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Streptococcus pneumoniae is a major human pathogen that can cause severe invasive diseases such as pneumonia, septicaemia and meningitis. Young children are at a particularly high risk, with an estimated 3–4 million cases of severe disease and between 300 000 and 500 000 deaths attributable to pneumococcal disease each year. The haemolytic toxin pneumolysin (Ply) is a primary virulence factor for this bacterium, yet despite its key role in pathogenesis, immune evasion and transmission, the regulation of Ply production is not well defined. Using a genome-wide association approach, we identified a large number of potential affectors of Ply activity, including a gene acquired horizontally on the antibiotic resistance-conferring Integrative and Conjugative Element (ICE) ICESp23FST81. This gene encodes a novel modular protein, ZomB, which has an N-terminal UvrD-like helicase domain followed by two Cas4-like domains with potent ATP-dependent nuclease activity. We found the regulatory effect of ZomB to be specific for the ply operon, potentially mediated by its high affinity for the BOX repeats encoded therein. Using a murine model of pneumococcal colonization, we further demonstrate that a ZomB mutant strain colonizes both the upper respiratory tract and lungs at higher levels when compared to the wild-type strain. While the antibiotic resistance-conferring aspects of ICESp23FST81 are often credited with contributing to the success of the S. pneumoniae lineages that acquire it, its ability to control the expression of a major virulence factor implicated in bacterial transmission is also likely to have played an important role.

Humans have evolved the unique capacity to efficiently communicate using the spoken word. Hearing plays a key role as a receiver in this process and dysfunction leads to difficulties in listening and communication. It is widely accepted that effective communication is not adequately captured with current behavioral speech tests that principally focus on passive sound detection and speech recognition with idealized stimuli. To address the question of what it will take to obtain more ecologically valid outcomes from behavioral speech tests, recent approaches, and test paradigms devised to address some of the acknowledged shortcomings of current speech tests were reviewed. Additionally, some recent work which has focused on understanding brain function in social and dynamic interaction scenarios, so-called second person neuroscience, was reviewed. These reviews revealed that, while recent efforts in bridging the gap between behavioral speech tests and everyday communication situations represent important steps in the right direction, they are unlikely to provide a complete account of everyday communication situations. Further, brain imaging studies, together with our growing understanding of "mirror" neurons and the development of theories around embodied cognition, have demonstrated that the brain networks recruited during emotionally engaged interaction between interlocutors are far more complex when compared to that of a passive listener. Speech and nonspeech (e.g., gaze direction, body posture, etc.) interactions between the interlocutors give rise to the perception of effective interaction (sense of "agency") and activate neural networks important in decision-making and subsequent communication interaction. Successful conversational interaction represents the negotiation of a dynamic context and the emergence of a state of shared understanding between participants. In conclusion, to achieve highly ecologically valid outcomes related to communication, future testing will most likely require an interactive or conversational paradigm to elicit the brain states that are present in everyday social interactions.

This manuscript describes a range of technical deliberations undertaken by the authors during their work as members of the Australian Government’s Independent Scientific Committee on Wind Turbines. Central to these deliberations was the requirement upon the committee to improve understanding and monitoring of the potential impacts of sound from wind turbines (including low frequency and infrasound) on health and the environment. The paper examines existing wind turbine sound limits, possible perceptual and physiological effects of wind turbine noise, aspects of the effects of wind turbine sound on sleep health and quality of life, low-frequency noise limits, the concept of annoyance including alternative causes of it and the potential for it to be affected by low-frequency noise, the influence of amplitude modulation and tonality, sound measurement and analysis and management strategies. In so doing it provides an objective basis for harmonisation across Australia of provisions for siting and monitoring of wind turbines, which currently vary from state to state, contributing to contention and potential inequities between Australians, depending on their place of residence.

Funding: William Demant Foundation

The outer-ear's location-dependent pattern of spectral filtering generates cues used to determine a sound source's elevation as well as front-back location. The authors aim to identify these features using a reverse correlation analysis (RCA), combining free-field localization behaviour with the associated head-related transfer functions' (HRTFs) magnitude spectrum from a sample of 73 participants. Localization responses were collected before and immediately after introducing a pair of outer-ear inserts which modified the listener's HRTFs to varying extent. The RCA identified several different features responsible for eliciting localization responses. The efficacy of these was examined using two models of monaural localization. In general, the predicted performance was closely aligned with the free-field localization error for the bare-ear condition; however, both models tended to grossly over-estimate the localization error based on HRTFs modified by the outer-ear inserts. The RCA's feature selection notably had the effect of better aligning the predicted performance of both models to the actual localization performance. This suggests that the RCA revealed sufficient detail for both models to correctly predict localization performance and also limited the influence of filtered-out elements in the distorted HRTFs that contributed to the degraded accuracy of both models.

Ecological validity is a relatively new concept in hearing science. It has been cited as relevant with increasing frequency in publications over the past 20 years, but without any formal conceptual basis or clear motive. The sixth Eriksholm Workshop was convened to develop a deeper understanding of the concept for the purpose of applying it in hearing research in a consistent and productive manner. Inspired by relevant debate within the field of psychology, and taking into account the World Health Organization's International Classification of Functioning, Disability, and Health framework, the attendees at the workshop reached a consensus on the following definition: "In hearing science, ecological validity refers to the degree to which research findings reflect real-life hearing-related function, activity, or participation." Four broad purposes for striving for greater ecological validity in hearing research were determined: A (Understanding) better understanding the role of hearing in everyday life; B (Development) supporting the development of improved procedures and interventions; C (Assessment) facilitating improved methods for assessing and predicting ability to accomplish real-world tasks; and D (Integration and Individualization) enabling more integrated and individualized care. Discussions considered the effects of variables and phenomena commonly present in hearing-related research on the level of ecological validity of outcomes, supported by examples from a few selected outcome domains and for different types of studies. Illustrated with examples, potential strategies were offered for promoting a high level of ecological validity in a study and for how to evaluate the level of ecological validity of a study. Areas in particular that could benefit from more research to advance ecological validity in hearing science include: (1) understanding the processes of hearing and communication in everyday listening situations, and specifically the factors that make listening difficult in everyday situations; (2) developing new test paradigms that include more than one person (e.g., to encompass the interactive nature of everyday communication) and that are integrative of other factors that interact with hearing in real-life function; (3) integrating new and emerging technologies (e.g., virtual reality) with established test methods; and (4) identifying the key variables and phenomena affecting the level of ecological validity to develop verifiable ways to increase ecological validity and derive a set of benchmarks to strive for.

In order to perceive meaningful speech, the auditory system must recognize different phonemes amidst a noisy and variable acoustic signal. To better understand the processing mechanisms underlying this ability, evoked cortical responses to different spoken consonants were measured with electroencephalography (EEG). Using multivariate pattern analysis (MVPA), binary classifiers attempted to discriminate between the EEG activity evoked by two given consonants at each peri-stimulus time sample, providing a dynamic measure of their cortical dissimilarity. To examine the relationship between representations at the auditory periphery and cortex, MVPA was also applied to modelled auditory-nerve (AN) responses of consonants, and time-evolving AN-based and EEG-based dissimilarities were compared with one another. Cortical dissimilarities between consonants were commensurate with their articulatory distinctions, particularly their manner of articulation, and to a lesser extent, their voicing. Furthermore, cortical distinctions between consonants in two periods of activity, centered at 130 and 400 ms after onset, aligned with their peripheral dissimilarities in distinct onset and post-onset periods, respectively. In relating speech representations across articulatory, peripheral, and cortical domains, the understanding of crucial transformations in the auditory pathway underlying the ability to perceive speech is advanced.

This study examined the effect of a change in target voice on word recall during a multi-talker conversation. Two experiments were conducted using matrix sentences to assess the cost of a single endogenous switch in non-spatial attention. Performance in a yes-no recognition task was significantly worse when a target voice changed compared to when it remained the same after a turn-taking gap. We observed a decrease in target hit rate and sensitivity, and an increase in masker confusion errors following a change in voice. These results highlight the cognitive demands of not only engaging attention on a new talker, but also of disengaging attention from a previous target voice. This shows that exposure to a voice can have a biasing effect on attention that persists well after a turn-taking gap. A second experiment showed that there was no change in switching performance using different talker combinations. This demonstrates that switching costs were consistent and did not depend on the degree of acoustic differences in target voice characteristics.

To develop, in Australian English, the first mixed-gender, multi-talker matrix sentence test.Speech material consisted of a 50-word base matrix whose elements can be combined to form sentences of identical syntax but unpredictable content. Ten voices (five female and five male) were recorded for editing and preliminary level equalization. Elements were presented as single-talker sentences-in-noise during two perceptual tests: an optimization phase that provided the basis for further level correction, and an evaluation phase that perceptually validated those changes.Ten listeners participated in the optimization phase; these and an additional 32 naïve listeners completed the evaluation test. All were fluent in English and all but one had lived in Australia for2 years.Optimization reduced the standard deviation (SD) and speech reception threshold (SRT) range across all speech material (grand mean SRT = -10.6 dB signal-to-noise ratio, median = -10.8, SD =1.4, range =13.7, slope =19.3%/dB), yielding data consistent with cross-validated matrix tests in other languages. Intelligibility differences between experienced and naïve listeners were minimal.The Australian matrix corpus provides a robust set of test materials suitable for both clinical assessment and research into the dynamics of active listening in multi-talker environments.

The location of a sound is derived computationally from acoustical cues rather than being inherent in the topography of the input signal, as in vision. Since Lord Rayleigh, the descriptions of that representation have swung between “labeled line” and “opponent process” models. Employing a simple variant of a two-point separation judgment using concurrent speech sounds, we found that spatial discrimination thresholds changed nonmonotonically as a function of the overall separation. Rather than increasing with separation, spatial discrimination thresholds first declined as two-point separation increased before reaching a turning point and increasing thereafter with further separation. This “dipper” function, with a minimum at 6 ° of separation, was seen for regions around the midline as well as for more lateral regions (30 and 45 °). The discrimination thresholds for the binaural localization cues were linear over the same range, so these cannot explain the shape of these functions. These data and a simple computational model indicate that the perception of auditory space involves a local code or multichannel mapping emerging subsequent to the binaural cue coding.

The article A Review of the Potential Impacts of Wind Turbine Noise in the Australian Context, written by John Laurence Davy, Kym Burgemeister, David Hillman & Simon Carlile, was originally published electronically on the publisher’s internet portal on 27 June 2020 without open access.

In music, the perception of pitch is governed largely by its tonal function given the preceding harmonic structure of the music. While behavioral research has advanced our understanding of the perceptual representation of musical pitch, relatively little is known about its representational structure in the brain. Using Magnetoencephalography (MEG), we recorded evoked neural responses to different tones presented within a tonal context. Multivariate Pattern Analysis (MVPA) was applied to “decode” the stimulus that listeners heard based on the underlying neural activity. We then characterized the structure of the brain’s representation using decoding accuracy as a proxy for representational distance, and compared this structure to several well established perceptual and acoustic models. The observed neural representation was best accounted for by a model based on the Standard Tonal Hierarchy, whereby differences in the neural encoding of musical pitches correspond to their differences in perceived stability. By confirming that perceptual differences honor those in the underlying neuronal population coding, our results provide a crucial link in understanding the cognitive foundations of musical pitch across psychological and neural domains.

PurposeThe aim of this study was to examine attention, memory, and auditory processing in children with reported listening difficulty in noise (LDN) despite having clinically normal hearing.MethodTwenty-one children with LDN and 15 children with no listening concerns (controls) participated. The clinically normed auditory processing tests included the Frequency/Pitch Pattern Test (FPT; Musiek, 2002), the Dichotic Digits Test (Musiek, 1983), the Listening in Spatialized Noise—Sentences (LiSN–S) test (Dillon, Cameron, Glyde, Wilson, & Tomlin, 2012), gap detection in noise (Baker, Jayewardene, Sayle, & Saeed, 2008), and masking level difference (MLD; Wilson, Moncrieff, Townsend, & Pillion, 2003). Also included were research-based psychoacoustic tasks, such as auditory stream segregation, localization, sinusoidal amplitude modulation (SAM), and fine structure perception. All were also evaluated on attention and memory test batteries.ResultsThe LDN group was significantly slower switching their auditory attention and had poorer inhibitory control. Additionally, the group mean results showed significantly poorer performance on FPT, MLD, 4-Hz SAM, and memory tests. Close inspection of the individual data revealed that only 5 participants (out of 21) in the LDN group showed significantly poor performance on FPT compared with clinical norms. Further testing revealed the frequency discrimination of these 5 children to be significantly impaired.ConclusionThus, the LDN group showed deficits in attention switching and inhibitory control, whereas only a subset of these participants demonstrated an additional frequency resolution deficit.

The capacity of healthy adult listeners to accommodate to altered spectral cues to the source locations of broadband sounds has now been well documented. In recent years we have demonstrated that the degree and speed of accommodation are improved by using an integrated sensory-motor training protocol under anechoic conditions. Here we demonstrate that the learning which underpins the localization performance gains during the accommodation process using anechoic broadband training stimuli generalize to environmentally relevant scenarios. As previously, alterations to monaural spectral cues were produced by fitting participants with custom-made outer ear molds, worn during waking hours. Following acute degradations in localization performance, participants then underwent daily sensory-motor training to improve localization accuracy using broadband noise stimuli over ten days. Participants not only demonstrated post-training improvements in localization accuracy for broadband noises presented in the same set of positions used during training, but also for stimuli presented in untrained locations, for monosyllabic speech sounds, and for stimuli presented in reverberant conditions. These findings shed further light on the neuroplastic capacity of healthy listeners, and represent the next step in the development of training programs for users of assistive listening devices which degrade localization acuity by distorting or bypassing monaural cues.

In recent years, a great deal of research within the field of sound localization has been aimed at finding the acoustic cues that human listeners use to localize sounds and understanding the mechanisms by which they process these cues. In this paper, we propose a complementary approach by constructing an ideal-observer model, by which we mean a model that performs optimal information processing within a Bayesian context. The model considers all available spatial information contained within the acoustic signals encoded by each ear. Parameters for the optimal Bayesian model are determined based on psychoacoustic discrimination experiments on interaural time difference and sound intensity. Without regard as to how the human auditory system actually processes information, we examine the best possible localization performance that could be achieved based only on analysis of the input information, given the constraints of the normal auditory system. We show that the model performance is generally in good agreement with the actual human localization performance, as assessed in a meta-analysis of many localization experiments (Best et al. in Principles and applications of spatial hearing, pp 1423. World Scientific Publishing, Singapore, 2011). We believe this approach can shed new light on the optimality (or otherwise) of human sound localization, especially with regard to the level of uncertainty in the input information. Moreover, the proposed model allows one to study the relative importance of various (combinations of) acoustic cues for spatial localization and enables a prediction of which cues are most informative and therefore likely to be used by humans in various circumstances.

Previous research has demonstrated that, over a period of weeks, the auditory system accommodates to changes in the monaural spectral cues for sound locations within the frontal region of space. We were interested to determine if similar accommodation could occur for locations in the posterior regions of space, i.e. in the absence of contemporaneous visual information that indicates any mismatch between the perceived and actual location of a sound source. To distort the normal spectral cues to sound location, eight listeners wore small moulds in each ear. HRTF recordings confirmed that while the moulds substantially altered the monaural spectral cues, sufficient residual cues were retained to provide a basis for relearning. Compared to control measures, sound localization performance initially decreased significantly, with a sevenfold increase in front–back confusions and elevation errors more than doubled. Subjects wore the moulds continuously for a period of up to 60 days (median 38 days), over which time performance improved but remained significantly poorer than control levels. Sound localization performance for frontal locations (audio-visual field) was compared with that for posterior space (audio-only field), and there was no significant difference between regions in either the extent or rate of accommodation. This suggests a common mechanism for both regions of space that does not rely on contemporaneous visual information as a teacher signal for recalibration of the auditory system to modified spectral cues.

A natural auditory scene often contains sound moving at varying velocities. Using a velocity contrast paradigm, we compared sensitivity to velocity changes between continuous and discontinuous trajectories. Subjects compared the velocities of two stimulus intervals that moved along a single trajectory, with and without a 1 second inter stimulus interval (ISI). We found thresholds were threefold larger for velocity increases in the instantaneous velocity change condition, as compared to instantaneous velocity decreases or thresholds for the delayed velocity transition condition. This result cannot be explained by the current static “snapshot” model of auditory motion perception and suggest a continuous process where the percept of velocity is influenced by previous history of stimulation.

The growing availability of efficient and relatively inexpensive virtual auditory display technology has provided new research platforms to explore the perception of auditory motion. At the same time, deployment of these technologies in command and control as well as in entertainment roles is generating an increasing need to better understand the complex processes underlying auditory motion perception. This is a particularly challenging processing feat because it involves the rapid deconvolution of the relative change in the locations of sound sources produced by rotational and translations of the head in space (self-motion) to enable the perception of actual source motion. The fact that we perceive our auditory world to be stable despite almost continual movement of the head demonstrates the efficiency and effectiveness of this process. This review examines the acoustical basis of auditory motion perception and a wide range of psychophysical, electrophysiological, and cortical imaging studies that have probed the limits and possible mechanisms underlying this perception.

The ability to actively follow a moving auditory target with our heads remains unexplored even though it is a common behavioral response. Previous studies of auditory motion perception have focused on the condition where the subjects are passive. The current study examined head tracking behavior to a moving auditory target along a horizontal 100° arc in the frontal hemisphere, with velocities ranging from 20°/s to 110°/s. By integrating high fidelity virtual auditory space with a high-speed visual presentation we compared tracking responses of auditory targets against visual-only and audio-visual “bisensory” stimuli. Three metrics were measured – onset, RMS and gain error. The results showed that tracking accuracy (RMS error) varied linearly with target velocity, with a significantly higher rate in audition. Also, when the target moved faster than 80°/s, onset and RMS error were significantly worst in audition the other modalities while responses in the visual and bisensory conditions were statistically identical for all metrics measured. Lastly, audio-visual facilitation was not observed when tracking bisensory targets.

This review considers the nature of the sound generated by wind turbines focusing on the low-frequency sound (LF) and infrasound (IS) to understand the usefulness of the sound measures where people work and sleep. A second focus concerns the evidence for mechanisms of physiological transduction of LF/IS or the evidence for somatic effects of LF/IS. While the current evidence does not conclusively demonstrate transduction, it does present a strong prima facia case. There are substantial outstanding questions relating to the measurement and propagation of LF and IS and its encoding by the central nervous system relevant to possible perceptual and physiological effects. A range of possible research areas are identified.

Speech reception thresholds (SRTs) were measured at a central focus of attention and at 20 degrees, 40 degrees, and 60 degrees locations distant in azimuth. Measurements were taken with one target collocated with two maskers, or with maskers flanking the target by +/-20 degrees. For 80% of trials, the target was played from the attended location ("expected"), and 20% came from another ("unexpected") location. For collocated stimuli, SRTs worsened with increasing distance from the expected location by 2.1 dB over the 60 degrees azimuth and by 5.1 dB for spatially separated target and maskers. In spatially separated conditions, a 2.9-dB change was still found when gaze was away from the attended location. Spatial attention appears to increase speech intelligibility against interferers, with gain decreasing with distance from the focus of attention. Spatial release from masking (RFM) was only found for the attended location. Further experiments suggest that target location uncertainty prevented RFM at unattended locations.

Auditory localisation was examined using brief broadband sounds presented during rapid head turns to visual targets in the peripheral field. Presenting sounds during a rapid head movement will "smear" the acoustic cues to the sound's location. During the early stages of a head turn, sound localisation accuracy was comparable to a no-turn control condition. However, significant localisation errors occurred when the probe sound was presented during the later part of a head turn. After correcting for head position, the estimate of lateral angle (horizontal position) in the front hemisphere was generally accurate. However, lateral angle estimates for positions in the rear hemisphere exhibited systematic errors that were especially large around the midline. Polar angle (elevation) perception remained robust, being comparable to no-turn controls whether tested early or late in the head turn. The results are interpreted in terms of a 'multiple look' strategy for calculating sound location, and the allocation of attention to the hemisphere containing the head-turn target.

To examine whether auditory streaming contributes to unmasking, intelligibility of target sentences against two competing talkers was measured using the coordinate response measure (CRM) [Bolia et al., J. Acoust. Soc. Am. 107, 1065-1066 (2007)] corpus. In the control condition, the speech reception threshold (50% correct) was measured when the target and two maskers were collocated straight ahead. Separating maskers from the target by +/-30 degrees resulted in spatial release from masking of 12 dB. CRM sentences involve an identifier in the first part and two target words in the second part. In experimental conditions, masking talkers started spatially separated at +/-30 degrees but became collocated with the target before the scoring words. In one experiment, one target and two different maskers were randomly selected from a mixed-sex corpus. Significant unmasking of 4 dB remained despite the absence of persistent location cues. When same-sex talkers were used as maskers and target, unmasking was reduced. These data suggest that initial separation may permit confident identification and streaming of the target and masker speech where significant differences between target and masker voice characteristics exist, but where target and masker characteristics are similar, listeners must rely more heavily on continuing spatial cues.

Following a multi-talker conversation relies on the ability to rapidly and efficiently shift the focus of spatial attention from one talker to another. The current study investigated the listening costs associated with shifts in spatial attention during conversational turn-taking in 16 normally-hearing listeners using a novel sentence recall task. Three pairs of syntactically fixed but semantically unpredictable matrix sentences, recorded from a single male talker, were presented concurrently through an array of three loudspeakers (directly ahead and +/-30° azimuth). Subjects attended to one spatial location, cued by a tone, and followed the target conversation from one sentence to the next using the call-sign at the beginning of each sentence. Subjects were required to report the last three words of each sentence (speech recall task) or answer multiple choice questions related to the target material (speech comprehension task). The reading span test, attention network test, and trail making test were also administered to assess working memory, attentional control, and executive function. There was a 10.7 ± 1.3% decrease in word recall, a pronounced primacy effect, and a rise in masker confusion errors and word omissions when the target switched location between sentences. Switching costs were independent of the location, direction, and angular size of the spatial shift but did appear to be load dependent and only significant for complex questions requiring multiple cognitive operations. Reading span scores were positively correlated with total words recalled, and negatively correlated with switching costs and word omissions. Task switching speed (Trail-B time) was also significantly correlated with recall accuracy. Overall, this study highlights (i) the listening costs associated with shifts in spatial attention and (ii) the important role of working memory in maintaining goal relevant information and extracting meaning from dynamic multi-talker conversations.

To hear out a conversation against other talkers listeners overcome energetic and informational masking. Largely attributed to top-down processes, information masking has also been demonstrated using unintelligible speech and amplitude-modulated maskers suggesting bottom-up processes. We examined the role of speech-like amplitude modulations in information masking using a spatial masking release paradigm. Separating a target talker from two masker talkers produced a 20 dB improvement in speech reception threshold; 40% of which was attributed to a release from informational masking. When across frequency temporal modulations in the masker talkers are decorrelated the speech is unintelligible, although the within frequency modulation characteristics remains identical. Used as a masker as above, the information masking accounted for 37% of the spatial unmasking seen with this masker. This unintelligible and highly differentiable masker is unlikely to involve top-down processes. These data provides strong evidence of bottom-up masking involving speech-like, within-frequency modulations and that this, presumably low level process, can be modulated by selective spatial attention.

Because of the slow speed of sound relative to light, acoustic and visual signals from a distant event often will be received asynchronously. Here, using acoustic signals with a robust cue to sound source distance, we show that judgments of perceived temporal alignment with a visual marker depend on the depth simulated in the acoustic signal. For distant sounds, a large delay of sound relative to vision is required for the signals to be perceived as temporally aligned. For nearer sources, the time lag corresponding to audiovisual alignment is smaller and scales at rate approximating the speed of sound. Thus, when robust cues to auditory distance are present, the brain can synchronize disparate audiovisual signals to external events despite considerable differences in time of arrival at the perceiver. This ability is functionally important as it allows auditory and visual signals to be synchronized to the external event that caused them.

Virtual auditory space (VAS) stimuli based on outer ear transfer functions became increasingly important in spatial hearing research. However, few studies have investigated the match between responses of auditory neurons to VAS and free-field (FF) stimulation. This study validates acoustic spatial receptive fields (SRFs) of 183 individual midbrain units using both VAS and FF stimuli. The first-spike latency, which varied systematically across SRFs, was 14.9 +/- 8.3 (SD) ms in FF, and 15.1 +/- 8.3 ms in VAS. Spike-count-based SRFs measured 0-20 dB above the neural threshold covered on average 44.5 +/- 18.0% of the recorded sphere in FF and 45.5 +/- 18.7% in VAS. The average deviation of the centroid position of SRFs using FF and VAS stimuli was 7.4 degrees azimuth and 3.3 degrees elevation. The average spike rate remained unchanged. The SRF overlap recorded using FF and VAS stimuli (mean: 71.3 +/- 12.6%) or repeated FF stimuli (70.2 +/- 14.2%) was high and strongly correlated (r = 0.96; P0.05). The SRF match observed with FF and VAS stimuli was not significantly altered over a range of stimulus levels (paired t-test P = 0.51; n = 6). Randomized VAS barely affected SRF sizes, centroids, or maximum spike count but decreased the average minimum response to 59% compared with sequential stimulation (paired t-test; P = 0.05; n = 26). SRF recordings in VAS excluding the acoustic distortions of the recording equipment differed from those in VAS incorporating the equipment (paired t-test P = 0.01; n = 5). In conclusion, neurophysiological recordings demonstrate that individualized VAS stimuli provided a good simulation of a FF environment.

A human psychoacoustical experiment is described that investigates the role of the monaural and interaural spectral cues in human sound localization. In particular, it focuses on the relative contribution of the monaural versus the interaural spectral cues towards resolving directions within a cone of confusion (i.e., directions with similar interaural time and level difference cues) in the auditory localization process. Broadband stimuli were presented in virtual space from 76 roughly equidistant locations around the listener. In the experimental conditions, a "false" flat spectrum was presented at the left eardrum. The sound spectrum at the right eardrum was then adjusted so that either the true right monaural spectrum or the true interaural spectrum was preserved. In both cases, the overall interaural time difference and overall interaural level difference were maintained at their natural values. With these virtual sound stimuli, the sound localization performance of four human subjects was examined. The localization performance results indicate that neither the preserved interaural spectral difference cue nor the preserved right monaural spectral cue was sufficient to maintain accurate elevation judgments in the presence of a flat monaural spectrum at the left eardrum. An explanation for the localization results is given in terms of the relative spectral information available for resolving directions within a cone of confusion.

The effect of spatial separation on the ability of human listeners to resolve a pair of concurrent broadband sounds was examined. Stimuli were presented in a virtual auditory environment using individualized outer ear filter functions. Subjects were presented with two simultaneous noise bursts that were either spatially coincident or separated (horizontally or vertically), and responded as to whether they perceived one or two source locations. Testing was carried out at five reference locations on the audiovisual horizon (0 degrees, 22.5 degrees, 45 degrees, 67.5 degrees, and 90 degrees azimuth). Results from experiment 1 showed that at more lateral locations, a larger horizontal separation was required for the perception of two sounds. The reverse was true for vertical separation. Furthermore, it was observed that subjects were unable to separate stimulus pairs if they delivered the same interaural differences in time (ITD) and level (ILD). These findings suggested that the auditory system exploited differences in one or both of the binaural cues to resolve the sources, and could not use monaural spectral cues effectively for the task. In experiments 2 and 3, separation of concurrent noise sources was examined upon removal of low-frequency content (and ITDs), onset/offset ITDs, both of these in conjunction, and all ITD information. While onset and offset ITDs did not appear to play a major role, differences in ongoing ITDs were robust cues for separation under these conditions, including those in the envelopes of high-frequency channels.

Here we report the methods and output of a workshop examining possible futures of speech and hearing science out to 2030. Using a design thinking approach, a range of human-centered problems in communication were identified that could provide the motivation for a wide range of research. Nine main research programs were distilled and are summarized: (a) measuring brain and other physiological parameters, (b) auditory and multimodal displays of information, (c) auditory scene analysis, (d) enabling and understanding shared auditory virtual spaces, (e) holistic approaches to health management and hearing impairment, (f) universal access to evolving and individualized technologies, (g) biological intervention for hearing dysfunction, (h) understanding the psychosocial interactions with technology and other humans as mediated by technology, and (i) the impact of changing models of security and privacy. The design thinking approach attempted to link the judged level of importance of different research areas to the “end in mind” through empathy for the real-life problems embodied in the personas created during the workshop.

Changing the shape of the outer ear using small in-ear molds degrades sound localization performance consistent with the distortion of monaural spectral cues to location. It has been shown recently that adult listeners re-calibrate to these new spectral cues for locations both inside and outside the visual field. This raises the question as to the teacher signal for this remarkable functional plasticity. Furthermore, large individual differences in the extent and rate of accommodation suggests a number of factors may be driving this process. A training paradigm exploiting multi-modal and sensory-motor feedback during accommodation was examined to determine whether it might accelerate this process. So as to standardize the modification of the spectral cues, molds filling 40% of the volume of each outer ear were custom made for each subject. Daily training sessions for about an hour, involving repetitive auditory stimuli and exploratory behavior by the subject, significantly improved the extent of accommodation measured by both front-back confusions and polar angle localization errors, with some improvement in the rate of accommodation demonstrated by front-back confusion errors. This work has implications for both the process by which a coherent representation of auditory space is maintained and for accommodative training for hearing aid wearers.

This study compared the head-related transfer functions (HRTFs) recorded from the bare ear of a mannequin for 393 spatial locations and for five different hearing aid styles: Invisible-in-the-canal (IIC), completely-in-the-canal (CIC), in-the-canal (ITC), in-the-ear (ITE), and behind-the-ear (BTE). The spectral distortions of each style compared to the bare ear were described qualitatively in terms of the gain and frequency characteristics of the prominent spectral notch and two peaks in the HRTFs. Two quantitative measures of the differences between the HRTF sets and a measure of the dissimilarity of the HRTFs within each set were also computed. In general, the IIC style was most similar and the BTE most dissimilar to the bare ear recordings. The relative similarities among the CIC, ITC, and ITE styles depended on the metric employed. The within-style spectral dissimilarities were comparable for the bare ear, IIC, CIC, and ITC with increasing ambiguity for the ITE and BTE styles. When the analysis bandwidth was limited to 8 kHz, the HRTFs within each set became much more similar.