline, we assessed the sensitivity to ITDs and binaural beats of 12 BiCI subjects with a coding strategy disregarding fine structure (HDCIS) and the FS4 strategy. For 250 Hz pure-tone stimuli but not for broadband noise, the BiCI users had significantly improved ITD discrimination using the FS4 strategy. In the binaural beat detection task and the broadband sound localization, spatial discrimination, and tracking tasks, no significant differences between the two tested coding strategies were observed. These results suggest that ITD sensitivity did not generalize to broadband stimuli or sound field spatial hearing tests, suggesting that it would not be useful for real-world listening.

Transmission of Binaural Cues by Bilateral Cochlear Implants: Examining the Impacts of Bilaterally Independent Spectral Peak-Picking, Pulse Timing, and Compression.

Acoustic hearing listeners use binaural cues-interaural time differences (ITDs) and interaural level differences (ILDs)-for localization and segregation of sound sources in the horizontal plane. Cochlear implant users now often receive two implants (bilateral cochlear implants [BiCIs]) rather than one, with the goal to provide access to these cues. However, BiCI listeners often experience difficulty with binaural tasks. Most BiCIs use independent sound processors at each ear; it has often been suggested that such independence may degrade the transmission of binaural cues, particularly ITDs. Here, we report empirical measurements of binaural cue transmission via BiCIs implementing a common "n-of-m" spectral peak-picking stimulation strategy. Measurements were completed for speech and nonspeech stimuli presented to an acoustic manikin "fitted" with BiCI sound processors. Electric outputs from the BiCIs and acoustic outputs from the manikin's in-ear microphones were recorded simultaneously, enabling comparison of electric and acoustic binaural cues. For source locations away from the midline, BiCI binaural cues, particularly envelope ITD cues, were found to be degraded by asymmetric spectral peak-picking. In addition, pulse amplitude saturation due to nonlinear level mapping yielded smaller ILDs at higher presentation levels. Finally, while individual pulses conveyed a spurious "drifting" ITD, consistent with independent left and right processor clocks, such variation was not evident in transmitted envelope ITDs. Results point to avenues for improvement of BiCI technology and may prove useful in the interpretation of BiCI spatial hearing outcomes reported in prior and future studies.

Human click-based echolocation: Effects of blindness and age, and real-life implications in a 10-week training program.

Understanding the factors that determine if a person can successfully learn a novel sensory skill is essential for understanding how the brain adapts to change, and for providing rehabilitative support for people with sensory loss. We report a training study investigating the effects of blindness and age on the learning of a complex auditory skill: click-based echolocation. Blind and sighted participants of various ages (21-79 yrs; median blind: 45 yrs; median sighted: 26 yrs) trained in 20 sessions over the course of 10 weeks in various practical and virtual navigation tasks. Blind participants also took part in a 3-month follow up survey assessing the effects of the training on their daily life. We found that both sighted and blind people improved considerably on all measures, and in some cases performed comparatively to expert echolocators at the end of training. Somewhat surprisingly, sighted people performed better than those who were blind in some cases, although our analyses suggest that this might be better explained by the younger age (or superior binaural hearing) of the sighted group. Importantly, however, neither age nor blindness was a limiting factor in participants' rate of learning (i.e. their difference in performance from the first to the final session) or in their ability to apply their echolocation skills to novel, untrained tasks. Furthermore, in the follow up survey, all participants who were blind reported improved mobility, and 83% reported better independence and wellbeing. Overall, our results suggest that the ability to learn click-based echolocation is not strongly limited by age or level of vision. This has positive implications for the rehabilitation of people with vision loss or in the early stages of progressive vision loss.

Rehabilitation for unilateral deafness - Narrative review comparing a novel bone conduction solution with existing options.

Patients with single sided deafness (SSD) struggle with sound localization and speech in noise. Existing treatment options include contralateral routing of signal (CROS) systems, percutaneous bone conduction hearing devices (BCHDs), passive transcutaneous BCHDs, active BCHDs, and cochlear implants. Implanted devices provide benefits in speech in noise compared to CROS devices. Percutaneous BCHDs transmit sound efficiently but have aesthetic drawbacks and skin complications. Scalp attenuation impacts passive transcutaneous BCHD performance. Active BCHDs overcome these issues and provide benefits for speech in noise. Cochlear implantation is the only existing option that restores binaural input but introduces electrical rather than acoustic stimuli to the deaf ear. Active BCHDs have been designed to maintain efficient sound transmission and avoid chronic skin irritation and cosmetic concerns that may occur with percutaneous BCHDs. Cochlear implantation may be a superior option for recently deafened SSD patients, though this requires further study. The duration of deafness, patient age and comorbidities, and a shared decision-making model among patients, surgeons, and audiologists should be considered in device selection. The aim of this manuscript is to review available devices, discuss surgical considerations for implantable devices, review available published results for speech in noise and sound quality with each device, and provide an overview to guide shared decision making for patients and providers. This review consolidates available literature and reviews experience with a newer active transcutaneous active BCHD available for use in the SSD population.

Provision of interaural time difference information in chronic intracochlear electrical stimulation enhances neural sensitivity to these differences in neonatally deafened cats.

Although performance with bilateral cochlear implants is superior to that with a unilateral implant, bilateral implantees have poor performance in sound localisation and in speech discrimination in noise compared to normal hearing subjects. Studies of the neural processing of interaural time differences (ITDs) in the inferior colliculus (IC) of long-term deaf animals, show substantial degradation compared to that in normal hearing animals. It is not known whether this degradation can be ameliorated by chronic cochlear electrical stimulation, but such amelioration is unlikely to be achieved using current clinical speech processors and cochlear implants, which do not provide good ITD cues. We therefore developed a custom sound processor to deliver salient ITDs for chronic bilateral intra-cochlear electrical stimulation in a cat model of neonatal deafness, to determine if long-term exposure to salient ITDs would prevent degradation of ITD processing. We compared the sensitivity to ITDs in cochlear electrical stimuli of neurons in the IC of cats chronically stimulated with our custom ITD-aware sound processor with sensitivity in acutely deafened cats with normal hearing development and in cats chronically stimulated with a clinical stimulator and sound processor. Animals that experienced stimulation with our custom ITD-aware sound processor had significantly higher neural sensitivity to ITDs than those that received stimulation from clinical sound processors. There was no significant difference between animals received no stimulation and those that received stimulation from clinical sound processors, consistent with findings from clinical cochlear implant users. This result suggests that development and use of clinical ITD-aware sound processing strategies from a young age may promote ITD sensitivity in the clinical population.