Minimum Audible Movement Angle Research Articles

Static and moving minimum audible angle: Independent contributions of reverberation and position.

Two measures of auditory spatial resolution, the minimum audible angle and the minimum audible movement angle, have been obtained in a simulated acoustic environment using Ambisonics sound field reproduction. Trajectories were designed to provide no reliable cues for the spatial discrimination task. Larger threshold angles were found in reverberant compared to anechoic conditions, for stimuli on the side compared to the front, and for moving compared to static stimuli. The effect of reverberation appeared to be independent of the position of the sound source (same relative threshold increase) and was independently present for static and moving sound sources.

Synchronized Automatic Gain Control in Bilateral Cochlear Implant Recipients Yields Significant Benefit in Static and Dynamic Listening Conditions.

Individuals with bilateral cochlear implants (BiCIs) rely mostly on interaural level difference (ILD) cues to localize stationary sounds in the horizontal plane. Independent automatic gain control (AGC) in each device can distort this cue, resulting in poorer localization of stationary sound sources. However, little is known about how BiCI listeners perceive sound in motion. In this study, 12 BiCI listeners’ spatial hearing abilities were assessed for both static and dynamic listening conditions when the sound processors were synchronized by applying the same compression gain to both devices as a means to better preserve the original ILD cues. Stimuli consisted of band-pass filtered (100–8000 Hz) Gaussian noise presented at various locations or panned over an array of loudspeakers. In the static listening condition, the distance between two sequentially presented stimuli was adaptively varied to arrive at the minimum audible angle, the smallest spatial separation at which the listener can correctly determine whether the second sound was to the left or right of the first. In the dynamic listening condition, participants identified if a single stimulus moved to the left or to the right. Velocity was held constant and the distance the stimulus traveled was adjusted using an adaptive procedure to determine the minimum audible movement angle. Median minimum audible angle decreased from 17.1° to 15.3° with the AGC synchronized. Median minimum audible movement angle decreased from 100° to 25.5°. These findings were statistically significant and support the hypothesis that synchronizing the AGC better preserves ILD cues and results in improved spatial hearing abilities. However, restoration of the ILD cue alone was not enough to bridge the large performance gap between BiCI listeners and normal-hearing listeners on these static and dynamic spatial hearing measures.

Скрининговый метод оценки пространственной и временной разрешающей способности слуха при локализации движения по азимутальной координате

A screening method for assessment of spatial and temporal resolution of the auditory system in case of azimuthal movement localization has been suggested and approbated in this paper. An approach of free-field sound source movement modeling was chosen. It is based on change of volume balance of wideband noise bursts on two loudspeakers, placed in front of the subject and separated by 60o azimuthal angle. An assessment of minimum audible movement angles and temporal thresholds for moving sound images was performed with the usage of an adaptive psychoacoustic procedure in ranges of velocities and trajectories of sound images the hearing system most sensitive to. The assessment was performed with participation of 11 healthy adult subjects for two types of signals: 1) control signals with flat spectrum and 2) signals with the reduced fraction of high-frequencies which corresponded to moderate sensorineural hearing loss. Minimum audible movement angles were 1.3o in average, and individual temporal thresholds did not exceed 0.1 s. Both these values did not depend on spectral profile of the signals. The time for assessment of one threshold was about 1.5 minutes. Preliminary approbation of the method suggested by us on the group of six patients with sensorineural hearing loss revealed a several times increase of temporal thresholds in comparison with the same thresholds for normally hearing subjects. Duration of the experiment for assessment of one threshold for patients did not differ from subjects with normal hearing. Thus, the suggested method allows quick assessment of spatial hearing condition in both healthy subjects and patients with hearing loss.

The role of self-motion processing in impairments of the spatial perception of auditory scenes

Natural auditory scenes typically include some motion. When this motion is the result of a moving listener, as is often the case, an accurate spatial percept requires that the listener be able to: 1) determine sound source location over time, 2) determine the extent and characteristics of his/her own motion, and 3) integrate these two pieces of information together. We assembled a battery of tests to evaluate these three criteria in normal, hearing-impaired, and balance-impaired listeners. The battery consists of a dynamic visual acuity test to estimate the listener’s self-motion processing, a measure of the minimum audible movement angle to determine source-motion acuity, and an adapted version of a previously published dynamic front/back illusion to examine the ability to combine self and sound-source motion. We found that listeners with potential vestibular impairment were more likely to have larger differences between source-motion acuity and self-motion integration acuity. This finding and the observ...

Relative head angle and eye position drive systematic distortions in the perception of auditory space

The minimum audible movement angle (MAMA) increases as a function of azimuth. This study examined a potential consequence of this: if this change in resolution across azimuth is not perceptually compensated for it would suggest that a sound rotating at a constant angular velocity around the head would not appear to do so but would appear to move faster at the front than at the side. We therefore examined whether the azimuth of two signals affects their point of subjective similarity for motion. We found that equal movement from two different azimuths is not judged as being equivalent: signals centered at 90° must move at least twice as much as ones centered at 0° to be judged as moving the same amount. Signals centered at 45° were also perceived in a proportionally distorted manner. Furthermore, in some listeners, this expansion/contraction of auditory space appears to shift systematically with eye position. These interactions suggest that the MAMA may not be simply a measure of acuity, but also reflects an underlying head- and eye-driven nonlinear perceptual organization of space, one we term the “equivalent arc,” in which an absolute number of degrees does not correspond to a consistent perceptual unit across azimuth.

The Effects of Hearing Impairment, Age, and Hearing Aids on the Use of Self-Motion for Determining Front/Back Location.

There are two cues that listeners use to disambiguate the front/back location of a sound source: high-frequency spectral cues associated with the head and pinnae, and self-motion-related binaural cues. The use of these cues can be compromised in listeners with hearing impairment and users of hearing aids. To determine how age, hearing impairment, and the use of hearing aids affect a listener's ability to determine front from back based on both self-motion and spectral cues. We used a previously published front/back illusion: signals whose physical source location is rotated around the head at twice the angular rate of the listener's head movements are perceptually located in the opposite hemifield from where they physically are. In normal-hearing listeners, the strength of this illusion decreases as a function of low-pass filter cutoff frequency, this is the result of a conflict between spectral cues and dynamic binaural cues for sound source location. The illusion was used as an assay of self-motion processing in listeners with hearing impairment and users of hearing aids. We recruited 40 hearing-impaired participants, with an average age of 62 yr. The data for three listeners were discarded because they did not move their heads enough during the experiment. Listeners sat at the center of a ring of 24 loudspeakers, turned their heads back and forth, and used a wireless keypad to report the front/back location of statically presented signals and of dynamically moving signals with illusory locations. Front/back accuracy for static signals, the strength of front/back illusions, and minimum audible movement angle were measured for each listener in each condition. All measurements were made in each listener both aided and unaided. Hearing-impaired listeners were less accurate at front/back discrimination for both static and illusory conditions. Neither static nor illusory conditions were affected by high-frequency content. Hearing aids had heterogeneous effects from listener to listener, but independent of other factors, on average, listeners wearing aids exhibited a spectrally dependent increase in "front" responses: the more high-frequency energy in the signal, the more likely they were to report it as coming from the front. Hearing impairment was associated with a decrease in the accuracy of self-motion processing for both static and moving signals. Hearing aids may not always reproduce dynamic self-motion-related cues with sufficient fidelity to allow reliable front/back discrimination.

Hearing motion in motion

The acoustic cues to auditory space are referenced to the head which moves through the world, itself composed of moving sources so that our sensation convolves source with self- motion. With the head still, velocity discrimination, a perceptual process, is related to static acuity via the minimum audible movement angle (MAMA). Yet, while we can accurately localize static sounds, we are much less sensitive to velocity, resorting to distance and time cues where available. Interestingly, when velocity changes as a step function, discrimination thresholds and the amount of post-transition stimulus required for detection is greater than the corresponding MAMA. This suggests that when the head is stationary, the window of temporal integration may vary according to the sound's velocity characteristics. We also have evidence that auditory representational momentum scales with velocity, not duration or distance. Facing and following a moving auditory source is an ecologically important behavior. Tracking exhibits ...

Ventral and dorsal visual pathways support auditory motion processing in the blind: evidence from electrical neuroimaging

Blindness induces processes of neural plasticity, resulting in recruitment of the deafferentated visual areas for non-visual sensory functions. These processes are related to superior abilities of blind compared with sighted individuals for specific auditory and tactile tasks. Recently, an exceptional performance of the blind has been demonstrated for auditory motion perception, with a minimum audible movement angle that was half that of sighted controls (J. Lewald (2013) Neuropsychologia, 51, 181-186). The present study revealed an electrophysiological correlate of this finding by analysing the so-called motion-onset response, a prominent auditory-evoked potential to the onset of motion. The cN1 component of this response, appearing about 170ms after motion onset, was two times higher in amplitude for blind compared with matched sighted control subjects. At the time of the cN1, electrical neuroimaging using sLORETA revealed stronger activation in blind than sighted subjects primarily in ventral visual areas (V1v, V2v, VP, V4v) of the right occipital lobe. Activation was also obtained in middle temporal area V5. These findings suggest that blindness results in stronger involvement of both non-motion areas of the ventral visual stream and motion areas of the dorsal visual stream in processing of auditory motion at the same point in time after motion onset. This argues against the view that visual motion areas, such as area V5, are preferentially recruited for auditory motion analysis in the blind. Rather, cross-modal reorganization of cortical areas induced by blindness seems to be largely independent of the specific visual functions of the same areas in sighted persons.

Exceptional ability of blind humans to hear sound motion: Implications for the emergence of auditory space

Blind people may compensate for their visual loss by the increased use of auditory spatial information, thus showing normal or even supra-normal ability to localize sources of sound. However, the problem of how blind persons develop and maintain an internal concept of the topography of the auditory space in the absence of calibration by visual information is still unsolved. The present study demonstrated a substantial superiority of blind subjects in perception of auditory motion: The minimum audible movement angle of blind subjects (mean 3°) was about half the value found in matched sighted controls, whereas no such advantage was demonstrable for localization of stationary sound. There were no significant differences between early or congenitally blind subjects and late blind subjects, suggesting that long-term visual deprivation per se, independently of the point in time of its onset, was relevant for the superiority in auditory motion perception. The results were compatible with the hypothesis that in the absence of visual input the calibration of the auditory space is performed by audiomotor feedback, that is, by the evaluation of systematic changes of auditory spatial cues resulting from head and body movements. It is reasonable to assume that with blindness the neuronal circuits specifically concerned with the analysis of auditory motion are more intensely trained than in sighted people. It seems possible that the higher demand of motion analysis associated with blindness is related to processes of reorganization in the brain, as have been previously reported to occur also in areas known to be involved in auditory and/or visual motion analysis in sighted persons.

Absence of compensation for vestibular-evoked passive head rotations in human sound localization

A world-fixed sound presented to a moving head produces changing sound-localization cues, from which the audiomotor system could infer sound movement relative to the head. When appropriately combined with self-motion signals, sound localization remains spatially accurate. Indeed, free-field orienting responses fully incorporate intervening eye-head movements under open-loop localization conditions. Here we investigate the default strategy of the audiomotor system when localizing sounds in the absence of efferent and proprioceptive head-movement signals. Head- and body-restrained listeners made saccades in total darkness toward brief (3, 10 or 100 ms) broadband noise bursts, while being rotated sinusoidally (f=1/9 Hz, V(peak) =112 deg/s) around the vertical body axis. As the loudspeakers were attached to the chair, the 100 ms sounds might be perceived as rotating along with the chair, and localized in head-centred coordinates. During 3 and 10 ms stimuli, however, the amount of chair rotation remained well below the minimum audible movement angle. These brief sounds would therefore be perceived as stationary in space and, as in open-loop gaze orienting, expected to be localized in world-centred coordinates. Analysis of the saccades shows, however, that all stimuli were accurately localized on the basis of imposed acoustic cues, but remained in head-centred coordinates. These results suggest that, in the absence of motor planning, the audio motor system keeps sounds in head-centred coordinates when unsure about sound motion relative to the head. To that end, it ignores vestibular canal signals of passive-induced head rotation, but incorporates intervening eye displacements from vestibular nystagmus during the saccade-reaction time.

Effects of velocity and motion-onset delay on detection and discrimination of sound motion

The effect of velocity on auditory motion processing in combination with a motion-onset delay was investigated in two experiments. The detection of motion onset and discrimination of motion direction were studied, employing a psychophysical reaction time task. Listeners were presented with sounds moving along the frontal horizontal plane in a dark anechoic environment. Response times (RTs) were measured, while the velocity (20°/s, 40°/s, 80°/s) and the motion-onset delay (the time between sound onset and start of motion: 0, 200, 500, 1000 ms) were varied. Listeners responded faster with higher velocity and longer motion-onset delay. In particular, with higher velocity, the function relating RT to motion-onset delay had a steeper initial decrease than with lower velocities. The results are in line with psychophysical studies of the minimum audible movement angle and recent electrophysiological data about the role of motion velocity in auditory motion processing. The effect of motion-onset delay is discussed with regard to a dynamic temporal window, in which auditory spatial information is integrated until enough information is accumulated to trigger motion detection.

Auditory resolution in virtual environments: Effects of spatialization algorithm, off‐center listener positioning and speaker configuration

We present the results of an empirical study on the effects of room and off‐center listener positioning on sound localization in two virtual environments, VBAP and Ambisonics. Localization accuracy has been assessed by estimating Minimum Audible Angles and Minimum Audible Movement Angles for the two spatialization algorithms and for three directions of sound incidence, in the studio and a concert hall for listeners in off‐center listener positions, with two loudspeaker setups. A model of localization accuracy as a function of the experimental variables is presented, that can be used to quantify the effects of the room and off‐center listening positions on sound localization and auditory movement detection.

Localizing Sound Sources in a CAVE-Like Virtual Environment with Loudspeaker Array Reproduction

In a CAVE-like virtual environment spatial audio is typically reproduced with amplitude panning on loudspeakers behind the screens. We arranged a localization experiment where the subjects' task was to point to the perceived location of a sound source. Measured accuracy for a static source was as good as the accuracy in previous headphone experiments using head-related transfer functions. We also measured the localization accuracy of a moving auditory stimulus. The accuracy was decreased by an amount comparable to the minimum audible movement angle.

Auditory spatial resolution in horizontal, vertical, and diagonal planes.

Minimum audible angle (MAA) and minimum audible movement angle (MAMA) thresholds were measured for stimuli in horizontal, vertical, and diagonal (60 degrees) planes. A pseudovirtual technique was employed in which signals were recorded through KEMAR's ears and played back to subjects through insert earphones. Thresholds were obtained for wideband, high-pass, and low-pass noises. Only 6 of 20 subjects obtained wideband vertical-plane MAAs less than 10 degrees, and only these 6 subjects were retained for the complete study. For all three filter conditions thresholds were lowest in the horizontal plane, slightly (but significantly) higher in the diagonal plane, and highest for the vertical plane. These results were similar in magnitude and pattern to those reported by Perrott and Saberi [J. Acoust. Soc. Am. 87, 1728-1731 (1990)] and Saberi and Perrott [J. Acoust. Soc. Am. 88, 2639-2644 (1990)], except that these investigators generally found that thresholds for diagonal planes were as good as those for the horizontal plane. The present results are consistent with the hypothesis that diagonal-plane performance is based on independent contributions from a horizontal-plane system (sensitive to interaural differences) and a vertical-plane system (sensitive to pinna-based spectral changes). Measurements of the stimuli recorded through KEMAR indicated that sources presented from diagonal planes can produce larger interaural level differences (ILDs) in certain frequency regions than would be expected based on the horizontal projection of the trajectory. Such frequency-specific ILD cues may underlie the very good performance reported in previous studies for diagonal spatial resolution. Subjects in the present study could apparently not take advantage of these cues in the diagonal-plane condition, possibly because they did not externalize the images to their appropriate positions in space or possibly because of the absence of a patterned visual field.

Minimum dynamic lateralization for multiple moving sources

It is still unresolved whether auditory motion is perceived via specialized motion detectors or inferred from static samples of changes in spatial position. This question has been investigated by comparing minimum audible movement angles for single sources moving discretely or continuously [Perrott and Marlborough, J. Acoust. Soc. Am. 85, 1773–1775 (1989)]. But using one source does not force the listener to determine movement by only one of the aforementioned processes. To better measure sensitivity to pure auditory dynamics, the following study simulates multiple overlapping sources moving in the same direction across random sections of the auditory hemifield. Experimental stimuli are composed of different portions of the trajectories of circling resonant sources, which are individually created by dynamically varying interaural time and level differences. The multiple, variable endpoints in the composite stimulus should inhibit the listener from relying solely on such cues to determine movement direction. Pilot studies using from 1–5 concurrent sources show dynamic lateralization thresholds are lowest for one moving source. This implies movement is best perceived when stimulus endpoints can be sampled. However, thresholds across multiple sources do not significantly differ regardless of number, which may represent a measure of sensitivity to pure auditory dynamics.

Minimum audible movement angle in vertical, horizontal, and oblique planes: Effects of velocity and frequency content

Minimum audible movement angles (MAMAs) were measured employing a pseudo-virtual method of stimulus presentation. All stimuli were digitally recorded through KEMAR’s two ears while he was positioned in an anechoic chamber with moving loudspeakers presenting sounds in one of seven planes: frontal horizontal, lateral horizontal, median sagittal, lateral vertical, or one of three different oblique planes. These recorded binaural stimuli were subsequently played through insert earphones to subjects seated in a darkened sound-insulated room. Subjects had to say on each trial whether a single moving sound moved ‘‘left’’ or ‘‘right’’ (‘‘up’’ or ‘‘down;’’ ‘‘front’’ or ‘‘back’’). With velocity held constant during a run (from 0 to 180°/s), stimulus duration was varied adaptively to track the MAMA threshold. Stimuli were Gaussian noise bursts that were either wideband, 4-kHz low-passed, or 4-kHz high-passed. Results will be discussed in terms of human sensitivity at low and high frequencies to dynamic information provided primarily by (1) changing interaural difference cues (frontal horizontal plane); (2) changing spectral cues (median vertical plane); and (3) combinations of changing interaural and spectral cues. [Work supported by NIDCD.]

The impact of system latency on dynamic performance in virtual acoustic environments

Engineering constraints that may be encountered when implementing interactive virtual acoustic displays are examined. In particular, system parameters such as the update rate and total system latency are defined and the impact they may have on perception is discussed. For example, examination of the head motions that listeners used to aid localization in a previous study suggests that some head motions may be as fast as about 175°/s for short time periods. Analysis of latencies in virtual acoustic environments (VAEs) suggests that: (1) commonly specified parameters such as the audio update rate determine only the best-case latency possible in a VAE, (2) total system latency and individual latencies of system components, including head-trackers, are frequently not measured by VAE developers, and (3) typical system latencies may result in undersampling of relative listener-source motion of 175°/s as well as positional instability in the simulated source. To clearly specify the dynamic performance of a particular VAE, users and developers need to make measurements to average system latency, update rate, and their variability using standardized rendering scenarios. Psychoacoustic parameters such as the minimum audible movement angle can then be used as target guidelines to assess whether a given system meets perceptual requirements.

Minimum audible angle and minimum audible movement angle in the median sagittal plane as a function of stimulus spectrum and reference elevation

Minimum audible angle (MAA) and minimum audible movement angle (MAMA) were measured employing a pseudo-virtual method of stimulus presentation. All stimuli were digitally recorded through KEMAR’s two ears while he was positioned in an anechoic chamber with fixed and moving loudspeakers presenting sounds in his median sagittal plane; these recorded binaural stimuli were subsequently played through insert earphones to subjects seated in a darkened sound-insulated room. For the measurement of MAA, subjects had to say which of two stationary 300-ms sounds was higher in elevation; for the measurement of MAMA, subjects had to say whether a single moving sound moved up or down. Velocities in the MAMA experiment ranged from 20°/s to 150°/s. Stimuli were Gaussian noise bursts that were either wide band, 4-kHz low passed, or 4-kHz high passed. Reference elevation was either 0° or 45° elevation. Results will be discussed in terms of static and dynamic pinna cues that underlie elevation discrimination for high-frequency stimuli and the possible shoulder-bounce cue that may enable elevation discrimination for low-frequency stimuli. [Work supported by NIDCD 00185.]

Minimum audible movement angle thresholds at low velocities

Auditory resolution of a moving sound source was determined in a real motion paradigm. Minimum audible movement angle (MAMA) and minimum visible movement angle (MVMA) thresholds were obtained for five subjects in a two-alternative, forced-choice, three-up/one-down, adaptive procedure as a function of velocity. Velocities from 0.15°/s to 40°/s were utilized to give a wide range of motion thresholds. The low-ended velocities are of particular interest because in a previous study Saberi and Perrott showed an increase of approximately 4–5 deg for velocities below 1°/second indicating a U-shaped function in the detection of MAMA thresholds [Saberi and Perrott, J. Acoust. Soc. Am. 88, 2639–2644 (1990)]. The results of the current study suggest that MAMA thresholds flatten or decrease for velocities below 1°/s. However, it should be noted that in the current study, real motion was employed in contrast to that of simulated motion which utilized a 1.8-ms click train with 5.7-cm speakers in the Saberi and Perrott study. In addition, when MAMA and MVMA thresholds are compared at the lowest velocities, MAMA thresholds are at or below MVMA thresholds. Implications of results will be discussed. [Work supported by NSF (BNS-9025118).]

Minimum audible movement angle as a function of the azimuth and elevation of the source.

In the future auditory directional cues may enhance situational awareness in cockpits with head-coupled displays. This benefit would depend, however, on the pilot's ability to detect the direction of moving sounds at different locations in space. The present investigation examined this ability. Auditory motion acuity was measured by the minimum audible movement angle (MAMA): the minimum angle of travel required for detection of the direction of sound movement. Five experienced listeners were instructed to indicate the direction of travel of a sound source (broadband noise at 50 dBA) that moved at a velocity of 20 deg/s. Nine azimuth positions were tested at 0 deg elevation. Five elevations were then tested at 0 deg azimuth. Finally two azimuth positions were tested at an elevation of 80 deg. The position of the source did not significantly affect the MAMA for azimuth locations between +40 and -40 deg and elevations below 80 deg. Within this area the MAMA ranged between 1 and 2 deg. Outside this area the MAMA increased to 3 to 10 deg.