Auditory displays ..the purpose of the ears is to point the eyes Georg von B k sy

1. 1 Auditory displays�..the purpose of the ears is to point the eyes� Georg von B�k�sy Carolina Figueroa University of Idaho Advanced Human Factors

2. 2 Content 1. Ability to detect the direction of moving sounds at different locations in space 2. Is simulation of virtual sound sources accurate? 3. Acoustic and non-acoustic factors that contribute to distance perception of sound sources 4. Effects on detection of signals elevation and position when the signal bandwidth is limited

3. 3 Psychoacoustics tutorial : http://interface.cipic.ucdavis.edu/CIL_tutorial/3D_home.htm

4. 4 - 1/4 - Minimum Audible Movement Angle (MAMA) as a Function of the Azimuth and Elevation of the Source By Thomas Z. Strybel, Carol L. Manligas, David R. Perrott, 1992

5. 5 Uses of auditory spatial information in head-coupled display systems: Moving head and eyes to identify objects or events Reduction in visual search time (150 ms 10deg of central visual area) Greatest benefit when targets located at peripheral visual areas Enhance situational awareness of pilot Example: warning of a target when pilot is not looking Uses: Provides natural means of directing the head and eyes of the pilot to important events in his or her environment. Researchers (Perrot 1998, Saberi, Brown, and Strybel, 1990) measured a reduction in visual search time produced by the addition of auditory directional information (100/150 ms reduction from 700 ms, when auditory stimuli and target where presented on the same location) The magnitude of the effect depend on the location of the visual target, with the greatest benefit found for targets located in peripheral visual areas. Doll, Gerth, Engelman, and Folds (1986) suggested that simulated auditory directional cues could be used to enhance the situational awareness of the pilot. For example: the display could warn the pilot of an object or any other danger situation when he is not looking at it directly. This enhancement depends on the 1) Fidelity of the simulation technique and 2) the ability of the pilot. Uses: Provides natural means of directing the head and eyes of the pilot to important events in his or her environment. Researchers (Perrot 1998, Saberi, Brown, and Strybel, 1990) measured a reduction in visual search time produced by the addition of auditory directional information (100/150 ms reduction from 700 ms, when auditory stimuli and target where presented on the same location) The magnitude of the effect depend on the location of the visual target, with the greatest benefit found for targets located in peripheral visual areas. Doll, Gerth, Engelman, and Folds (1986) suggested that simulated auditory directional cues could be used to enhance the situational awareness of the pilot. For example: the display could warn the pilot of an object or any other danger situation when he is not looking at it directly. This enhancement depends on the 1) Fidelity of the simulation technique and 2) the ability of the pilot.

6. 6 How effective is the simulation of 3D auditory cues? Auditory localization (accuracy of localization) Auditory spatial acuity (discrimination) Other studies have reported data on human auditory localization and spatial acuity but� static sounds located in the horizontal plane that intersects the interaural axis. This article is focused on the effectiveness of simulated 3D auditory cues that depend on 1) auditory localization = pilot�s accuracy to determine the location of a sound and 2) auditory spatial acuity = pilot�s ability to discriminate between the positions of 2 simultaneous sounds sources There are many published reports on human auditory localization and spatial acuity, most of them are focused on the localization of STATIC sounds located in the HORIZONTAL plane that intersects the inter-aural axis. This article is focused on the effectiveness of simulated 3D auditory cues that depend on 1) auditory localization = pilot�s accuracy to determine the location of a sound and 2) auditory spatial acuity = pilot�s ability to discriminate between the positions of 2 simultaneous sounds sources There are many published reports on human auditory localization and spatial acuity, most of them are focused on the localization of STATIC sounds located in the HORIZONTAL plane that intersects the inter-aural axis.

7. 7 Other reports� Localization and acuity are best for sounds located: Directly in front of the subject (0 deg azimuth) Poorest in the area directly opposite each ear (+/- 90 deg azimuth) Stevens and Newman (1936) Mills(1972) Spatial Acuity: assessed by minimum audible angle (MAA) Findings of this other reports are that: for sources located in the horizontal plane, localization and acuity are best for sounds located Directly in front of the subject (0 deg azimuth) Poorest in the area directly opposite each ear (+/- 90 deg azimuth) Auditory spatial acuity has been assessed by the Minimum Audible Angle (MAA) which is he smallest separation between two sources that can be reliably detected. Mills (1972) determined that MAA was smallest (1 deg) for sources located at 0 deg azimuth and increased to 40 deg at 90 deg azimuthFindings of this other reports are that: for sources located in the horizontal plane, localization and acuity are best for sounds located Directly in front of the subject (0 deg azimuth) Poorest in the area directly opposite each ear (+/- 90 deg azimuth) Auditory spatial acuity has been assessed by the Minimum Audible Angle (MAA) which is he smallest separation between two sources that can be reliably detected. Mills (1972) determined that MAA was smallest (1 deg) for sources located at 0 deg azimuth and increased to 40 deg at 90 deg azimuth

8. 8 This investigation� .. Uses dynamic acoustic events� Acoustic events are likely to be moving The pilot�s head would be free to move Aircraft would be moving too Factors taken into account� Variations in azimuth (right / left) Variations in elevation (up / down) MAMA: minimum angle of travel required for detection of the direction of movement of a sound source (Perrot and Tucker 1988) MAA: Static auditory spatial acuity There is little data about the ability of a listener to utilize auditory spatial information under dynamic listening conditions. Most data are based on only ONE location (0 deg azimuth � horizontal plane) Index of auditory spatial resolution of dynamic acoustic events : MAMA MAMA = Minimum Audible Movement Angle MAA = Static Auditory Spatial Acuity MAMA There is little data about the ability of a listener to utilize auditory spatial information under dynamic listening conditions. Most data are based on only ONE location (0 deg azimuth � horizontal plane) Index of auditory spatial resolution of dynamic acoustic events : MAMA MAMA = Minimum Audible Movement Angle MAA = Static Auditory Spatial Acuity MAMA

9. 9 Only two investigations� Grantham, 1986 One stimulus Tested on large number of source positions Harris & Sergeant, 1971 Several stimulus On two source positions Findings : Ability to localize position of a sound source under dynamic conditions is limited � There only two investigations about dynamic acuity for source locations (other than 0 deg azimuth) Grantham 1986, Harris & Sergeant, 1971. And these two differed in their emphasis: Grantham = used only one stimulus and tested a large number of source positions. These two studies indicates that knowledge of the human listener�s ability to localize the position of a sound source under dynamic conditions is limited.There only two investigations about dynamic acuity for source locations (other than 0 deg azimuth) Grantham 1986, Harris & Sergeant, 1971. And these two differed in their emphasis: Grantham = used only one stimulus and tested a large number of source positions. These two studies indicates that knowledge of the human listener�s ability to localize the position of a sound source under dynamic conditions is limited.

10. 10 Method MAMA�s measured +/- 80 deg azimuth Elevation between 0 and 87.5 deg Subjects 5 experienced subjects on MAMA tasks Method Test conducted in a large audiometric test chamber Subjects were seated in the center of the room. Subject�s head position was fixed The purpose of the investigation was to examine auditory spatial ability under dynamic listening conditions representatives of conditions encountered in head coupled display systems. MAMA�s were measure for sound sources located between +80 and -80 deg azimuth and for elevations between 0 and 87.5 deg relative to the horizontal plane. Subjects: 5 experienced subjects performing MAMA tasks Method: subjects were seated in the center of the room where there was a semicircular aluminum sound boom (360 degree circle, 1 m diameter) Elevation of sound boom was in her interaural axis in the horizontal plane Subject�s head position was fixed by a chin rest. The purpose of the investigation was to examine auditory spatial ability under dynamic listening conditions representatives of conditions encountered in head coupled display systems. MAMA�s were measure for sound sources located between +80 and -80 deg azimuth and for elevations between 0 and 87.5 deg relative to the horizontal plane. Subjects: 5 experienced subjects performing MAMA tasks Method: subjects were seated in the center of the room where there was a semicircular aluminum sound boom (360 degree circle, 1 m diameter) Elevation of sound boom was in her interaural axis in the horizontal plane Subject�s head position was fixed by a chin rest.

11. 11 Method At 0 deg elevation loudspeaker mounted on the horizontal boom Above elevations loudspeaker mounted vertically MAMA measured at a total of 16 azimuth-elevation combinations Constant velocity of moving source 20 deg/s Testing in the dark Adaptive psychophysical use to measured MAMA�s MAMA measured at 16 azimuth-elevation combinations: Azimuth: 0, 10, 20, 40, 80, -10, -20, -40, -80 Elevations: 56, 70, 80, 85, 87.5 Velocity was constant 20 deg/s and the length of the sound was determined by the duration of the stimulus. Subjects were asked to indicate if the sound traveled toward their left or right ear by pushing a button in a computer. Testing was done in the dark so the subject couldn�t see the sound boom moving Adaptive psychophysical use to measured MAMA�s, use to measure thresholds where the stimulus level on any trial is determined by the previous stimulus and response. When the subject identified the correct or incorrect direction the stimulus durations was decreased or increased 10%MAMA measured at 16 azimuth-elevation combinations: Azimuth: 0, 10, 20, 40, 80, -10, -20, -40, -80 Elevations: 56, 70, 80, 85, 87.5 Velocity was constant 20 deg/s and the length of the sound was determined by the duration of the stimulus. Subjects were asked to indicate if the sound traveled toward their left or right ear by pushing a button in a computer. Testing was done in the dark so the subject couldn�t see the sound boom moving Adaptive psychophysical use to measured MAMA�s, use to measure thresholds where the stimulus level on any trial is determined by the previous stimulus and response. When the subject identified the correct or incorrect direction the stimulus durations was decreased or increased 10%

12. 12 Results Findings agree with previous investigations on dynamic and static localization in the horizontal plane, which indicate that performance is best at 0 deg azimuth and is degraded at peripheral source locations. Results indicate that pilot�s awareness of moving events in head-coupled displays systems depend on: Location of the event Velocity of events (in and out) The MAMA ranges from 1 to 3 deg for sources located in a semi elliptical area located in front of the subject. The center of the ellipse is located at 0 deg azimuth and elevation. The major axis of the ellipse would extend in the vertical dimension to 80 deg. The minor axis would extend in the horizontal direction out to +/- 40 deg azimuth. For sources outside this semi elliptical area, the MAMA increases 3 to 10 deg. Dynamic localization was poorest at 80 deg azimuth, 80 deg elevation (10.3 deg). Findings agree with previous investigations on dynamic and static localization in the horizontal plane, which indicate that performance is best at 0 deg azimuth and is degraded at peripheral source locations. Results indicate that pilot�s awareness of moving events in head-coupled displays systems based on auditory information depend on: - the location of the event and also Velocity of those events outside the �elliptical area� that require more time to be detected. In = 50 to 100 ms minimum duration in order to detect the direction of movement Out = 160 ms at 80 deg azimuth and 0 deg elevation to 340 ms at 0 deg azimuth and 87.5 deg elevation The MAMA ranges from 1 to 3 deg for sources located in a semi elliptical area located in front of the subject. The center of the ellipse is located at 0 deg azimuth and elevation. The major axis of the ellipse would extend in the vertical dimension to 80 deg. The minor axis would extend in the horizontal direction out to +/- 40 deg azimuth. For sources outside this semi elliptical area, the MAMA increases 3 to 10 deg. Dynamic localization was poorest at 80 deg azimuth, 80 deg elevation (10.3 deg). Findings agree with previous investigations on dynamic and static localization in the horizontal plane, which indicate that performance is best at 0 deg azimuth and is degraded at peripheral source locations. Results indicate that pilot�s awareness of moving events in head-coupled displays systems based on auditory information depend on: - the location of the event and also Velocity of those events outside the �elliptical area� that require more time to be detected. In = 50 to 100 ms minimum duration in order to detect the direction of movement Out = 160 ms at 80 deg azimuth and 0 deg elevation to 340 ms at 0 deg azimuth and 87.5 deg elevation

13. 13 Results Additional data is required in order to effectively detect moving sounds: MAMA measured at locations below the horizontal plane, Velocity in peripheral locations Actual Moving sounds vs. simulations of moving sounds MAMA must be measured at locations below the horizontal plane, obstacles and threats can be located in any direction relative to the pilot. Velocity (which affects the MAMA at 0 deg azimuth) must be examine at peripheral locations. More data is needed on differences in performance between actual moving sounds and simulations of moving sounds because this is what will be use in the cockpit. MAMA must be measured at locations below the horizontal plane, obstacles and threats can be located in any direction relative to the pilot. Velocity (which affects the MAMA at 0 deg azimuth) must be examine at peripheral locations. More data is needed on differences in performance between actual moving sounds and simulations of moving sounds because this is what will be use in the cockpit.

14. 14 - 2/4 - Fidelity of Three Dimensional-Sound Reproduction Using a Virtual Auditory Display By Erno H. A Langedik and Adelbert W. Bronkhorst 2000

15. 15 Is the simulation of virtual sound sources accurate? Do the real and virtual sound sources generate identical percepts? How to test it? Direct A/B comparison Problem: use of headphone for virtual source, no headphones for real source HRTF�s and HPTF�s affect by removing/replacing of headphones Solution: open transducer (used by Zahorik 1996, Hartmann and Wittenber 1996) Subjects can remove and replace the headphone during trial but they will know when is real and virtual, besides this HRTF and HPTF can be affected by head movements (when removing and replacing headphones) and also the interval between changes.Subjects can remove and replace the headphone during trial but they will know when is real and virtual, besides this HRTF and HPTF can be affected by head movements (when removing and replacing headphones) and also the interval between changes.

16. 16 2AFC: 2 interval 2 alternative forced choice Listener had to detect the interval with the virtual sound Different filter lengths made difficult the identification of the stimuli Listeners had difficulties with both tasks (yes/no, 2AFC) because discriminating cues if present had to be learned and demanded substantial memorization on the subject, that is why they add a 3rd paradigm = oddball 2AFC: 2 interval 2 alternative forced choice Listener had to detect the interval with the virtual sound Different filter lengths made difficult the identification of the stimuli Listeners had difficulties with both tasks (yes/no, 2AFC) because discriminating cues if present had to be learned and demanded substantial memorization on the subject, that is why they add a 3rd paradigm = oddball

17. 17 1) Virtual sound-source generation Subjects 6 experienced in sound localization listeners Headband with microphone and earphone Listener seated with his head in the center of the loudspeaker arc HRTF measurements carried out for all speaker positions, then headphones were position and HRTF were measured again (investigate influence of the headphones) Acoustical verification measurements were carried out to verify accuracy of wave forms After the 2 set of HRTFs measurements the subjects kept the headphones in position. Acoustical verification First HRTF and HPTF were measured for current loudspeaker position, then virtual headphone filter was calculated The signal was presented over the headphones and recorded by the microphone, after correcting the microphone response then it was compared to the previous HRTF measurement.After the 2 set of HRTFs measurements the subjects kept the headphones in position. Acoustical verification First HRTF and HPTF were measured for current loudspeaker position, then virtual headphone filter was calculated The signal was presented over the headphones and recorded by the microphone, after correcting the microphone response then it was compared to the previous HRTF measurement.

18. 18 1) Virtual sound-source generation Design 6 loudspeaker positions (azimuth, elevation): (-90,-60) (180,-30) (-90, 0) (30,0) (90,30) (0,60) 3 paradigms Yes/No 2AFC: AB or BA (where A is real and B virtual sound) oddball design presented in the 2 or 3rd interval giving 4 possible orders: ABAA, BABB, AABA, BBAB 50 trials per paradigm Real and virtual sources were compared for 6 loudspeakers positions using 3 paradigms For each position the 3 paradigms were presented successively: - yes/no, press if you hear the real or virtual sound source - 2AFC: AB or BA (where A is real and B virtual sound) - oddball design presented in the 2 or 3rd interval giving 4 possible orders: ABAA, BABB, AABA, BBAB For each paradigm 50 trials were presented A headrest helped subjects to retain a fixed head position. Head movements affect virtual sound source, movements of the limbs and torso also can change the acoustic transfer function. Real and virtual sources were compared for 6 loudspeakers positions using 3 paradigms For each position the 3 paradigms were presented successively: - yes/no, press if you hear the real or virtual sound source - 2AFC: AB or BA (where A is real and B virtual sound) - oddball design presented in the 2 or 3rd interval giving 4 possible orders: ABAA, BABB, AABA, BBAB For each paradigm 50 trials were presented A headrest helped subjects to retain a fixed head position. Head movements affect virtual sound source, movements of the limbs and torso also can change the acoustic transfer function.

19. 19 1) Virtual sound-source generation Results Headphone effect on HRTFs Amplitude differences between HRTF�s with and without headphones infront of the ears are within 5 dB for most frequencies. Above 1kHZ frequencies peaks and valleys of the HRTF�s with/without headphone occurred in the same frequencies. Headphones had no effect on the interaural difference in arrival time of the signal Left ear = Upper solid line Right ear = lower solid line HRTF with headphones = solid line HRTF without headphones = broken lines

20. 20 1) Virtual sound-source generation Results cont�d.. Acoustical differences: Differences between real (broken lines) and virtual (solid lines) were very small HRTFs for left � lower line HRTF;s for right � upper line Psychophysical validation results: Yes/no and 2AFC paradigms not significantly Different from chance where it was for the oddball Paradigm. In general the differences between real and virtual free-field HRTF�s were quite small. Psychophysical validation results: It shows that the scores for the yes/no and 2AFC paradigms were not significantly different from chance, where it was for the oddball paradigm. However, the average score in the oddball paradigm (53%) is only slightly above chance. In general the differences between real and virtual free-field HRTF�s were quite small. Psychophysical validation results: It shows that the scores for the yes/no and 2AFC paradigms were not significantly different from chance, where it was for the oddball paradigm. However, the average score in the oddball paradigm (53%) is only slightly above chance.

21. 21 1) Virtual sound-source generation Conclusions: It is possible to accurately reproduce 3-field acoustic waveforms at eardrum. The virtual sound source practically indistinguishable from an actual loudspeaker in the free field These findings are in agreement with previous studies even though there are many methodological differences (such as size of headphones,: Zahorik 1995, Hartmann and Wittenberg 1996)

22. 22 2) Measured vs. Interpolated HRTFs Second experiment: generation of virtual sound sources at positions for which actual HRFTs are not measured. HRTF�s measured for limited source positions with specific algorithms implemented allowing continuous interpolation between positions. How well the intermediate positions are simulated?

23. 23 2) Measured and interpolated HRTF�s. Subjects: 6 listeners with normal hearing (half experienced) Design: 104 loudspeaker positions 25 different sounds (200 Hz � 16 kHz) Filter long enough to include acoustical effects of the body, head, and ears of listener. 3 independent variables: grid resolution: 5, 6 or 11 deg aprox. direction of interpolation: horizontal, vertical or diagonal; amplitude of simtulus 8 Target positions: (0,90) (45,45) (135,45) (0,0) (90,0) (180,0) (45, -45) and (135,-45) Conditions and target positions pooled in 6 blocks 12 trials, 1 interpolation direction, 4 target positions, 2 scrambling cond. And 3 grid resolutions. Oddball paradigm used: A=measured HRTF, B=interpolated HRTF ABAA, BABB, AABA, BBAB Subjects had to detect the interval with the oddball HRTF measured in 104 loudspeaker positions. During measurements subjects were headphones and got feedback when they were off positions (their head) 25 different sounds where randomly choose, the output was filtered with either measured or interpolated HRTF�s and inverse filtered with the HPTF (head phone transfer function) The filters were long enough to account for effects (body, head, and ears of the listener) 3 independent variables: - grid resolution: 5.6, 11.3, 22.5 deg - direction of interpolation: horizontal, vertical or diagonal. For H and V 2 HRTF�s contributed to the interpolation, the loudspeakers for these HRTF differed in grid resolution in azimuth or elevation. In the Diagonal condition there were 4 contributing HRTF, the loudspeakers differed in azimuth, elevation in both directions. - Scrambling of the stimulus: amplitud (0 to +/- 3 dB per 1/3 octave) 8 Target positions Conditions and target positions pooled in 6 blocks 1 block contained all trials for 1 interpolation direction, 4 target positions, 2 scrambling conditions and 3 grid resolutions. Within blocks order of target positions and scrambling conditions was varied Resolution condition presented same order: from low to high 12 trials per condition HRTF measured in 104 loudspeaker positions. During measurements subjects were headphones and got feedback when they were off positions (their head) 25 different sounds where randomly choose, the output was filtered with either measured or interpolated HRTF�s and inverse filtered with the HPTF (head phone transfer function) The filters were long enough to account for effects (body, head, and ears of the listener) 3 independent variables: - grid resolution: 5.6, 11.3, 22.5 deg - direction of interpolation: horizontal, vertical or diagonal. For H and V 2 HRTF�s contributed to the interpolation, the loudspeakers for these HRTF differed in grid resolution in azimuth or elevation. In the Diagonal condition there were 4 contributing HRTF, the loudspeakers differed in azimuth, elevation in both directions. - Scrambling of the stimulus: amplitud (0 to +/- 3 dB per 1/3 octave) 8 Target positions Conditions and target positions pooled in 6 blocks 1 block contained all trials for 1 interpolation direction, 4 target positions, 2 scrambling conditions and 3 grid resolutions. Within blocks order of target positions and scrambling conditions was varied Resolution condition presented same order: from low to high 12 trials per condition

24. 24 2) Measured and interpolated HRTF�s. Results� Same auditory percept for Measured and Interpolated HRTF�s when spatial resolution is approx. 6 deg Acoustical differences = between 1.5 and 2.5 dB ok But > 2.5 dB affect position of the source -> other type of interpolation, cubic spline HRTF for contralateral ear are more that 15dB below amplitudes for the ipsilateral HRTF for frequencies above 3kHz (different findings from Enzel and Foster 1993, �sounds localization no affected by interpolation�, they used non-individual HRTF causing large impact on the localization accuracy that was obscured by interpolation effect) Other studies have tested measured HRTF�s in specific positions, but what about the intermediate positions? HRTF�s for intermediate positions can be calculated using linear interpolation. When spatial resolution is approx. 6 deg, virtual sound sources give the same exactly auditory percept from interpolated and measured HRTF�s When accoustical differences between measured and interpolated HRTF�s are between 1.5 and 2.5 dB per 1/3 octave, this will introduce timbre differences (timbre, cue that is not relevant for sound localization) but if these difference exceeds 2.5 dB this can affect the position of the source. Indicating that a more sophisticated interpolation might be appropriate (cubic splines) Analyzing the relationship between maximum acoustical differences and percentage-correct detection - lower correlation for contralateral ear for which larger interpolation errors occurred than for the ipsilateral ear. Other studies have tested measured HRTF�s in specific positions, but what about the intermediate positions? HRTF�s for intermediate positions can be calculated using linear interpolation. When spatial resolution is approx. 6 deg, virtual sound sources give the same exactly auditory percept from interpolated and measured HRTF�s When accoustical differences between measured and interpolated HRTF�s are between 1.5 and 2.5 dB per 1/3 octave, this will introduce timbre differences (timbre, cue that is not relevant for sound localization) but if these difference exceeds 2.5 dB this can affect the position of the source. Indicating that a more sophisticated interpolation might be appropriate (cubic splines) Analyzing the relationship between maximum acoustical differences and percentage-correct detection - lower correlation for contralateral ear for which larger interpolation errors occurred than for the ipsilateral ear.

25. 25 - 3/4 - Auditory Display of Sound Source Distance By Pavel Zahorik, 2002 How to reproduce sound source distance: acoustical and non-acoustical factors that contribute to perceive distance.

26. 26 Psychophysical research focused on: Source direction (horizontal, vertical) But not in 3rd dimension: source distance This article describes how acoustical and non-acoustical factors contribute to the perception of sound distance. Auditory system provide us with critical information about our environment, it is specially useful in certain conditions where vision is not effective (in the dark, or when we can�t see the object falling but can hear it). Auditory system provide us with critical information about our environment, it is specially useful in certain conditions where vision is not effective (in the dark, or when we can�t see the object falling but can hear it).

27. 27 Intensity: sound intensity decreases as distance between listener and sound source increases. Inverse-square law= 6dB intensity loss for each doubling of distance *ambiguous cue because sound source acoustic power and distance (from listener to sound source) can change Direct-to-Reverberant Energy Ratio: occurs in environments with sound reflecting surfaces the Radio of Energy reaching listener directly vs. the reverberant energy (reflected by surface) decreases if the sound source distance increases Spectrum: at farther distances, the sound absorbing properties of air modify the sound source spectrum by attenuating high frequencies Binaural differences: when listener moves his head, changes in azimuth will be range dependant. For sources that are close, a small shift cause a large change in azimuth, if the source increases distance there is less change in azimuth. Vision: Ventriloquism effect-> cause the perceived direction of sound to be pulled in the direction of a visible target (over 30 deg of separation) Multiple targets: vision improve auditory distance accuracy and lower judgment of variability under other conditions Coincidence: virtual sound sources placed at .25m and visual targets placed at larger distances (1.5m), results indicated biased judging the position of the auditory target based on their visual distance Perceptual organization: Specific distance tendency, tendency to estimate a �default� distance when distance cues were removed and provided Compress far distances and expand close distances partially related to auditory horizon, just as in vision, tendency to mark an upper limit on perceived distance. Listener�s Familiarity: estimate of sound source distance better for familiar sounds signals than for unfamiliar. Improvement after exposure to unfamiliar sound signals. Intensity: sound intensity decreases as distance between listener and sound source increases. Inverse-square law= 6dB intensity loss for each doubling of distance *ambiguous cue because sound source acoustic power and distance (from listener to sound source) can change Direct-to-Reverberant Energy Ratio: occurs in environments with sound reflecting surfaces the Radio of Energy reaching listener directly vs. the reverberant energy (reflected by surface) decreases if the sound source distance increases Spectrum: at farther distances, the sound absorbing properties of air modify the sound source spectrum by attenuating high frequencies Binaural differences: when listener moves his head, changes in azimuth will be range dependant. For sources that are close, a small shift cause a large change in azimuth, if the source increases distance there is less change in azimuth. Vision: Ventriloquism effect-> cause the perceived direction of sound to be pulled in the direction of a visible target (over 30 deg of separation) Multiple targets: vision improve auditory distance accuracy and lower judgment of variability under other conditions Coincidence: virtual sound sources placed at .25m and visual targets placed at larger distances (1.5m), results indicated biased judging the position of the auditory target based on their visual distance Perceptual organization: Specific distance tendency, tendency to estimate a �default� distance when distance cues were removed and provided Compress far distances and expand close distances partially related to auditory horizon, just as in vision, tendency to mark an upper limit on perceived distance. Listener�s Familiarity: estimate of sound source distance better for familiar sounds signals than for unfamiliar. Improvement after exposure to unfamiliar sound signals.

28. 28 Estimates of perceived distance How far away does the sound appear? Meters, walking towards auditory target, magnitude estimation, paired-comparison � different methods same results. Experiments of distance judgments demonstrate the existence of 2 aspects of distance perception: Estimate bias Close source distances are overestimated and far distances are often substantially underestimated. Estimate variability The majority of estimate variability is due to perceptual blur Distance estimates to visual targets are less variable and highly accurate Estimate bias: listeners couldn�t acurately estimate distance to a source of sound they could accurately determine if the acoustic power of sound source changed or not during changes in source distance. One explanations is that maybe the process of source loudness determination maybe able to compensate for distance estimate biases. Estimate bias: listeners couldn�t acurately estimate distance to a source of sound they could accurately determine if the acoustic power of sound source changed or not during changes in source distance. One explanations is that maybe the process of source loudness determination maybe able to compensate for distance estimate biases.

29. 29 Correlation between variability and biased estimation distance and acoustic factors Exception: direct-to-reverberant energy ratio (one stimulus presentation) The other acoustic factors: combination of multiple acoustic factors Multiple acoustic factors Intensity and direct-to-reverberant more reliable cues, but not others Framework that combines individual distance cues Consisted cues are �trusted� = high perceptual weight Unavailable or unreliable cues = less perceptual weight Final distance perfect = sum of estimates from individual cues Producing stable estimates of source distances under a wide range of acoustic conditions Acoustic factors: intensity, direct-to-reverberant energy ratio, spectrum and binaural cues The amount of bias appears in all of them Specific distance cue will not yield equally accurate distance estimates Intensity cue can be inaccurate when variation in the acoustic power of the source is present. Direct-to-reverberant can be affected by background noise Estimates can be improved with multiple trials at difference sound distances because allow to relative comparisons. Exception: the Direct-to-reverberant is relatively accurate on one stimulus presentation. Acoustic factors: intensity, direct-to-reverberant energy ratio, spectrum and binaural cues The amount of bias appears in all of them Specific distance cue will not yield equally accurate distance estimates Intensity cue can be inaccurate when variation in the acoustic power of the source is present. Direct-to-reverberant can be affected by background noise Estimates can be improved with multiple trials at difference sound distances because allow to relative comparisons. Exception: the Direct-to-reverberant is relatively accurate on one stimulus presentation.

30. 30 Distance localization performance is not degraded through the use of non-individualized HRTF�s Surprising given the known performance-degrading effects on non-individualized HRTF�s on directional localization. Implications for auditory display Spatial auditory displays should provide consistent changes in intensity and direct-to-reverberant cues (not only just one cue) just as real environments. Realistic simulation of distance does not require that the display be tailored to acoustics of individual users� head and ears (not necessary individualized HRTF). Non-individualized HRTFs can have a negatively impact on directional localization accuracy

31. 31 Incorporate a visual component since vision facilitates distance perception Use of familiar sound source signals Level of accuracy should be comparable to real-world situation (developers shouldn�t be overly optimistic in terms of perceived distance accuracy)

32. 32 - 4/4 - The Impact of Signal Bandwidth on Auditory Localization: Implications for the Design of Three-Dimensional Audio Display By Robert B. King, Simon R. Oldfield >what are the effects of limited signals bandwidth on sound localization in military 3D displays where most military aircraft have communication systems that are band-limited in frequency response.

33. 33 Researchers seeking to implement synthesized 3D audio displays (in military environment) are investigating a number of design issues: 1. Whether digital filters based on one generalized HRTFs will allow accurate spatial synthesis for all individuals 2. Intelligibility and localizability of speech signals in 3D auditory displays 3. Masking and release masking effects associated with spatially encoded displays 4. Effects on limited stimulus bandwidth on spatial synthesis

34. 34 HRTF�s: Preserve pattern of differences in time, and intensity cues that occur between ears. Preserve spectral modifications on the incident waveform by head, torso, pinnae before it reaches the basilar membrane Spectral features occurred frequencies 4kHz � 16 kHz Captures these differences and spectral modifications = code auditory signal�s position in space

35. 35 Military aircraft have communication systems that are band-limited in frequency response Low pass filters, pass frequencies of up to 4 to 6 kHz Signal�s elevation and position (front/back) are coded by frequency between 4 � 16 kHz Band limiting a signal could affect accuracy with which listeners can localize the elevation or position of this signal.

36. 36 Method Low-pass filtering with progressive removal of the high frequency content of signal High-pass � removal of low frequency� 3 subjects were presented with signal progressively low-pass filtered from low-pass 16 to low-pass 1kHz and progressively high-pass filtered from high-pass 14kHz to 1 kHz high-pass 9 elevations and 4 azimuths Speaker situated in front and behind the participant Low-pass filtering with progressive removal of the high frequency content of signal to identify the upper limits of the frequency components of the signal that are critical for its accurate localization of elevation and position (front/back) Low-pass filtering with progressive removal of the high frequency content of signal to identify the upper limits of the frequency components of the signal that are critical for its accurate localization of elevation and position (front/back)