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Interaural time differences (ITDs) at low frequencies are important for sound localization and spatial speech unmasking. These ITD cues are not encoded in commonly used envelope-based stimulation strategies for cochlear implants (CIs) using high pulse rates. However, ITD sensitivity can be improved by adding extra pulses with short inter-pulse intervals (SIPIs) in unmodulated high-rate trains. Here, we investigated whether this improvement also applies to amplitude-modulated (AM) high-rate pulse trains. To this end, we systematically varied the temporal position of SIPI pulses within the envelope cycle (SIPI phase), the fundamental frequency (F0) of AM (125 Hz and 250 Hz), and AM depth (from 0.1 to 0.9). Stimuli were presented at an interaurally place-matched electrode pair at a reference pulse rate of 1000 pulses/s. Participants performed an ITD-based left/right discrimination task. SIPI insertion resulted in improved ITD sensitivity throughout the range of modulation depths and for both male and female F0s. The improvements were largest for insertion at and around the envelope peak. These results are promising for conveying salient ITD cues at high pulse rates commonly used to encode speech information.

Description, Biased synaptic arrangement facilitates sublinear integration and binaural spatial hearing for low-frequency sound., Clustering of synapses allows neurons to overcome attenuation of electrical signals at dendrites. However, we show in avian binaural coincidence detectors computing interaural time difference for sound localization that clustering of synapses rather promotes the dendritic attenuation but augments the intensity tolerance of the binaural computations. Using glutamate uncaging, we found in the neurons that synapses were clustered at distal dendritic branches. Modeling revealed that this strengthened sublinear integration within a dendritic tree but enabled the integration of signals from different trees when inputs grow stronger, preventing monoaural output and maintaining the dynamic range of binaural computation. The extent of this clustering differed according to dendritic length and frequency tuning of neurons, being most prominent for long dendrites and low-frequency tuning. This ensures binaural spatial hearing for wide intensity and frequency ranges, highlighting the importance of coupling of synapse geometry with dendritic morphology and input frequency in sensory signal processing.

Humans perceive sound lags and differences in loudness between their two ears to ascertain the location of sounds in terms of azimuth, elevation and interval, etc. Humans and animals can determine the direction of sounds using only two ears, by making use of interaural time difference (ITD), interaural phase difference (IPD), interaural intensity difference (IID), etc. Robots can also use sound localization to detect changes in the environment around them; consequently, various sound localization methods for robots have been investigated. Since many animals have two ears, two ears seem to be the minimum requirement for determining sound localization. While most robot’s sound localization systems are based on microphone arrays that consist of three or more microphones, several researchers have attempted achieving binaural sound localization in robots. Nakashima (Nakashima and Mukai, 2004) developed a system that consisted of two microphones with pinnae and a camera that was only utilized in learning. By adopting a neural network that estimated the control command, he proposed a method utilizing sound signals for guiding the robot in the direction of a sound. Takanishi (Takanishi et al., 1993) achieved continuous direction localization of a sound source in the horizontal plane. They used the interaural sound pressure difference and the ONSET time difference as parameters and proposed a method for achieving two-step direction localization in a humanoid head using these parameters. Kumon (Kumon et al., 2003) approached the problem using an adaptive audio servo system based on IID as the control method for orientating the robots in the direction of the sound source in the horizontal plane by using two microphones. This chapter describes the use of an audio servo of elevation for achieving sound localization using spectral cues caused by pinnae. Here, the term “audio servo” denotes a method for simultaneously localizing sound sources and controlling the robot’s configuration, in contrast with conventional methods that are based on the “listen-and-move” principal. The audio servo is characterized by a feedback system that steers the robot toward the direction of the sound by combining dynamic motion of the robot with auditory ability. In order to achieve this, this chapter proposes a method for detecting instantaneous spectral cues, when these cues are not very accurate. Furthermore, controllers that compensate for the inaccuracy of the measured signalare also considered. In addition, this

Purpose Electric and acoustic stimulation (EAS) with preserved hearing in the implanted ear provides benefit for speech understanding, spatial hearing, and quality of life in adults. However, there is limited research on EAS outcomes in children. The aims of this study were to estimate the magnitude of EAS-related benefit on speech understanding in children with preserved acoustic hearing and to determine what role acoustic interaural time difference (ITD) sensitivity may have on said EAS benefit. Methods Six children with acoustic hearing preservation and 20 children with normal hearing (NH) were recruited to participate. Speech recognition was assessed via an eight-loudspeaker array with speech presented from one loudspeaker at 0 degree and restaurant noise from all other loudspeakers (45-315 degrees). ITD thresholds were measured for a 250-Hz signal presented acoustically via insert earphones. Results Only one EAS listener demonstrated significant benefit from bilateral acoustic hearing as compared with acoustic hearing from a single ear. ITD thresholds were poor in the range of 302 to 1000+ ms and were considerably poorer than ITD thresholds for the NH group. Conclusion These data suggest that children with acoustic hearing preservation may not exhibit initial EAS benefit for speech recognition in semi-diffuse noise; however, because none exhibited a decrement in performance with bilateral acoustic stimulation, EAS fittings are recommended to provide binaural acoustic access allowing for EAS adaptation to binaural cues over time. Future research should address the emergence of EAS benefit, binaural cue sensitivity, and the role of EAS experience in children and adults.

We present a biologically inspired sound localisation system for reverberant environments using the Cascade of Asymmetric Resonators with Fast-Acting Compression (CAR-FAC) cochlear model. The system exploits a CAR-FAC pair to pre-process binaural signals that travel through the inherent delay line of the cascade structures, as each filter acts as a delay unit. Following the filtering, each cochlear channel is cross-correlated with all the channels of the other cochlea using a quantised instantaneous correlation function to form a 2-D instantaneous correlation matrix (correlogram). The correlogram contains both interaural time difference and spectral information. The generated correlograms are analysed using a regression neural network for localisation. We investigate the effect of the CAR-FAC nonlinearity on the system performance by comparing it with a CAR only version. To verify that the CAR/CAR-FAC and the quantised instantaneous correlation provide a suitable basis with which to perform sound localisation tasks, a linear regression, an extreme learning machine, and a convolutional neural network are trained to learn the azimuthal angle of the sound source from the correlogram. The system is evaluated using speech data recorded in a reverberant environment. We compare the performance of the linear CAR and nonlinear CAR-FAC models with current sound localisation systems as well as with human performance.

Sound source localization is paramount for comfort of life, determining the position of a sound source in 3 dimensions: azimuth, height and distance. It is based on 3 types of cue: 2 binaural (interaural time difference and interaural level difference) and 1 monaural spectral cue (head-related transfer function). These are complementary and vary according to the acoustic characteristics of the incident sound. The objective of this report is to update the current state of knowledge on the physical basis of spatial sound localization.

In a remote microphone (RM) system, a talker speaks into a microphone and the signal is transmitted to the hearing aids worn by the hearing-impaired listener. A difficulty with remote microphones, however, is that the signal received at the hearing aid bypasses the head and pinna, so the acoustic cues needed to externalize the sound source are missing. The objective of this paper is to process the RM signal to improve externalization when listening through earphones. The processing is based on a structural binaural model, which uses a cascade of processing modules to simulate the interaural level difference, interaural time difference, pinna reflections, ear-canal resonance, and early room reflections. The externalization results for the structural binaural model are compared to a left-right signal blend, the listener's own anechoic head-related impulse response (HRIR), and the listener's own HRIR with room reverberation. The azimuth is varied from straight ahead to 90° to one side. The results show that the structural binaural model is as effective as the listener's own HRIR plus reverberation in producing an externalized acoustic image, and that there is no significant difference in externalization between hearing-impaired and normal-hearing listeners.

Masked detection thresholds were measured for a noise target in the presence of a masker composed of (1) a lead/lag noise pair with the lead interaural time difference (ITD) set the same or opposite to the target, (2) a diotic masker, and (3) a dichotic pair of decorrelated noises. If the precedence effect actually eliminates a second, later arriving stimulus, a spatial release from masking would be expected when the lead ITD is opposite that of the target. Results for a range of lead/lag delays suggest that the precedence effect is not the result of a perceptual removal of the lag.

The morphology of the head and pinna shape the spatial and frequency dependence of sound propagation that give rise to the acoustic cues to sound source location. During early development, the physical dimensions of the head and pinna increase rapidly. Thus, the binaural (interaural time and level differences, ITD and ILD) and monaural (spectral shape) cues are also hypothesized to change rapidly. Complex interactions between the size and shape of the head and pinna limit the accuracy of simple acoustical models (e.g. spherical) and necessitate empirical measurements. Here, we measured the cues to location in the developing guinea pig, a precocial species commonly used for studies of the auditory system. We measured directional transfer functions (DTFs) and the dimensions of the head and pinna in guinea pigs from birth (P0) through adulthood. Dimensions of the head and pinna increased by 87% and 48%, respectively, reaching adult values by ~8 weeks (P56). The monaural acoustic gain produced by the head and pinna increased with frequency and age, with maximum gains at higher frequencies (>8 kHz) reaching values of 10–21 dB for all ages. The center frequency of monaural spectral notches also decreased with age, from higher frequencies (~17 kHz) at P0 to lower frequencies (~12 kHz) in adults. In all animals, ILDs and ITDs were dependent on both frequency and spatial location. Over development, the maximum ILD magnitude increased from ~15 dB at P0 to ~30 dB in adults (at frequencies >8 kHz), while the maximum low frequency ITDs increased from ~185 µs at P0 to ~300 µs in adults. These results demonstrate that the changes in the acoustical cues are directly related to changes in head and pinna morphology.

Sound source localization (SSL) uses interaural time difference (ITD) or interaural intensity difference (IID) cues, and most of the methods based on ITD are limited by the aperture of array. However, a kind of parasitoid fly called Ormia ochracea with coupled ears has a remarkable ability to localize the calling of the host regardless of fly’s small body size. It is believed that the ITD is amplified by the auditory organ of Ormia. This paper proposes a biological coupled sensor array, which is generalized by the structure of Ormia’s ear. The array contains two pairs of microphones with a multistage iteration passive localization algorithm. Four microphones are symmetrically placed on the x- and y- axis of the array respectively. The proposed localization algorithm transforms the received signals to coupled signals by means of coupled calculator. The phase difference between two coupled signals is amplified. The ITD information is achieved based on the generalized cross-correlation function and amended by iteration of the coupled calculator and phase shift operation. To validate the effect of the proposed sensor array, experiments are conducted using sine waves from different angles of incidence. The ITDs between two microphones are amplified as expect. The localization results are achieved with localization error less than 0.5 degree with single-source cases in the experiment. The localization error is reduced by using this biological coupled sensor array with the multistage iteration method.

Speech reception thresholds (SRTs) decrease as target and maskers are spatially separated (spatial release from masking, SRM). The current study systematically assessed how SRTs and SRM for a frontal target in a spatially symmetric masker configuration depend on spectro-temporal masker properties, the availability of short-time interaural level difference (ILD) and interaural time difference (ITD), and informational masking. Maskers ranged from stationary noise to single, interfering talkers and were modified by head-related transfer functions to provide: (i) different binaural cues (ILD, ITD, or both) and (ii) independent maskers in each ear ("infinite ILD"). Additionally, a condition was tested in which only information from short-time spectro-temporal segments of the ear with a favorable signal-to-noise ratio (better-ear glimpses) was presented. For noise-based maskers, ILD, ITD, and spectral changes related to masker location contributed similarly to SRM, while ILD cues played a larger role if temporal modulation was introduced. For speech maskers, glimpsing and perceived location contributed roughly equally and ITD contributed less. The "infinite ILD" condition might suggest better-ear glimpsing limitations resulting in a maximal SRM of 12 dB for maskers with low or absent informational masking. Comparison to binaural model predictions highlighted the importance of short-time processing and helped to clarify the contribution of the different binaural cues and mechanisms.

Previous studies have shown that normal-hearing (NH) listeners' spatial perception of non-stationary interaural time differences (ITDs) is dominated by the carrier ITD during rising amplitude segments. Here, ITD sensitivity throughout the amplitude-modulation cycle in NH listeners and bilateral cochlear implant (CI) subjects is compared, the latter by means of direct stimulation of a single electrode pair. The data indicate that, while NH listeners are most sensitive to ITDs applied toward the beginning of a modulation cycle at 600 Hz, NH listeners at 200 Hz and especially bilateral CI subjects at 200 pulses per second (pps) are more sensitive to ITDs applied to the modulation maximum. This has implications for spatial-hearing in complex environments: NH listeners' dominant 600-Hz ITD information from the rising amplitude segments comprises direct sound information. The 200-pps low rate required to get ITD sensitivity in CI users results in a higher weight of pulses later in the modulation cycle where the source ITDs are more likely corrupted by reflections. This indirectly indicates that even if future binaural CI processors are able to provide perceptually exploitable ITD information, CI users will likely not get the full benefit from such pulse-based ITD cues in reverberant and other complex environments.

Objectives Many bilateral cochlear implant users show sensitivity to binaural information when stimulation is provided using a pair of synchronized electrodes. However, there is large variability in binaural sensitivity between and within participants across stimulation sites in the cochlea. It was hypothesized that within-participant variability in binaural sensitivity is in part affected by limitations and characteristics of the auditory periphery which may be reflected by monaural hearing performance. The objective of this study was to examine the relationship between monaural and binaural hearing performance within participants with bilateral cochlear implants. Design Binaural measures included dichotic signal detection and interaural time difference discrimination thresholds. Diotic signal detection thresholds were also measured. Monaural measures included dynamic range and amplitude modulation detection. In addition, loudness growth was compared between ears. Measures were made at three stimulation sites per listener. Results Greater binaural sensitivity was found with larger dynamic ranges. Poorer interaural time difference discrimination was found with larger difference between comfortable levels of the two ears. In addition, poorer diotic signal detection thresholds were found with larger differences between the dynamic ranges of the two ears. No relationship was found between amplitude modulation detection thresholds or symmetry of loudness growth and the binaural measures. Conclusions The results suggest that some of the variability in binaural hearing performance within listeners across stimulation sites can be explained by factors nonspecific to binaural processing. The results are consistent with the idea that dynamic range and comfortable levels relate to peripheral neural survival and the width of the excitation pattern which could affect the fidelity with which central binaural nuclei process bilateral inputs.

Previous electrophysiological studies of interaural time difference (ITD) processing have demonstrated that ITDs are represented by a nontopographic population rate code. Rather than narrow tuning to ITDs, neural channels have broad tuning to ITDs in either the left or right auditory hemifield, and the relative activity between the channels determines the perceived lateralization of the sound. With advancing age, spatial perception weakens and poor temporal processing contributes to declining spatial acuity. At present, it is unclear whether age-related temporal processing deficits are due to poor inhibitory controls in the auditory system or degraded neural synchrony at the periphery. Cortical processing of spatial cues based on a hemifield code are susceptible to potential age-related physiological changes. We consider two distinct predictions of age-related changes to ITD sensitivity: declines in inhibitory mechanisms would lead to increased excitation and medial shifts to rate-azimuth functions, whereas a general reduction in neural synchrony would lead to reduced excitation and shallower slopes in the rate-azimuth function. The current study tested these possibilities by measuring an evoked response to ITD shifts in a narrow-band noise. Results were more in line with the latter outcome, both from measured latencies and amplitudes of the global field potentials and source-localized waveforms in the left and right auditory cortices. The measured responses for older listeners also tended to have reduced asymmetric distribution of activity in response to ITD shifts, which is consistent with other sensory and cognitive processing models of aging.

International audience; Aim: To evaluate azimuthal sound-source localization performance under different conditions, with a view to optimizing a routine sound localization protocol.Material and method: Two groups of healthy, normal-hearing subjects were tested identically, except that one had to keep their head still while the other was allowed to turn it. Sound localization was tested without and then with a right ear plug (acute auditory asymmetry) for each of the following sound stimuli: pulsed narrow-band centered on 250Hz, continuous narrowband centered on 2000Hz, 4000Hz and 8000Hz, continuous 4000Hz warble, pulsed white noise, and word ("lac" (lake)). Root mean square error was used to calculate sound-source localization accuracy.Results: With fixed head, localization was significantly disturbed by the earplug for all stimuli (P

This paper proposes a 3D acoustic source localization method by the use of a single microphone pair. This is achieved by using Interaural Time Difference (ITD) cues as measured by the microphone pair mounted on a rotating platform to cover the entire scope of the area. The application of the rotating microphone pair is studied for two practical approaches, one using Time Difference of Arrival (TDOA) between the microphone pair corresponding to different rotational angles using Generalized Cross-Correlation method with phase transform weighting function (GCC-PHAT) and the other choosing to maximize source Steered Power Response (SPR) at the output of a delay and sum (DAS) beamformer. The main purpose of this paper is to study the implementation of this technique for search and rescue robots to locate live survivors trapped under rubble, as a replacement or supplement to radar, optical and infrared based life detection methods. The paper concludes with suggested future improvements to the model.

Relative motion between the body and the outside world is a rich source of information. Neural selectivity to motion is well-established in several sensory systems, but is controversial in hearing. This study examines neural sensitivity to changes in the instantaneous interaural time difference of sounds at the two ears. Midbrain neurons track such changes up to extremely high speeds, show only a coarse dependence of firing rate on speed, and lack directional selectivity. These results argue against the presence of selectivity to auditory motion at the level of the midbrain, but reveal an acuity which enables coding of fast-fluctuating binaural cues in realistic sound environments. no ISSN ispartof: The Journal of the Acoustical Society of America Express Letters vol:145 issue:1 pages:EL45-EL51 ispartof: location:United States status: published

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.

Sound source localization uses interaural time difference (ITD) or interaural intensity difference cues, and most of the methods based on ITD are limited by the aperture of array. However, a kind of parasitoid fly called Ormia ochracea with coupled ears has a remarkable ability to localize calling of crickets regardless of the fly's small body size. The structure of fly's ear is generalized, and a multi-dimensional coupled system with an acoustic sensor array is proposed. The magnification factor of the phase difference in this system, which can be used to describe the ITD changes of signals from the coupled system, is chosen as the kernel parameter to measure the effect of coupling. The coupled system is optimized by choosing appropriate physical parameters such that the degree of magnification does not vary with angle of incidence. The simulation results demonstrate that the time delay between two signals increases by the coupled system, and the magnification factor remains stable as expected. Compared with the traditional general cross-correlation method, the localization error of the coupled system is reduced.

Spatial judgments are often dominated by low-frequency binaural cues and onset cues when binaural cues vary across the spectrum and duration, respectively, of a brief sound. This study combined these dimensions to assess the spectrotemporal weighting of binaural information. Listeners discriminated target interaural time difference (ITD) and interaural level difference (ILD) carried by the onset, offset, or full duration of a 4-kHz Gabor click train with a 2-ms period in the presence or absence of a diotic 500-Hz interferer tone. ITD and ILD thresholds were significantly elevated by the interferer in all conditions and by a similar amount to previous reports for static cues. Binaural interference was dramatically greater for ITD targets lacking onset cues compared to onset and full-duration conditions. Binaural interference for ILD targets was similar across dynamic-cue conditions. These effects mirror the baseline discriminability of dynamic ITD and ILD cues [Stecker and Brown. (2010). J. Acoust. Soc. Am. 127, 3092–3103], consistent with stronger interference for less-robust/higher-variance cues. The results support the view that binaural cue integration occurs simultaneously across multiple variance-weighted dimensions, including time and frequency.

Traditional methods often only use monaural masking models to decorrelate input signals for stereo acoustic echo cancellation. Whereas, it seems more reasonable to use binaural masking models for the following two reasons. First, stereo signals are heard by two ears rather than just one. Second, psychoacoustic researchers have already shown that there are obvious masking level differences between binaural masking models and monaural masking models. By studying binaural masking level difference models, we first introduce a simplified binaural masking model for stereo acoustic echo cancellation. Considering that the interaural time difference is dominant at low frequencies ( ⩽ 1.5 kHz) and the interaural level difference is a major cue at higher frequencies, we propose to use different signal decorrelation schemes at these two frequency bands. In the low-frequency band, a pitch-driven sinusoidal injection scheme is proposed to maintain the interaural time difference, where the amount of injection is determined by the proposed binaural masking model. In the high-frequency band, a modified sinusoidal phase modulation scheme is applied to make a trade-off between preserving the interaural level difference and decorrelating the stereophonic input signals. Assessment results show that the proposed method can effectively improve the non-unique problem and retain good speech quality.

The ability of normal-hearing (NH) listeners to exploit interaural time difference (ITD) cues conveyed in the modulated envelopes of high-frequency sounds is poor compared to ITD cues transmitted in the temporal fine structure at low frequencies. Sensitivity to envelope ITDs is further degraded when envelopes become less steep, when modulation depth is reduced, and when envelopes become less similar between the ears, common factors when listening in reverberant environments. The vulnerability of envelope ITDs is particularly problematic for cochlear implant (CI) users, as they rely on information conveyed by slowly varying amplitude envelopes. Here, an approach to improve access to envelope ITDs for CIs is described in which, rather than attempting to reduce reverberation, the perceptual saliency of cues relating to the source is increased by selectively sharpening peaks in the amplitude envelope judged to contain reliable ITDs. Performance of the algorithm with room reverberation was assessed through simulating listening with bilateral CIs in headphone experiments with NH listeners. Relative to simulated standard CI processing, stimuli processed with the algorithm generated lower ITD discrimination thresholds and increased extents of laterality. Depending on parameterization, intelligibility was unchanged or somewhat reduced. The algorithm has the potential to improve spatial listening with CIs.

A precedence effect model is described that can use a binaural signal to robustly localize a sound source in the presence of multiple reflections for the frontal horizontal plane. The model also estimates a room impulse response from a running binaural signal and determines the spatial locations and delays of early reflections, without any prior or additional knowledge of the source. A dual-layer cross-correlation/auto-correlation algorithm is used to determine the interaural time difference of the direct sound source component and to estimate a binaural activity pattern.

Sound-source localization in the horizontal plane relies on detecting small differences in the timing and level of the sound at the two ears, including differences in the timing of the modulated envelopes of high-frequency sounds (envelope interaural time differences (ITDs)). We investigated responses of single neurons in the inferior colliculus (IC) to a wide range of envelope ITDs and stimulus envelope shapes. By a novel means of visualizing neural activity relative to different portions of the periodic stimulus envelope at each ear, we demonstrate the role of neuron-specific excitatory and inhibitory inputs in creating ITD sensitivity (or the lack of it) depending on the specific shape of the stimulus envelope. The underlying binaural brain circuitry and synaptic parameters were modeled individually for each neuron to account for neuron-specific activity patterns. The model explains the effects of envelope shapes on sensitivity to envelope ITDs observed in both normal-hearing listeners and in neural data, and has consequences for understanding how ITD information in stimulus envelopes might be maximized in users of bilateral cochlear implants-for whom ITDs conveyed in the stimulus envelope are the only ITD cues available.

The roles of interaural time difference (ITD) and interaural level difference (ILD) were studied in free-field source localization experiments for sine tones of low frequency (250-750 Hz). Experiments combined real-source trials with virtual trials created through transaural synthesis based on real-time ear canal measurements. Experiments showed the following: (1) The naturally occurring ILD is physically large enough to exert an influence on sound localization well below 1000 Hz. (2) An ILD having the same sign as the ITD modestly enhances the perceived azimuth of tones for all values of the ITD, and it eliminates left-right confusions that otherwise occur when the interaural phase difference (IPD) passes 180°. (3) Increasing the ILD to large, implausible values can decrease the perceived laterality while also increasing front-back confusions. (4) Tone localization is more directly related to the ITD than to the IPD. (5) An ILD having a sign opposite to the ITD promotes a slipped-cycle ITD, sometimes with dramatic effects on localization. Because the role of the ITD itself is altered by the ILD, the duplex processing of ITD and ILD reflects more than mere trading; the effect of the ITD can be reversed in sign.

A temporally acute binaural system can help to resolve inherent fluctuations in binaural information that are often present in complex auditory scenes. Using a broadband noise stimulus that rapidly alternates between two different values of interaural time difference (ITD), the ability of the binaural system to hear the lateral position resulting from one of the ITD values was investigated. Results show that listeners are able to accurately lateralize brief noise tokens of only 3-7 ms in duration. In two subsequent experiments, the role of an amplitude modulation (AM) imposed on the ITD-switching stimulus used in the first experiment was tested. For wideband stimuli, the temporal position of the ITD target relative to the phase of the AM did not influence absolute lateralization or detection performance. When the stimuli were narrowband, however, detection of the ITD target was best when temporally positioned in the rising portion of the AM. These experiments illustrate that the auditory system is capable of making accurate lateral estimates of very brief moments of ITD information. Furthermore, for these instantaneous changes in ITD information, the stimulus bandwidth can influence the role of envelope cues for the readout of binaural information.

The majority of everyday listening situations involve a complex mixture of multiple sound sources. Assuming a spectro-temporally sparse target signal, e.g., speech, the binaural cues in these complex listening environments do not simply result from a single sound source, but are often rapidly switching between the most dominant sources at any given moment. To investigate the perception of rapidly switching interaural time difference (ITD) cues, a noise stimulus that periodically alternates between two different values of ITD was created. This stimulus appears to evoke a purely binaural percept of modulation, which is the focus of the studies presented here. Results indicate that listeners can reliably discriminate this ITD-switching stimulus from a stimulus composed of stationary ITD cues. Frequency discrimination of this ITD-switching stimulus was tested in a separate experiment, which showed that listeners are generally able to discriminate a 50% change in modulation frequency for reference rates below 16 Hz. The final study investigated if modulation masking exists between the monaural and binaural auditory pathways. Although a statistically significant increase in modulation detection thresholds was observed when both types of modulations were presented together, the increase was relatively small, indicating only a weak interaction.

With the development of multichannel sound with height, it is desirable to create a virtual source in different vertical directions, especially in the vertical plane of the frontal hemisphere. For this purpose, a local Ambisonics panning method is proposed in the present work. In this analysis, three loudspeakers are arranged in different elevations, with one located in the horizontal plane and other two located at 30° ~ 45° above or below the horizontal plane, respectively. The amplitudes of loudspeaker signals are a weighted combination of the zero order and first order harmonics of the elevation angle. It is proved that by choosing the weights of a combination properly, the current method is able to create an appropriate interaural time difference as well as its dynamic variation caused by head rotation and head tilting. Therefore, based on the classic Wallach’s hypothesis and its modern validations, the current method is able to create an appropriate dynamic cue for vertical localization at a low frequency. The results of psychoacoustic experiments indicate that the current method yields a reasonable localization performance and is superior to traditional pair-wise amplitude panning.

Binaural rendering of Ambisonic signals is of great interest in the fields of virtual reality, immersive media, and virtual acoustics. Typically, the spatial order of head-related impulse responses (HRIRs) is considerably higher than the order of the Ambisonic signals. The resulting order reduction of the HRIRs has a detrimental effect on the binaurally rendered signals, and perceptual evaluations indicate limited externalization, localization accuracy, and altered timbre. In this contribution, a binaural renderer, which is computed using a frequency-dependent time alignment of HRIRs followed by a minimization of the squared error subject to a diffuse-field covariance matrix constraint, is presented. The frequency-dependent time alignment retains the interaural time difference (at low frequencies) and results in a HRIR set with lower spatial complexity, while the constrained optimization controls the diffuse-field behavior. Technical evaluations in terms of sound coloration, interaural level differences, diffuse-field response, and interaural coherence, as well as findings from formal listening experiments show a significant improvement of the proposed method compared to state-of-the-art methods.

Numerical simulations offer a feasible alternative to the direct acoustic measurement of individual head-related transfer functions (HRTFs). For the acquisition of high quality 3D surface scans, as required for these simulations, several approaches exist. In this paper, we systematically analyze the variations between different approaches and evaluate the influence of the accuracy of 3D scans on the resulting simulated HRTFs. To assess this effect, HRTFs were numerically simulated based on 3D scans of the head and pinna of the FABIAN dummy head generated with 6 different methods. These HRTFs were analyzed in terms of interaural time difference, interaural level difference, energetic error in auditory filters and by their modeled localization performance. From the results, it is found that a geometric precision of about 1 mm is needed to maintain accurate localization cues, while a precision of about 4 mm is sufficient to maintain the overall spectral shape.

This work presents a novel technique that performs both orientation and distance localization of a sound source in a three-dimensional (3D) space using only the interaural time difference (ITD) cue, generated by a newly-developed self-rotational bi-microphone robotic platform. The system dynamics is established in the spherical coordinate frame using a state-space model. The observability analysis of the state-space model shows that the system is unobservable when the sound source is placed with elevation angles of $90$ and $0$ degree. The proposed method utilizes the difference between the azimuth estimates resulting from respectively the 3D and the two-dimensional models to check the zero-degree-elevation condition and further estimates the elevation angle using a polynomial curve fitting approach. Also, the proposed method is capable of detecting a $90$-degree elevation by extracting the zero-ITD signal 'buried' in noise. Additionally, a distance localization is performed by first rotating the microphone array to face toward the sound source and then shifting the microphone perpendicular to the source-robot vector by a predefined distance of a fixed number of steps. The integrated rotational and translational motions of the microphone array provide a complete orientation and distance localization using only the ITD cue. A novel robotic platform using a self-rotational bi-microphone array was also developed for unmanned ground robots performing sound source localization. The proposed technique was first tested in simulation and was then verified on the newly-developed robotic platform. Experimental data collected by the microphones installed on a KEMAR dummy head were also used to test the proposed technique. All results show the effectiveness of the proposed technique., Comment: The paper is under revision for 'Journal of Intelligent & Robotic Systems'

The question of how frequency is coded in the peripheral auditory system remains unresolved. Previous research has suggested that slow rates of frequency modulation (FM) of a low carrier frequency may be coded via phase-locked temporal information in the auditory nerve, whereas FM at higher rates and/or high carrier frequencies may be coded via a rate-place (tonotopic) code. This hypothesis was tested in a cohort of 100 young normal-hearing listeners by comparing individual sensitivity to slow-rate (1-Hz) and fast-rate (20-Hz) FM at a carrier frequency of 500 Hz with independent measures of phase-locking (using dynamic interaural time difference, ITD, discrimination), level coding (using amplitude modulation, AM, detection), and frequency selectivity (using forward-masking patterns). All FM and AM thresholds were highly correlated with each other. However, no evidence was obtained for stronger correlations between measures thought to reflect phase-locking (e.g., slow-rate FM and ITD sensitivity), or between measures thought to reflect tonotopic coding (fast-rate FM and forward-masking patterns). The results suggest that either psychoacoustic performance in young normal-hearing listeners is not limited by peripheral coding, or that similar peripheral mechanisms limit both high- and low-rate FM coding.

SUMMARY Hearing information is very important when visual information is limited. Sound source localization has been noted as particularly important in hearing information processing. Barn owls have excellent auditory processing. We propose a hardware model based on the auditory sense mechanism of barn owls. In this paper, we consider a model of the external nucleus of the inferior colliculus (ICx), which locates the source of a sound by the interaural time difference (ITD) for localization in the horizontal direction, and the interaural level difference (ILD) for localization in the vertical direction. The results show that the detection position of an ITD model and the detection position of an ILD model can converge. In addition, the output position of the ICx model changes with the position of the sound source.