Auditory Spatial Cues Research Articles

Covert auditory spatial orienting: An evaluation of the spatial relevance hypothesis.

The spatial relevance hypothesis (J. J. McDonald & L. M. Ward, 1999) proposes that covert auditory spatial orienting can only be beneficial to auditory processing when task stimuli are encoded spatially. We present a series of experiments that evaluate 2 key aspects of the hypothesis: (a) that "reflexive activation of location-sensitive neurons is not sufficient to produce attentional facilitation" and (b) that "any task constraint that makes space important for the listener will produce auditory spatial cue effects" (p. 1236). Experiment 1 showed significant reflexive-orienting benefits on a nonspatial task, refuting the first claim. However, Experiments 2 to 4 reveal that informative spatial cues can improve performance on a nonspatial task, consistent with the second claim. Auditory spatial-cue benefits found with nonspatial tasks appear smaller and less reliable than those found in visual spatial-orienting studies, possibly due to differences in the coding of spatial information in vision and audition. The final experiments consider the mechanisms by which auditory spatial orienting might facilitate auditory processing and provide tentative evidence that attention enhances processing at one ear rather than influencing neurons tuned to the attended location.

Blind and naked, but oh so cool: The subterranean world of the naked mole‐rat

Are big ears, tails, and eyes simply anatomical "junk" to subterranean mammals? These animals show remarkable convergent evolution for reducing external ears, tails, and eyes. The naked mole‐rat (NMR, Heterocephalus glaber) displays these features, as well as unusual characteristics even among subterraneans (cold‐blooded and completely furless). Whereas visual and auditory spatial cues are of diminished importance, NMRs are specialized for alternative modalities (primarily via mechanoceptors). We are studying yet other unusual characteristics, which include two structures that may be heading for the anatomical junk pile. First, the NMR is the only mammal with a vomeronasal organ (VNO) that shows no post‐natal growth and sexual suppression is not mediated by urinary signals as in other rodents. Second, the nerve network for processing pain from chemicals (acid and capsaicin) is reduced and lacks neuropeptides that usually signal pain. NMRs are the only mammals that feel no pain from these substances. These features may be a result of this species' unusual combination of lifestyle traits (subterranean + hundreds of individuals + extremely social), resulting in CO2 levels high enough to cause acidosis and chemical pain. Coincidentally, the neuropeptides that are lacking from the pain system also mediate the VNO's vascular pump. NMRs provide unique insights into sensory specialization and evolutionary loss.

Reference Frame Congruency in Search-and-Rescue Tasks

Our aim was to investigate how the congruency between visual displays and auditory cues affects performance on various spatial tasks. Previous studies have demonstrated that spatial auditory cues, when combined with visual displays, can enhance performance and decrease workload. However, this facilitation was achieved only when auditory cues shared a common reference frame (RF) with the visual display. In complex and dynamic environments, such as airborne search and rescue (SAR), it is often difficult to ensure such congruency. In a simulated SAR operation, participants performed three spatial tasks: target search, target localization, and target recall. The interface consisted of the camera view of the terrain from the aircraft-mounted sensor, a map of the area flown over, a joystick that controlled the sensor, and a mouse. Auditory cues were used to indicate target location. While flying in the scenario, participants searched for targets, identified their locations in one of two coordinate systems, and memorized their location relative to the terrain layout. Congruent cues produced the fastest and most accurate performance. Performance advantages were observed even with incongruent cues relative to neutral cues, and egocentric cues were more effective than exocentric cues. Although the congruent cues are most effective, in cases in which the same cue is used across spatial tasks, egocentric cues are a better choice than exocentric cues. Egocentric auditory cues should be used in display design for tasks that involve RF transformations, such as SAR, air traffic control, and unmanned aerial vehicle operations.

Sensitivity to interaural level differences in high‐rate high‐frequency click trains: A functional magnetic resonance imaging assessment.

While the auditory cortex (AC) is known to be necessary for accurate sound localization, the nature of spatial representation in AC remains poorly understood. Past animal studies have quantified sensitivity to auditory spatial cues [e.g., interaural level difference (ILD)] across subregions of AC. In this study, functional magnetic resonance imaging (fMRI) was used to assess ILD sensitivity across the surface of human AC. Normal‐hearing listeners were presented with narrowband Gabor click trains (4000 Hz center frequency, 3 ms interclick interval) that varied parametrically in ILD over a range of +/− 30 dB. Simultaneously, whole‐head fMRI images were acquired using a sparse imaging paradigm at 3 Tesla (32‐slice EPI, 3.0×3.0×4.5 mm resolution, TR=12 s). During imaging, listeners detected rare target changes in ICI. Hemodynamic responses of compact AC subregions in individual subjects were assessed quantitatively using statistical pattern recognition with two goals: (1) to identify contiguous AC regions that share common patterns of sensitivity to ILD, and (2) to quantify, in information‐theoretic terms, the ability of those responses to differentiate stimuli differing in ILD.

Bimodal task-facilitation in a virtual traffic scenario through spatialized sound rendering

Audio rendering is generally used to increase the realism of virtual environments (VE). In addition, audio rendering may also improve the performance in specific tasks carried out in interactive applications such as games or simulators. In this article we investigate the effect of the quality of sound rendering on task performance in a task which is inherently vision-dominated. The task is a virtual traffic gap-crossing scenario with two elements: first, to discriminate crossable and uncrossable gaps in oncoming traffic, and second, to find the right timing to start crossing the street without an accident. A study was carried out with 48 participants in an immersive virtual environment setup with a large screen and headphones. Participants were grouped into three different scenarios. In the first one, spatialized audio rendering with head-related transfer function (HRTF) filtering was used. The second group was tested with conventional stereo rendering, and the remaining group ran the experiment in a mute condition. Our results give a clear evidence that spatialized audio improves task performance compared to the unimodal mute condition. Since all task-relevant information was in the participants' field-of-view, we conclude that an enhancement of task performance results from a bimodal advantage due to the integration of visual and auditory spatial cues.

Visual influences on auditory spatial learning

The visual and auditory systems frequently work together to facilitate the identification and localization of objects and events in the external world. Experience plays a critical role in establishing and maintaining congruent visual–auditory associations, so that the different sensory cues associated with targets that can be both seen and heard are synthesized appropriately. For stimulus location, visual information is normally more accurate and reliable and provides a reference for calibrating the perception of auditory space. During development, vision plays a key role in aligning neural representations of space in the brain, as revealed by the dramatic changes produced in auditory responses when visual inputs are altered, and is used throughout life to resolve short-term spatial conflicts between these modalities. However, accurate, and even supra-normal, auditory localization abilities can be achieved in the absence of vision, and the capacity of the mature brain to relearn to localize sound in the presence of substantially altered auditory spatial cues does not require visuomotor feedback. Thus, while vision is normally used to coordinate information across the senses, the neural circuits responsible for spatial hearing can be recalibrated in a vision-independent fashion. Nevertheless, early multisensory experience appears to be crucial for the emergence of an ability to match signals from different sensory modalities and therefore for the outcome of audiovisual-based rehabilitation of deaf patients in whom hearing has been restored by cochlear implantation.

Spatiotemporal interactions between audition and vision

It is well known that spatial auditory cues can affect performance on spatial visual tasks. One example is crossmodal cueing: response times for a visual spatial discrimination task are shortened when the location of the visual stimuli is cued auditorily, and prolonged when an invalid location is cued. Another example is auditory support of visual search: we normally find lower search times for visual items when the location of the target item is indicated by an auditory cue. In our research we have explored two questions: one related to crossmodal cueing, and the other to audiovisual search. In our crossmodal cueing paradigm we have looked at the interaction between (exogenous) cueing and endogenous information given before each trial. In this way we wanted to determine whether auditory cues are able to capture visual attention even when this attention has already been focused endogenously. In our audiovisual search paradigm we have studied whether nonspatial auditory cues, presented simultaneously with the visual target item, are able to improve visual search. Because of the temporal synchrony, the auditory stimuli do not act as actual cues but they are probably fused with the visual stimuli into an integrated percept.

The effects of fluctuating interaural cues on the segregation of speech in rooms: Revisited

Spatial separation is known to improve the segregation of talkers in anechoic environments, but spatial auditory cues can be severely degraded in reverberant rooms. One might expect the random disruptions in the interaural time and level differences (ILDs and ITDs) that occur in reverberant environments to eliminate many of the intelligibility benefits that normally occur for spatially separated speech. However, the precedence effect often leads to a robust perception of spatial location even in extremely echoic environments. This can result in an apparent separation between talkers that may facilitate selective attention to the location of the target speech even in a highly reverberant room. Also, random fluctuations in ITD and ILD may lead to differences in the apparent source widths of the target and masking sounds, which might serve as a segregation cue. In this talk, we examine the effects fluctuating interaural difference cues have on the segregation of target speech from competing speech or noise. These results, originally scheduled for presentation at the 152nd meeting, suggest that differences in apparent source width can be used to segregate competing speech signals even when the target and masking signals appear to originate from the same direction relative to the listener.

Attention to human speakers in a virtual auditory environment: Brain potential evidence

Listening to a speech message requires the accurate selection of the relevant auditory input especially when distracting background noise or other speech messages are present. To investigate such auditory selection processes we presented three different speech messages simultaneously spoken by different actors at separate spatial locations (− 70, 0, 70/ azimuth). Stimuli were recorded using an artificial head with microphones embedded in the “auditory canals” to capture the interaural time and level differences as well as some of the filter properties of the outer ear structures as auditory spatial cues, thus creating a realistic virtual auditory space. In a given experimental run young healthy participants listened via headphones and either attended to the rightmost or the leftmost message in order to comprehend the story. Superimposed on the speech messages task irrelevant probe stimuli (syllables sharing spatial and spectral characteristics, 4 probes/s) were presented that were used for the generation of event-related brain potentials computed from 29 channels of EEG. ERPs to probe stimuli were characterized by a negativity starting at 250 ms with a contralateral frontal maximum for the probes sharing spatial/spectral features of the attended story relative to those for the unattended message. The relatively late onset of this attention effect was interpreted to reflect the task demands in this complex auditory environment. This study demonstrates the feasibility to use virtual auditory environments in conjunction with the probe technique to study auditory selection under realistic conditions.

Spatial generalization in short-term perceptual adaptation to novel auditory spaces

Previous work shows that humans can rapidly adapt to novel mappings between auditory spatial cues and exocentric location and localize accurately with the novel mapping. Here, experiments using (1) a rotation and (2) a linear magnification of auditory space examined generalization of spatial adaptation to untrained or neglected regions of space. Individual head-related transfer functions (HRTFs) were used to simulate different source locations using headphones. Each experimental session was broken into three blocks: initial normal cues (measuring baseline performance), altered cues (showing adaptation), and final normal cues (measuring an adaptation aftereffect). In the altered cues trials, a source at X degrees was simulated using HRTFs that normally correspond to a source at (1) X+30 deg (rotation) or (2) 2X deg (linear magnification). After obtaining subjects’ localization responses to the sound stimulus, feedback was given using a light-emitting diode located at the correct position (X deg). Results of these experiments show the extent to which training subjects to adjust their localization responses in one region of space affects how they localize sources in adjacent regions, and provide a measure of the spatial kernel that drives spatial auditory adaptation.

Congruency between Visual and Auditory Displays on Spatial Tasks Using Different Reference Frames

This study investigated the effectiveness of spatial auditory cues for tasks using different reference frames, and examined how congruency between auditory and visual displays affected performance. Performance with three types of auditory cues (egocentric, exocentric and non-spatial) was compared on three spatial tasks: target search, target localization and target recall. There was a clear effect of reference frame congruency between auditory and visual displays on target search and target localization tasks. Interestingly, even incongruent auditory cues improved performance relative to non-spatial control conditions. In addition, egocentric auditory cues facilitated performance more than exocentric cues on incongruent trials. The findings have important implications for display design in work environments that involve diverse spatial tasks and displays that use different reference frames.

Presentation modality influences behavioral measures of alerting, orienting, and executive control

The Attention Network Test (ANT) uses visual stimuli to separately assess the attentional skills of alerting (improved performance following a warning cue), spatial orienting (an additional benefit when the warning cue also cues target location), and executive control (impaired performance when a target stimulus contains conflicting information). This study contrasted performance on auditory and visual versions of the ANT to determine whether the measures it obtains are influenced by presentation modality. Forty healthy volunteers completed both auditory and visual tests. Reaction-time measures of executive control were of a similar magnitude and significantly correlated, suggesting that executive control might be a supramodal resource. Measures of alerting were also comparable across tasks. In contrast, spatial-orienting benefits were obtained only in the visual task. Auditory spatial cues did not improve response times to auditory targets presented at the cued location. The different spatial-orienting measures could reflect either separate orienting resources for each perceptual modality, or an interaction between a supramodal orienting resource and modality-specific perceptual processing.

Training-Induced Plasticity of Auditory Localization in Adult Mammals

Accurate auditory localization relies on neural computations based on spatial cues present in the sound waves at each ear. The values of these cues depend on the size, shape, and separation of the two ears and can therefore vary from one individual to another. As with other perceptual skills, the neural circuits involved in spatial hearing are shaped by experience during development and retain some capacity for plasticity in later life. However, the factors that enable and promote plasticity of auditory localization in the adult brain are unknown. Here we show that mature ferrets can rapidly relearn to localize sounds after having their spatial cues altered by reversibly occluding one ear, but only if they are trained to use these cues in a behaviorally relevant task, with greater and more rapid improvement occurring with more frequent training. We also found that auditory adaptation is possible in the absence of vision or error feedback. Finally, we show that this process involves a shift in sensitivity away from the abnormal auditory spatial cues to other cues that are less affected by the earplug. The mature auditory system is therefore capable of adapting to abnormal spatial information by reweighting different localization cues. These results suggest that training should facilitate acclimatization to hearing aids in the hearing impaired.

Body Orientation and the Perception of Spatial Auditory and Tactile Cues

This study investigated the effects of five body orientations (supine, kneeling, sitting, standing, and prone) on perception of spatial auditory and spatial tactile cues along eight equidistant points (45° separation) of the azimuth, using a within-participant design. Participants (N = 30) used a graphics tablet and stylus to indicate the perceived direction indicated by either vibrotactile stimuli applied to the abdomen, or spatial auditory stimuli presented via headphones. Response time data show responses to spatial tactile cues were significantly faster than spatial auditory cues at each body position and for each point along the azimuth, with no significant effects of body orientation. Absolute angle differences between presented and perceived cues were significantly smaller in the tactile condition for five of the eight stimulus positions, with no significant effects of body orientation. Results are discussed in terms of designing multi-sensory directional cues for reducing visual search space for dismounted soldiers

Processing of auditory spatial cues in human cortex: An fMRI study

The issue of where in the human cortex coding of sound location is represented still is a matter of debate. It is unclear whether there are cortical areas that are specifically activated depending on the location of sound. Are identical or distinct cortical areas in one hemisphere involved in processing of sounds from the left and right? Also, the possibility has not been investigated so far that distinct areas have a preference for processing of central and eccentric sound locations. The present study focussed on these issues by using functional magnetic resonance imaging (fMRI). Activations evoked by left, right and central sounds were analysed separately, and contrasts were computed between these conditions. We did not find areas, which were involved in the processing of exclusively left, right or central sound positions. Large overlapping areas rather were observed for the three sound stimuli, located in the temporal, parietal and frontal cortices of both hemispheres. This result argues for the idea of a widely distributed bilateral network accessing an internal representation of the body to encode stimulus position in relation to the body median plane. However, two areas (right BA 40 and left BA 37) also were found to have preferences for sound position. In particular, BA 40 turned out to be significantly more activated by processing central positions, compared to eccentric stimuli. In line with previous findings on visual perception, the latter observation supports the assumption that the right inferior parietal cortex may be preferentially involved in the perception of central stimulus positions in relation to the body.

Enhanced self-localization by auditory cues in blind humans

Purpose. Investigate the involvement of auditory spatial compensation, which is observed in blind humans, in self-localization processes.Method. Sighted and early-blind subjects had to indicate, on a two-dimensional view of the experimental room, the position where they previously sat and had passively listened to auditory spatial cues. Two different environments were distinguished. In a first session, auditory cues (i.e., white broadband sounds) were displayed successively in a dark anechoic room. This condition was defined as a simple acoustic environment. In a second session, four different auditory cues were displayed simultaneously at regular intervals in an experimental room, where echo cues were salient. This condition, which is more reminiscent of the natural situation, was described as a complex acoustic environment.Results. Self-localization capacities were significantly better in early-blind individuals than in sighted subjects, whatever the type of acoustic environment.Conclusions. Auditory compensation leads to improved self-localization capacities in early-blind humans and indicates that prior visual experience is not essential for the development of spatial competence.

Comparing Effects of 2-D and 3-D Visual Cues During Aurally Aided Target Acquisition

The aim of the present study was to investigate interactions between vision and audition during a visual target acquisition task performed in a virtual environment. In two experiments, participants were required to perform an acquisition task guided by auditory and/or visual cues. In both experiments the auditory cues were constructed using virtual 3-D sound techniques based on nonindividualized head-related transfer functions. In Experiment 1 the visual cue was constructed in the form of a continuously updated 2-D arrow. In Experiment 2 the visual cue was a nonstereoscopic, perspective-based 3-D arrow. The results suggested that virtual spatial auditory cues reduced acquisition time but were not as effective as the virtual visual cues. Experiencing the 3-D perspective-based arrow rather than the 2-D arrow produced a faster acquisition time not only in the visually aided conditions but also when the auditory cues were presented in isolation. Suggested novel applications include providing 3-D nonstereoscopic, perspective-based visual information on radar displays, which may lead to a better integration with spatial virtual auditory information.

Does the Perceived Urgency of Auditory Signals Affect Auditory Spatial Cueing in Visual Search Tasks?

In the auditory warning literature, investigators have identified acoustic parameters such as harmonicity and interpulse interval that affect perceived urgency of a warning sound. In the present investigation, we asked whether these parameters would affect visual orienting in a visual search task. Participants located and identified visual targets in a large cluttered search field. Audio cues to the target were also presented. In baseline conditions, auditory cues varying in perceived urgency were presented alone, and the time required to identify the visual target was measured. In the paired-cue conditions, two audio cues were presented, one valid and one invalid. Cue informativeness and cue urgency were manipulated. Performance interference was measured as the difference in search latencies between the informative cue and the corresponding cue in the baseline condition. Although baseline search latencies were not affected by perceived urgency in the baseline conditions, perceived urgency did affect the amount of interference produced by uninformative cues in the paired-cued conditions

Optimal neural population coding of an auditory spatial cue.

A sound, depending on the position of its source, can take more time to reach one ear than the other. This interaural (between the ears) time difference (ITD) provides a major cue for determining the source location. Many auditory neurons are sensitive to ITDs, but the means by which such neurons represent ITD is a contentious issue. Recent studies question whether the classical general model (the Jeffress model) applies across species. Here we show that ITD coding strategies of different species can be explained by a unifying principle: that the ITDs an animal naturally encounters should be coded with maximal accuracy. Using statistical techniques and a stochastic neural model, we demonstrate that the optimal coding strategy for ITD depends critically on head size and sound frequency. For small head sizes and/or low-frequency sounds, the optimal coding strategy tends towards two distinct sub-populations tuned to ITDs outside the range created by the head. This is consistent with recent observations in small mammals. For large head sizes and/or high frequencies, the optimal strategy is a homogeneous distribution of ITD tunings within the range created by the head. This is consistent with observations in the barn owl. For humans, the optimal strategy to code ITDs from an acoustically measured distribution depends on frequency; above 400 Hz a homogeneous distribution is optimal, and below 400 Hz distinct sub-populations are optimal.

Hearing in three dimensions

One of the key functions of hearing is to help us monitor and orient to events in our environment (including those outside the line of sight). The ability to compute the spatial location of a sound source is also important for detecting, identifying, and understanding the content of a sound source, especially in the presence of competing sources from other positions. Determining the spatial location of a sound source poses difficult computational challenges; however, we perform this complex task with proficiency, even in the presence of noise and reverberation. This tutorial will review the acoustic, psychoacoustic, and physiological processes underlying spatial auditory perception. First, the tutorial will examine how the many different features of the acoustic signals reaching a listener’s ears provide cues for source direction and distance, both in anechoic and reverberant space. Then we will discuss psychophysical studies of three-dimensional sound localization in different environments and the basic neural mechanisms by which spatial auditory cues are extracted. Finally, ‘‘virtual reality’’ approaches for simulating sounds at different directions and distances under headphones will be reviewed. The tutorial will be structured to appeal to a diverse audience with interests in all fields of acoustics and will incorporate concepts from many areas, such as psychological and physiological acoustics, architectural acoustics, and signal processing.