Auditory Displays

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Theme of Research Articles. Auditory displays provide benefits over visual displaysCare should be taken in design of auditory warnings to combine qualities of acoustic urgency and situational urgency3 D audio can be effectively implemented with server based COTS items but will require operator visual feedback training to compensate for lack of individualized HRTFsAuditory Icons can be employedMilitary and Industrial workers should carefully weigh the protective benefits of HPDs with helmet w9444

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Auditory Displays

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1. Auditory Displays Vause & Grantham (1999) Wang et al (2002) Haas & Casali (1995) Burt et al (1995) Belz et al (1999)

2. Theme of Research Articles Auditory displays provide benefits over visual displays Care should be taken in design of auditory warnings to combine qualities of acoustic urgency and situational urgency 3 D audio can be effectively implemented with server based COTS items but will require operator visual feedback training to compensate for lack of individualized HRTFs Auditory Icons can be employed Military and Industrial workers should carefully weigh the protective benefits of HPDs with helmet wear against the loss of localization capabilities and the likelihood/danger of front/back errors

3. Vause & Grantham (1999) Background Sound localization critical to survival Essential to orientation/surveillance of environment Critical in military and industrial settings Helmets worn to protect head from injury Hearing Protective Devices (HPDs) worn to protect from hearing damage Previous Studies Early military helmet designs (Hayes-Stewart and M-1) did not disrupt localization performance; Randall & Holland (1972) Increased localization errors found when tanker helmets worn with HPDs; Howse & Elfer (1982) HPDs wear resulted in significant localization difficulties; Abel & Hay (1996), Atherly & Noble (1970), Noble et al (1990) and Noble & Russell (1972) Not known if helmet design (amount of ear pinnae occlusion), overall attenuation or frequency-specific characteristics of HPDs were factors in above results

4. Vause & Grantham (1999) Purpose of Study What is the effect of wearing Kevlar helmet with no or one of two types of earplugs on sound localization ability? - Can any sound degradation be accounted for simply by the attenuation provided? What were the combined effects of the Kevlar helmet and earplugs on horizontal plane localization performance - Does HPD affect performance for a person wearing a helmet

5. Vause & Grantham (1999) Participants 6 adults with normal bilateral hearing 5 active duty, Reserve, or ROTC cadet 1 university student Methods Subject seated in center of anechoic chamber Surrounded from – 80 to + 80 degree hemifield of 43 speakers with 4 deg arc separation

6. Vause & Grantham (1999) Methods 8 experimental conditions BH = bare head/open ears EAR = bare head/EAR ear plugs ER25 = bare head/ER25 plugs K = Kevlar helmet only K+EAR = Kevlar with EAR plugs K+ER25 = Kevlar with ER25 plugs BL = bare head/open ears at lower SPL of 35 dB BH2 = 2nd bare head/open ears DV: Sound localization performance IVs: protection condition and orientation to sound (front/lateral)

7. Vause & Grantham (1999) Methods Stimulus: digital recording of cocking of M-16 rifle at 60 dB for all except barehead at 35 dB Participant facing front to center of speaker array or lateral with center of speaker array at left ear Stimulus emitted in random from one of 20 speakers, 4 x per speaker 3 runs per orientation, 6 runs per earplug/helmet condition Called out speaker # and was allowed to visually locate

8. Vause & Grantham (1999) Results K = no sig diff to BH; no sig diff in front/back confusions EAR =large sig diff in lateral ER25= sig diff in both frontal and lateral to BH; sig diff in lateral to BL K+EAR = sig diff in lateral; large increase in front/back confusions K+ER25 = small but sig in frontal compared to K; sig diff in lateral; large increase in front/back confusions

9. Vause & Grantham (1999) Conclusions Kevlar helmet by itself doesn’t significantly affect sound localization performance compared to no helmet Earplugs by themselves decreased sound localization performance in the frontal orientation but was only significant for ER25 In the lateral orientation, both types of earplugs decreased performance significantly Moreso for the EAR – presumably due to disruption of spectral cues caused by differential attenuation Data couldn’t answer conclusively whether the ER25 lateral disruption was accounted for by the flat attenuation Combining earplugs with a Kevlar helmet substantially increased localization errors in the lateral orientation through large increases in front/back confusions Small but not significant decrease in lateral orientation errors found in second bare head/open ears condition

10. Vause & Grantham (1999) Further research needed Look at effect of long-term wear of HPDs with head protection and reduction of location errors Development and use of protective devices that offer both adequate hearing protection without sacrificing localization ability In the meantime, military and industrial workers may have to choose between hearing protection and localization performance

11. Wang et al (2002) Purpose: To address limitations in use of Commercial off-the-shelf (COTS) 3 D sound cards in 3D auditory displays Development of a client/server systems utilizing COTS 3D sound cards Utilizing a method of visual-feedback training for 3D sound localization

12. Wang et al (2002) Background/Problem Set 3D audio beneficial for Spatial Localization outside of user’s field of view Reduce visual display clutter and cue interpretation time Differentiate multiple concurrent sound sources Custom-built 3 D audio systems tuned to listener and sound position and orientation (Head Related Transfer Functions, HRTF) are prohibitive due to time and cost

13. Wang et al (2002) Solution offered by COTS 3D sound cards Limitations: Platform limited (Windows/Intel PC only) Resource limited No standardized application programming interface (API) that supports all features Vendor instability Lack of support for individualized HRTFs

14. Wang et al (2002) Rockwell Scientific Company (RSC) 3D audio server Integrates 3D audio into applications through TCP/IP Supports pre-generated or live sound sources through line input or streamed over IP Utilizes a common API between the client and server independent of the 3D audio system Eliminates need to program in multiple APIs Support added for new APIs without client code changes Computing resources not limited to user’s PC

15. Wang et al (2002) Proposal: Method of visual feedback training to help compensate for lack of individualized HRTFs Without HRTFs, sound source localization accuracy is often degraded Listeners are provided with paired auditory and visual feedback to sound source location May help perceptually re-map to modified spatial cues

16. Wang et al (2002) Subjects wore Head Mounted Diplay with 6 dof head tracker Presented sound source via headphones using a COTS 3D audio card via the 3D audio server 144 spatial positions tested, 18 each from 8 spatial regions Pre-test, training phase, post-test (4 days after training)

17. Wang et al (2002) Pre-test: recorded subject’s ability to judge position of sound source with generalized HRTF; no feedback provided Training: same as pre-test but with visual feedback to subject who corrected via cross-hair on HMD Post-test: same as pre-test but 4 days post training

18. Wang et al (2002) Results Largest improvements in accuracy were seen in a reduction in front-back confusions Improvements lasted at least several days Conclusions COTS 3D audio use with server can open up opportunity for low cost availability User’s can be trained via visual feedback to compensate for lack of individualized and costly HRTFs

19. Haas & Casali (1995) Background Auditory warning signals can improve operator performance and reduce accidents Problems Mismatch between perceived and situational urgency Masking background noise Signal annoyance Other task-driven attentional demands Signal characteristics can improve urgency rating Lack of research on specific signal parameters on both subjective and objective performance

20. Haas & Casali (1995) Purpose To investigate effect of pulse format, pulse level, and interpulse interval on the perceived urgency of warning signals To investigate the effect of these variables on the response time to warning signals Examine the relationship between perceived urgency and response time tow warning signals

21. Haas & Casali (1995) Method 36 subjects (18 male, 18 female) with unimpaired hearing in 500 – 3000 Hz range Subject sat in center of diffuse sound field facing away from loudspeaker DV: 1) magnitude estimation of signal urgency 2) response time in ms to warning signals 3) paired comparison ranking of signal urgency

22. Haas & Casali (1995) IVs: 1. Pulse Format Simultaneous – 500, 1K, 2K, 3K Hz Sequential – 500, 1K, 2K, 3K Hz Sawtooth frequency-modulated: 500 to 3K 2. Interpulse interval 0 ms 150 ms 300 ms 3. Pulse level 65 dB 79 dB

23. Haas & Casali (1995) Procedure Each participant underwent 4 sessions Audiogram Magnitude estimation (perceived urgency rating) Response time and probability monitoring task Paired comparison task Signals presented over 68 dB masking noise

24. Haas & Casali (1995) As length of interpulse interval increases, perceived urgency decreases As pulse level increases, perceived urgency increases As pulse level increases, pulse interval perceived urgency increases Sequential pulse rated less urgent in all conditions Sawtooth pulse more urgent under all conditions 0ms interval rated more urgent at both pulse levels

25. Haas & Casali (1995) Paired Comparion Data: Pulse Format x Pulse Level Interaction Perceived urgency increases as pulse level increases Sawtooth and Simultaneous formats rated significantly more urgent than sequential at both pulse levels Sequential rated significantly less urgent

26. Haas & Casali (1995) Response Times Results Pulse format and pulse level were significant factors in response time Response time was longer with sequential pure tones than with sawtooth and simultaneous No difference between sawtooth and simultaneous Decreased response times at high pulse levels

27. Haas & Casali (1995) Higher pulse levels elicit higher perceived urgency and decreased response times Signals with shorter interpulse intervals elicited higher perceived urgency but did not significantly decrease response times Both sawtooth frequency-modulated and simultaneous pulse formats elicited both higher perceived urgency as well as better response times

28. Haas & Casali (1995) Conclusion Future experiments should tease out how much of an increase in pulse is ideal (too much or too little) given background noise and attentional load Should look at even longer interpulse intervals that would allow speech commands/warnings in between Should look at the relationship between perceived and situational urgency to response rates

29. Burt et al (1995) Background Cockpit caution and warning signals designed to attract pilot attention/provide information about current or impending hazards Auditory warnings can have nuisance characteristics that make them less effective Most significantly is they lack a sense of situational priority particularly when elicited among other warnings

30. Burt et al (1995) 4 Hypotheses Subjects will be able to rank the perceived urgency of warnings Faster reaction times will occur during a manual tracking task and in response to the most urgent warning (perceived) EEG alpha and theta will increase during automated tracking and that an increase in alpha and theta will be seen in interaction of automated tracking to least urgent warning An increase in attentional engagement will be seen in an EEG and Event Related Potential (ERP) in response to the most urgent warning (perceived)

31. Burt et al (1995) Method: Subjects wore elastic electrode head cap for EEG and ERP Session 1: rated urgency of warnings from least urgent to most urgent Session 2: rated urgency of warnings from zero (not urgent) to 100 (very urgent) Session 3: tracking and reaction time task with warning associated with system failure probability Tracking was either automatic or manual Session 4: rated urgency of warnings but instructed to ignore meanings given to warnings during tracking session

32. Burt et al (1995) Results – Subjective Assessments Ratings of urgency level Significant difference between high and moderate urgency warnings and high and low urgency warnings Ranking of urgency level Subject rankings were in agreement with perceived urgency scales Post ratings changed

33. Burt et al (1995) Results – Response Times Reaction times were significantly faster in response to both perceived and situational urgency during the automated tracking task compared to manual. Results – EEG and ERP Automated tracking saw increase in alpha and in low and moderate perceived urgency signals Highest alpha in low siutational urgency and manual tracking Most alert response (beta) to high situational urgency during automated tracking Largest early ERP amplitude seen in response to moderal urgency warning Larget later ERP amplitude seen in response to high urgency warning during manual tracking and in low urgency during automated tracking

34. Burt et al (1995) Conclusions – Hypothesis 1 Subjects could rank perceived urgency based only on the frequency and harmonic components of signal Rankings were altered by task that reassigned rankings randomly not based on acoustic characteristics

35. Burt et al (1995) Conclusions – Hypothesis 2 Slower tracking times seen for both peceived and situational urgencies in manual task Conclusions – Hypothesis 3 Increased alpha EEG recording in automated tracking for both perceived and situational urgency signals Only situational urgency independent of tracking condition produced differences in alpha

36. Burt et al (1995) Conclusions – Hypothesis 4 Significant urgency level effects were found for EEG and ERP in the situational urgency manipulation while only a single interaction effect was found in the perceived urgency Situational manipulation of urgency produced significantly different physiological responses to the warnings

37. Burt et al (1995) Discussion In operational settings, sense of urgency of an auditory warning will be based upon its inherent acoustic properties and its situational context EEG and ERP are sensitive measures along both dimensions but moreso for situational urgency manipulations Need to investigate auditory warnings with a larger range of sound parameters Examine the value of direct urgency mapping – compare group with correct mapping to group with inverse urgency mapping Use knowledge gained to design auditory warnings that promote optimal states of attention and awareness

38. Belz et al (1999) Looked at using auditory icons as effective warning signals Representational sounds that have specific stereotypical meanings defined by the objects or actions that created the sound Used impending front-to-rear and side collisions in driving simulator and identification of signal meaning Used male drivers with CDLs

39. Belz et al (1999) Front-to-rear collision scenario DV was response time – initial and braking IV’s Display presentation mode No display Dash-mounted visual only Auditory icon only Conventional auditory only Mixed auditory icon and visual Mixed conventional auditory and visual Vehicle speed and headway 35 mph 55 mph 2.5 s or 3.5 s headway

40. Belz et al (1999) Side Collision Scenario DV – collision avoidance – did or didn’t IVs Dash mounted iconic display (yes or no) Mirrors (yes or no) Auditory Display (iconic or conventional) Speed (35 or 55 mph) Workload (low or high)

41. Belz et al (1999) Results Front-to-rear collision Auditory icons elicited significantly faster brake response times than conventional or no display conditions No significant difference between conventional and the no display condition Both multi-modal displays elicited faster response times than only the dash-mounted visual or the conventional audio alone No differences between auditory icon alone and multi-modal displays (with auditory icon)

42. Belz et al (1999) Results Side Collision Avoidance Significantly fewer collisions with auditory icon than conventional auditory warning Mirror used resulted in fewer collisions Significant effect of using visual display with auditory icon – reduced collisions

43. Belz et al (1999) Results Correct Identification of signal meaning Approx half of participants could recognize conventional auditory signal meaning 96% could correctly identify auditory icon meaning Display preference Front to rear = combined auditory and dash-mounted visual display Side Collison = mirrors, auditory display and dash-mounted visual

44. Belz et al (1999) Research needed on workload effects of multi-modal displays Research in more realistic environment – background noise effects, traffic congestion, time-pressure, etc Auditory icons as representational sounds show great promise for use as warning signals

45. Conclusions More research into situational and acoustical construct of warning signals needed Utilization of multi-sensory modes of warning/communication is the present Best fit should incorporate limitations imposed by hearing and head protection

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