Predicting Sound Attention and Identification

Predicting Sound Attention and Identification: Modeling Identification of Category, Subcategory, and Specific Source as a Function of Mission Context

by Angelique A. Scharine

ARL-MR-730

December 2009

Distribution authorized to U.S. Government agencies and their contractors; administrative or operational use (December 2009). Other requests for this document shall be referred to Director, U.S. Army Research Laboratory, ATTN: RDRLHRS-D, Aberdeen Proving Ground, MD 21005-5425.

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Army Research Laboratory Aberdeen Proving Ground, MD 21005-5425

ARL-MR-730

December 2009

Predicting Sound Attention and Identification: Modeling Identification of Category, Subcategory, and Specific Source as a Function of Mission Context

Angelique A. Scharine Human Research and Engineering Directorate, ARL

Distribution authorized to U.S. Government agencies and their contractors; administrative or operational use (December 2009). Other requests for this document shall be referred to Director, U.S. Army Research Laboratory, ATTN: RDRLHRS-D, Aberdeen Proving Ground, MD 21005-5425.

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Predicting Sound Attention and Identification: Modeling Identification of Category, Subcategory, and Specific Source as a Function of Mission Context

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14. ABSTRACT

Auditory situation awareness has been defined as the ability to detect, localize, and recognize relevant sound information in one’s environment. Currently, the U.S. Army Natick Soldier Research, Development, and Engineering Center and the U.S. Army Materiel Systems Analysis Activity are working on the implementation of the Auditory Detection Model that will provide the detection component of auditory situation awareness to the Infantry Warrior Simulation (IWARS) model. However, Soldiers detect many sounds that they do not attend to or recognize. This memorandum report details preparation for a project in which sound recognition and importance data will be collected to supply the IWARS model with an estimate of the probability that sound information from a particular sound event will be attended to and utilized. This is an ongoing project; therefore, this document contains all research materials collected for this project and lists all elements of the project that will be required prior to data collection. 15. SUBJECT TERMS

sound identification, IWARS, auditory situation awareness, sound recognition, attention, Soldier performance model 17. LIMITATION OF ABSTRACT

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Contents

List of Figures

v

List of Tables

v

1.

1

2.

Background and Mission Need 1.1

A Gap in the Model .........................................................................................................1

1.2

A Complex Process .........................................................................................................1

1.3

Objective .........................................................................................................................1

Organizational Overview

2

2.1

ARL-HRED Visual and Auditory Processes Branch (VAPB) ........................................2

2.2

NSRDEC .........................................................................................................................2

2.3

IWARS ............................................................................................................................2

2.4 TPA Relationships Between VAPB and NSRDEC’s Personal Protective Equipment (PPE) Program ..........................................................................................................................3 2.5 TPA Work on Complex Acoustic Environments Like Those in Urban Operations (UO) .......................................................................................................................3 3.

4.

Research Question and Variables

3

3.1

Research Question ...........................................................................................................3

3.2

Factors Affecting Attention .............................................................................................4

3.3

Factors Affecting Recognition ........................................................................................4

3.4

Levels of Identification ...................................................................................................5

3.5

Context as a Factor Affecting Level of Identification Precision .....................................5

Method

6

4.1

Experimental Tasks .........................................................................................................6 4.1.1 Task 1 ..................................................................................................................6 4.1.2 Task 2 ..................................................................................................................6

4.2

Participants ......................................................................................................................6

4.3

Materials ..........................................................................................................................6 4.3.1 Taxonomy of Military Sounds ............................................................................6

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4.3.2 Sound Recordings................................................................................................7 4.3.3 Surveys ................................................................................................................7 4.3.4 Mission Vignettes ................................................................................................8 4.3.5 Varying SNR .......................................................................................................8 4.3.6 Distance ...............................................................................................................9 4.3.7 Impulse Response Measurements to Create Acoustic Conditions: Reverberation and Indirect Sound Pathways...................................................................9 4.4

5.

Tests and Potential Tests ...............................................................................................10 4.4.1 Sound Importance Ratings ................................................................................10 4.4.2 Sound Identification as a Function of SNR .......................................................11 4.4.3 Sound Identification as a Function of SNR for Non-Steady-State Noise .........11 4.4.4 Signal Detection ................................................................................................12

Issues and Limitations 5.1

12

Experimental Design Issues ..........................................................................................12 5.1.1 Set of Target Sounds .........................................................................................12 5.1.2 Informational Masking ......................................................................................13 5.1.3 Recordings .........................................................................................................13 5.1.4 Maintaining Relevance to the Soldier ...............................................................13

6.

Conclusion

14

7.

References

15

Appendix A. Taxonomy of Military Sounds: Vehicle, Weapon, and Aircraft

17

Appendix B. Sound Files Currently Available

31

Appendix C. Concatenated Survey Responses: Sounds Encountered by Foot Patrol or During Reconnaissance

39

Distribution List

45

iv

List of Figures Figure 1. Layout of manikins and sound sources used to make impulse noise recordings. .........10 Figure 2. Manikins and shock tube (photo taken 9 February 2009). ............................................11

List of Tables Table 1. Questions used in the survey of SMEs on relevant sounds heard during urban operations. ..................................................................................................................................8

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INTENTIONALLY LEFT BLANK.

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1. Background and Mission Need 1.1

A Gap in the Model

The Technology Program Agreement (TPA) “Auditory Capabilities in an Urban Terrain – Situational Awareness” (ACUTE-SA) NA-HR-2007-02 between the U.S. Army Research Laboratory’s Human Research and Engineering Directorate (ARL-HRED) and Natick Soldier Research, Development, and Engineering Center (NSRDEC) had as its objective to conduct research on Soldier auditory capabilities as a function of their acoustic environment and equipment. Specifically, the goal was to quantify the effect of the acoustical environment on dismounted Soldier performance on mission tasks, such as street patrols, building clearing, and reconnaissance. Recently, the Auditory Detection Model (ADM) was implemented as a part of the Infantry Warrior Simulation (IWARS) model. This represents an important upgrade to the IWARS model, as hearing is often the first source of information about events in the surrounding environment and serves as an important sensor for the Soldier. However, detection is only the first step in complete auditory situation awareness (SA). Typically, we define auditory SA as detection, recognition, and localization. In thinking about how such information could be added to the IWARS model, it became clear that should the IWARS team attempt to incorporate recognition and localization into their auditory sensation module, no data exist in a format that could be used to inform the model. Localization data will be collected when the ARL Environment for Auditory Research facility is completed. This work is covered under a new, near-term TPA “Auditory Data Development in Support of IWARS” (NA-HR-2010-01) to commence in October 2010. 1.2

A Complex Process

Sound recognition is a complex process, affected by numerous factors and achieved in a number of ways. Accuracy is affected not only by physical features, such as reverberation, the physical pathway, noise and atmosphere, but by cognitive factors that vary by mission needs and personal characteristics. Furthermore, it is important to consider the level of recognition and identification required by the particular context. Rather than collect a small set of data that cannot be generalized beyond a limited set of circumstances, we chose to focus on developing a larger set of test materials while working with subject matter experts (SMEs) in order to develop experimental conditions that reflect a close match to the context in which dismounted mission tasks are carried out. 1.3

Objective

This report will detail the current state of work on this project, report on the materials gathered, and summarize the plans as they currently stand at this stage of development.

1

2. Organizational Overview 2.1

ARL-HRED Visual and Auditory Processes Branch (VAPB)

ARL-HRED traditionally conducts research and analysis on matters that affect the infantry Soldier – the ground Warrior. As such, it is understood the human must interact with equipment and the research is centered on the related human factors issues. Much of this research deals with Soldier’s interaction with specific equipment under development and is therefore classified as 6.2 research. However, the Auditory Research Team of VAPB conducts primarily basic, 6.1 research into issues of auditory perception as they relate to the Soldier. Typical research topics include research into auditory localization, speech communication, bone conduction transmission, and hearing protection. 2.2

NSRDEC

The mandate of NSRDEC is to ensure that Soldiers are well fed, protected, and equipped through materiel solutions. NSRDEC is the organization responsible for the development of the MRE (meals ready to eat), Soldier uniforms, and protective gear. The Warfighter Science, Technology, and Applied Research Directorate serves as the lead organization for planning and executing the research and development of protective clothing and individual equipment for the Warfighter. As such, it conducts basic and applied research to support program and product managers. 2.3

IWARS

IWARS is PC-based software designed to assess the combat worthiness of systems and subsystems for individual dismounted Warfighters and small dismounted units during urban operations. IWARS is being codeveloped by NSRDEC and the U.S. Army Materiel Systems Analysis Activity. IWARS allows the input of details regarding force structure, equipment, threats, and individual performance characteristics. These details can be used to simulate performance in a specific scenario vignette. It has been validated for use in the Analysis of Alternatives of materiel development program and is intended for assessing the impacts of Command, Control, Communications, Computers, Intelligence, Surveillance, and Reconnaissance technologies on lethality, survivability, and mobility. In the previously released version 1, it had implemented a visual target detection module. Auditory sensory capabilities in the form of ADM and rough localization are being implemented as part of a new release.

2

2.4

TPA Relationships Between VAPB and NSRDEC’s Personal Protective Equipment (PPE) Program

Initially, an HRED – NSRDEC TPA supported the PPE program and its development of helmets and other personal protective headgear by providing data related to the effects of headgear on auditory performance. For example, VAPB contributed to NSRDEC’s development of the advanced combat helmet by providing research showing improvement in localization performance for those wearing it vs. those wearing the previous helmet from the personal armor system for ground troops (PASGT). This improvement has been shown to be due to the reduced ear coverage as compared to the PASGT helmet. Further, the effects of ear coverage have been shown to increase in environments with normal, nonlaboratory acoustics. A model has been created and is being developed to predict these effects in order to assist with future helmet design. VAPB has also supported programs at NSRDEC by testing prototype designs and consulting on communications and hearing protection issues. 2.5

TPA Work on Complex Acoustic Environments Like Those in Urban Operations (UO)

More recently, the research focus has shifted to the effects of complex acoustic environments (like those present during UO) on Soldier auditory performance. These are summarized in a technical report (Scharine and Letowski, 2005) and recent journal article (Scharine et al., 2009). This research fills a gap in traditional auditory research and highlights the complexity of the auditory environment and its interaction with personal equipment. However, basic research data does not directly tie degraded auditory performance to performance on dismounted Soldier mission tasks. It can only suggest that performance will be hindered. Providing data for the IWARS model will tie differences in acoustic conditions due to the environment and Soldier equipment directly to mission performance. This will increase the accuracy of predictions made by the IWARS model. It also ties together the strengths of ARL and NSRDEC, allowing NSRDEC to relate the effects of their equipment designs directly to performance in the field.

3. Research Question and Variables 3.1

Research Question

The ADM disregards the fact that numerous sounds are detectable in a given environment and receive varying levels of attention from the Soldier. Humans learn to filter sensory information, attending only to that which is relevant for their current situation. Thus, the overriding research question is, “Will the Soldier recognize and attend to a sound event?” Determining this is problematic because, to some degree, a sound will not be recognized unless it is attended to; yet, it will not be attended to unless some degree of preliminary processing determines that it is a sound of interest. For the purposes of modeling, we will assume that the answer lies in an 3

interaction between the importance of the sound within a given mission context and the general recognizability of that sound. Recognition is affected by a number of factors, some of them physical (detectability, degradation by the environment) and others attentional. Further, recognition can occur on a number of levels, from very general (e.g., that was an explosion) to very specific (e.g., that was an AK47). Therefore, we need to know whether the sound is important in a given context and the value of each level of recognition, from general to precise. Then, in a given acoustical environment, we need to know whether enough physical information is present for the sound to be recognized and what level of recognition is possible. 3.2

Factors Affecting Attention

For the purposes of modeling, we will define attention as overt attention, e.g., the act of directing the senses (vision, hearing, smell, etc.) toward a stimulus source to gather information. Attention can be affected by situational factors such as the task at hand, workload, and physical environment. However, it can also be affected by individual factors—temperament, fatigue, or mindset. It is not feasible to measure or model all of these factors, but it is reasonable to assume that some sounds will be more important in one context vs. another. Further, the level of detail attended to will also differ with the context. It must be assumed that the other factors will only serve to increase the variance in any estimate of attention until they are explicitly modeled. 3.3

Factors Affecting Recognition

Sounds are identified in a number of ways. On the face of it, identification appears to be a template-matching or pattern-recognition process (Reed, 1992). However, like any form of identification, this is an oversimplification of the task. First, no two sound events by the same source are identical. Rather than identifying a sound based on a specific profile, a listener is listening for a critical feature, e.g., timbre, rhythmic pattern, or a conjunction of both (Gibson, 1969). Second, sound is changed as it travels through space, is reflected from surfaces, and is absorbed by the surfaces and the atmosphere (Wiener, 1960). Thus, the sound may be quite different depending on where the listener is positioned in relation to the sound event. Changes in the atmosphere can severely attenuate sounds otherwise audible in a particular location. Finally, other sound events presented concurrently may mask and obscure the sound. A sound is usually recognizable if it is at least a few decibels above the hearing threshold (Allen, 1994; Andringa and Pals, 2009). However, the salient feature that usually signals a particular sound event or distinguishes it from another may not be detectable. Thus, the features used to identify a sound depend on the sound itself, other sounds in the set of sounds to be distinguished, and auditory context. A listener will usually use the features most likely to be informative (Dash and Liu, 1997) based on his or her prior knowledge. The specific features used will change as a function of the context and individual experience of the listener.

4

3.4

Levels of Identification

Gibson (1969) describes the levels of perception as detection, discrimination, recognition, and identification. We can expand on this, saying that identification is hierarchical: one can identify a sound event as coming from a general category of sources, a subset of that category, or a specific exemplar. For example, weapon fire can be identified as an explosive event, gunfire, or as an AK47. The similarity of items within a set or across sets will affect the degree to which sounds are misidentified. For example, a tracked vehicle will be easy to distinguish from a wheeled vehicle. Distinguishing an Abrams from a T-72 tank may be more difficult. Items within one category of sounds may be more confusable than items within another, and this confusability may vary across sets as well. For example, helicopters can sometimes be identified acoustically from the frequency relationship between the main and tail rotor or the dual rotors. Because the mechanical aspects are fixed, there is a consistent cue that can be used for identification and some, but not all, helicopters can be identified reliably. On the other hand, small arms weapon fire may be more difficult to identify. The mechanical differences and size of the ammunition make consistent differences in the resulting sound. However, these differences are small compared to the variability between successive shots due to changes in the surrounding environment, direction of fire, and listener position relative to the sound. Because items from a set containing many very similar items will be harder to identify than one having very diverse items, it is important to confer carefully with SMEs to ensure that the “soundscape” of this study reflects that of the military environment. 3.5

Context as a Factor Affecting Level of Identification Precision

The level of precision of identification required depends on how much information is needed to respond appropriately. At times, a lower level of identification will be sufficient, allowing the Soldier to take evasive action. If he is on patrol, it is likely that any explosive sound will be attended to, regardless of the level of identification. However, higher levels of identification may increase the Soldier’s SA, allowing him to gain additional information, predict future threats, and plan ahead. The level of identification needed and the ability to identify a sound will depend on other contextual factors such as the probability of certain events occurring in the current environment, knowledge about one’s own resources and those of the oppositional forces, and the need to respond or use the information about the sound event. Thus, a measure of importance will be recorded for each level of identification. This will provide a qualitative measure of the functional importance of identification precision in each context.

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4. Method 4.1

Experimental Tasks

4.1.1 Task 1 SMEs rate military sound importance as a function of mission vignettes. SMEs will identify how useful each level of identification precision is in terms of SA. Levels of identification are provisionally defined as general category, category subset, and specific exemplar. 4.1.2 Task 2 SMEs identify a random subset of military sounds as a function of distance, signal-to-noise ratio (SNR), and acoustic conditions. SMEs will be trained on the different levels of classification, familiarized with the kinds of categories and subcategories of sounds present in the experiment, and instructed to identify at the highest level of precision possible. 4.2

Participants

SMEs in this case are infantry Soldiers or Marines. Preference will be given specifically to those who are veterans of deployments to Iraqi urban areas. A minimum of 12 participants will be needed for each task. As it is unlikely that the tasks will be run concurrently, it is also unlikely that any one Soldier will complete both tasks; however, it is not prohibited. Attempts will be made to ensure that the participants completing task 2 meet H1 hearing criteria as defined by U.S. Army Regulation (AR) 40-501 (2005), with an average threshold level at 500, 1000, and 2000 Hz that does not exceed 25-dB hearing level (HL) and with no individual threshold greater than 30-dB HL; and that the threshold at 4000 Hz is not greater than 45-dB HL. However, any deviation from these criteria will be documented and the data from that participant will be analyzed separately. The investigators will adhere to the policies for protection of human subjects as prescribed in AR 70-25 (1990). 4.3

Materials

4.3.1 Taxonomy of Military Sounds Appendix A lists sounds from three categories—vehicle, weapon, and aircraft for the United States and for Iraq. Whenever possible, sounds from vehicles and weapons used by Iraqi insurgents are listed as an example of sounds produced by the oppositional forces. However, one of the difficulties for Soldiers, and for the design of this study, is the Iraqi military is not the enemy and the insurgents use whatever weapons or vehicles they can obtain or make. Therefore, their weapons can be the same as the American or Iraqi forces, and their vehicles are 6

usually civilian cars and trucks. This makes them difficult to distinguish. Thus, the items included in the list represent a partial set, including only some of the military vehicles and weapons reported to be commonly used by insurgents. 4.3.2 Sound Recordings Initial recordings of sounds need to be high fidelity, at least 44.1 kHz, with 16-bit quantization sampling rate. Because the experiment measures specific ability to identify sounds, the sources of recordings must be known (i.e., no “Foley”-type sound effects). They should be free of reverberation, except in the case of weapon fire, where they should be free of perceptible reverberation. Ideally, there should be several examples of the same sound. Given that the amount of time required for gaining access to the sound sources and setting up equipment is large in comparison to the difficulty of making recordings with that setup, recordings of multiple events and conditions (distances and angles) are being made at every opportunity. In other cases, recordings are being obtained from reliable sources, such as the U.S. Army Aberdeen Test Center (ATC). In this case, permission was obtained from the program managers and the recordings are treated as For Official Use Only information. Appendix B lists the current recordings, with details about their sources. 4.3.3 Surveys An informal survey was circulated to gather information about sounds encountered during patrols or reconnaissance activities. Table 1 shows the survey questions used. Survey responses were collected from a medic, a Bradley Fighting Vehicle (M2) commander, an infantry captain, and five Soldiers with the infantry military occupational specialty (MOS) of 11B, including three Sergeants First Class. Some of the surveys were completed via email, others via telephone. Appendix C shows the responses that were compiled. The goal at that time was to collect information about the “soundscape” in order to choose “foils,” sounds that would be present in the context of urban operations, but would not be target sounds. At that time, the plan was to collect data in the form of a signal detection task, and these sounds were needed as “false alarms.” The survey responses indicated that very few sounds are confused with weapon fire or explosions, and the difficulties lie in the informational masking * that occurs due to distracting sounds in the environment. Consequently, the signal detection paradigm may be useful only for a limited set of sounds, such as those encountered in the ambient environment. It will be necessary to combine the signal detection paradigm with other methods in order to obtain meaningful data about sound recognition. Continued input from SMEs will used to select the sound set for the signal detection paradigm and for refinement of the full list of sounds and other experimental methods.

*Informational masking is a term that refers to decreased detection of target sounds that is not due to energetic masking. It is

a term that can describe failure to attend to a sound that is technically audible because of distraction.

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Table 1. Questions used in the survey of SMEs on relevant sounds heard during urban operations. 1.

What sounds get mistaken for weapon fire, explosions, or reloading a weapon?

2.

Can vehicles be identified on the basis of sound alone? What do you listen for? Are there distinctions of interest between U.S. and Iraqi vehicles?

3.

Are there distinctive characteristics to UAVs or MAVs that make them stand out soundwise, or are you just listening for a sound coming from above?

4.

Are footsteps a source of information? If so, what do you listen for?

5.

What other sounds are “just there?” What sounds get in the way of hearing important sounds?

Notes: UAV = unmanned aerial vehicle, and MAV = manned aerial vehicle.

4.3.4 Mission Vignettes The importance of a sound depends on the situation in which it occurs. Hearing speech inside of a building depends on who is talking, who is listening, and what the listener is trying to accomplish. To provide a context for ratings representative of the type of environment being modeled in IWARS, mission vignettes will be used. Fred Dupont, the NSRDEC representative to Fort Benning’s Maneuver Center of Excellence and the U.S. Army Infantry School, was contacted for assistance because similar sorts of scenarios are used for testing activities at the McKenna Military Operations in Urban Terrain site at Fort Benning, GA. As a result, a set of vignettes is being obtained from the U.S. Army Training and Doctrine Command (TRADOC) and being developed for use by NSRDEC. They are not currently complete, but the goal is to have a set of vignettes that have been approved by TRADOC for use in the measurement of equipment effects on Soldier performance. We hope to use these same vignettes to quantify sound importance as a function of context. 4.3.5 Varying SNR Raising the noise level raises the sound detection threshold level. By varying the level of noise with respect to the target sound, we can quantify the SNR level required for identification and how this changes as a function of acoustic condition. However, another feature is the effect of random sounds that are variable in level and content. A Soldier commented that it was not so much that a sound was confused, but that there were too many things to listen to. For example, a Soldier reported that a decoy would be planted by insurgents to try to draw attention away from insurgent activities. This kind of unpredictable ambient noise is probably the most relevant in terms of describing threats to auditory SA. It is also the most difficult to measure experimentally. Steady-state noise primarily causes energetic masking, but time-varying noise causes both energetic and informational masking. To measure its effects, very short (