20Q: Auditory Fitness for Duty

From the Desk of Gus Mueller

My first job as a clinical audiologist was in the Army, stationed at Brooke Army Medical Center in San Antonio.  I vividly recall each Wednesday morning at 7:30 when the bus from the downtown military induction station would arrive at our clinic.  Looking out the window, I’d see 15-20 guys get off the bus, all with one thing in common—they had failed the automated hearing screening test at the induction station.  They usually fell into three different groups of fairly equal distribution. The first group was comprised of those who enlisted in the Army, but have a hearing loss that will prevent them from serving; most of this group will be going home.  The second group were those who were drafted into the Army, but have a significant hearing loss; most of this group will be going home too.  The third group was those who were drafted into the Army, do not have a hearing loss, but are malingering one to avoid serving; most of this group will be going to Vietnam.

Gus Mueller

I had two technicians helping me, and our job simply was to determine “fitness for duty” for all these individuals, and to be finished by the time the bus came back at 4:30 to pick them up.  It was quite the day.  Tears and shouting matches were common.  If we did our job right, most of these individuals would leave our clinic unhappy.  I’d go home with the somewhat uncomfortable thought: “The summary reports that I wrote today will have a huge impact on the lives of many of these young men.”

That was over 40 years ago, but the role of the audiologist remains as critical today for determining fitness for duty.  And, it’s not just the military.  Many of you have been involved in auditory fitness evaluations for the police, firefighters, pilots, homeland security positions, and several other occupations.  Because our testing and recommendations so often impact a person’s life, we want to get it right.  Fortunately, there is a team of researchers helping us out and our guest author this month is the chief scientist from that team.

Douglas S. Brungart, PhD, is Chief Scientist for the Audiology and Speech Center at the Walter Reed National Military Medical Center in Bethesda, MD.  He holds advanced degrees in electrical engineering and computer science from the Massachusetts Institute of Technology. He has authored more than 30 peer reviewed journal articles and has been issued 11 US patents for his work in audio display technology.  His numerous awards include the Military Audiology Association Research Award in 2013.

Since 2010, Dr. Brungart also has been serving as the Chief Scientist of the DoD Hearing Center of Excellence.  For those of you not familiar with this center, it is the first organization with the specific mission of coordinating efforts for hearing research among the many laboratories and medical facilities across the DoD, with a focus on the prevention, diagnosis, mitigation, treatment and rehabilitation of hearing loss and auditory injury.  Regarding this month’s 20Q article, these coordinated collaborations are what made it possible to develop an organized auditory fitness for duty effort focused on the needs of and with buy-in from all three services (Army, Navy, Air Force).

Not all of us were productive during our high school days, but our 20Q author spent his spare time starting his DoD research career as an intern at the Air Force Research Laboratory at Wright-Patterson Air Force Base in Dayton, Ohio.  It’s to our benefit that Doug continued his interest in research and the needs of the DoD personnel, and shared some of his insights and recent research findings with us here at 20Q.

Gus Mueller, PhD 
Contributing Editor
March 2014

To browse the complete collection of 20Q with Gus Mueller CEU articles, please visit www.audiologyonline.com/20Q

20Q: Auditory Fitness for Duty

1.  Walter Reed Medical Center . . . that’s a place with a lot of audiology history, right?

Most certainly.  What started off as Walter Reed General Hospital in 1909 became Walter Reed Army Medical Center in 1951. In 2011, we merged with the National Naval Medical Center in Bethesda, Maryland, and our official name changed to the Walter Reed National Military Medical Center. 

This merger has resulted in an expanded mission and a new name, but we still take great pride in the long history of contributions Walter Reed made to the field of audiology.  Our center was originally established as the Army Audiology and Speech Center (AASC) in 1943, about the same time that Dr. Raymond Carhart was assigned to one of the other three military audiology centers, Deshon General Hospital.  And you’re right, a lot of notable audiologists have passed through the Walter Reed doors and contributed to the success of our center over the past 70 years.

Today our center, which is now called the National Military Audiology and Speech Pathology Center (NMASC), continues to be the premier institution for research and clinical care in audiology and speech pathology within the Military Health System.  We have a unique mandate to coordinate audiology programs, conduct basic, applied and translational research, and provide consultation for hearing-aid programs, aural rehabilitation and clinical audiology and speech-pathology services across the Department of Defense (DoD).  This mission is facilitated by our unique structure, which integrates a multidisciplinary research section with more than 15 full-time research personnel in a single organization that also includes some of the largest and most capable audiology and speech-language pathology clinics in the DoD.  Our center has historically been responsible for conducting clinical research focused on the unique problems associated with military audiology and speech language pathology, including the development of auditory fitness-for-duty standards for the US Army and other military services.  We are also working closely with the DoD Hearing Center of Excellence to help develop and disseminate best practices related to the prevention, diagnosis, treatment, and rehabilitation of hearing and balance injuries across the DoD. 

2. You mentioned that one of your missions is the development of auditory fitness for duty standards?  I’ve had to fill out forms for patients dealing with this, but I’m not too sure how it all works.

Typically, auditory fitness for duty is assessed for individuals in jobs that are potentially dangerous or involve the safety of others (i.e., firefighting, law enforcement, operation of an aircraft, etc.).  Military Auditory Fitness for Duty (AFFD) standards refer to the hearing thresholds and profiles that will dictate whether a Service member is able to perform his or her duties safely and effectively in the field.  One of the main missions of our auditory fitness for duty efforts is to determine what level of hearing is necessary in order for military personnel to perform the requirements of their jobs. 

3. I would guess there are a lot of Service members in the military with hearing problems?

Sadly, yes.  Tinnitus and hearing loss are the most common permanent medical disabilities among Service members and Veterans.  Despite our best efforts to improve hearing conservation in the military, recent trends suggest that the incidence of auditory injury among Service members continues to rise by approximately 15 percent a year.  According to the Center for Disease Control and Prevention, Veterans are 30 percent more likely to suffer from hearing impairment than nonveterans, and those who have served since September 11^th, 2001, are four times as likely to have hearing loss than their civilian counterparts. 

Fortunately, this epidemic of hearing-related problems for Service members and veterans has not gone unnoticed by our nation’s leadership.  In fact, the 2008 National Defense Appropriations Act directed the establishment of a Service wide Hearing Center of Excellence (HCE) with a mission to heighten military readiness and optimize quality of life through collaborative leadership and advocacy for hearing and balance initiatives.  Through our close partnership with the HCE, we have been working closely with the VA and the Services to elevate best practices and develop standard prevention, conservation and clinical care for hearing loss and auditory injury.  An important part of this effort is a multiservice effort the HCE is helping to organize to develop improved auditory fitness for duty standards for use across the DoD. 

4. How do you identify Service members who develop a hearing problem while they are on active duty?

Although some hearing injuries are the result of acute acoustic traumas, most hearing loss in the military is an invisible injury that develops slowly over the course of a Service member’s career.  Consequently, the only way to identify hearing problems in the active duty force is to conduct regular audiometric testing.  The US Military has always played a leading role in the development of the profession of audiology, including the development of some of the nation’s first comprehensive hearing conservation programs.  Service members who are routinely exposed to high levels of industrial noise have long been required to be enrolled in hearing conservation programs that have required periodic audiometric evaluations and hearing protection fittings.  However, Soldiers, Sailors, Airmen and Marines with more intermittent noise exposures, of the type that might occur due to exposure to small arms fire during dismounted patrols, for example, have not always complied with the requirement to receive auditory evaluations at regular intervals.  Although this arrangement was less than ideal, the hearing readiness problems it caused were not apparent in the relatively conflict-free period between the Vietnam War and 9/11.  However, once the US Military became engaged in the combat-intensive environment of Operation Iraqi Freedom, they began to experience a broad range of critical hearing-related problems that made it clear that additional measures were required.  This eventually led to the establishment of the Army Hearing Program in 2006 as a comprehensive, Army-wide initiative focused on improving the prevention, treatment, and rehabilitation of hearing-related problems of US Soldiers.  This program placed a new emphasis on the requirement for Soldiers to have audiograms before entering basic training, before and after each military deployment, and prior to separation from the Service.  Furthermore, Soldiers assigned to combat arms units were now required to have annual audiometric testing even when stationed at their home bases in the US or overseas.  Another big boost to hearing conservation in the military occurred in 2012, when the US Marine Corps adopted a policy that requires all active duty Marines to have an audiogram less than one year old on file at all times. 

These new hearing readiness requirements are extremely important because they have moved us away from only focusing on the occupational exposure to noise and towards looking at the bigger picture.  That is, everyone is at risk of hearing loss, and the readiness consequences are the same whether the hearing loss results from noise on-duty or off-duty.  If we don’t measure hearing loss and provide hearing protective devices as well as hearing health education frequently, we have little ability to prevent hearing loss, or to stop it in its early stages. 

5.  Sounds like the right thing to do, but it must take a great deal of effort to collect and store audiograms on several hundred thousand Marines and Soldiers every year. 

Definitely.  It wouldn’t be possible without the Defense Occupational & Environmental Health Readiness System for Hearing Conservation (DOEHRS-HC), an automated system that allows a single technician or audiologist to collect audiograms on multiple individuals in a four-man or even an eight-man booth.  This system also provides a database for tracking annual audiogram information and any hearing sensitivity changes for all military personnel.  In addition to the DOEHRS-HC system, DoD Hearing Center of Excellence is developing an expanded registry system.  This system will collate the surveillance data with other trauma registry and clinical audiometric data from DoD and VA to offer comprehensive longitudinal data analysis of individual and aggregate data related to hearing loss and auditory system injury.

6. I know that in the civilian world, people don’t always comply with requirements like obtaining an annual audiogram.  How do you identify individuals who are not keeping up with their annual testing?

Compliance is always one of the biggest issues in the development of a successful hearing conservation program.  Prior to 2006, compliance was a big problem is the Army as well.  However, this problem largely went away when one of our previous directors, Colonel Kathy Gates, was able to successfully advocate for a hearing readiness metric to be integrated into the Army Medical Protection System (MEDPROS).  This is the first element of the Army Hearing Program.  Hearing Readiness is tracked and provides Soldiers and Commanders critical information about hearing status.  A Soldier is tracked in the Army Readiness application and if their hearing data exceeds 13 months they show up "red" in MEDPROS.  This requires them to complete a hearing test in order to become "green" and ready to deploy.  As a result of this hearing tracking system, hearing readiness increased from 69 to 90% compliance within the first year. 

7. So once you have their pure tone thresholds, does that then determine their fitness for duty?

Not completely, but it provides a good starting point.  Current standards for auditory fitness for duty differ slightly, but all three Services have a similar structure for fitness-for-duty evaluations.  As an example, let’s consider the auditory fitness-for-duty system currently used by the Army, which characterizes a Service member’s hearing profile as H1, H2, or H3. 

• H1 Profile:  The H1 profile is often assumed to indicate that a Service member has “normal” hearing, but it really means that the individual has no more than a “mild” hearing loss.  In the Army, this means that the audiometer average level for each ear is no more than 25 dB at 0.5, 1, and 2 kHz with no individual level greater than 30 dB, and not over 45 dB at 4 kHz.  Note that no restrictions are specified for frequencies above 4 kHz.  In general, Service members with H1 hearing profiles are considered to be fully qualified for all military occupations.  However, certain occupations, like Air Traffic Control, Aviation, and Special Forces, may have more stringent standards.

• H2 Profile:  The H2 profile indicates a moderate hearing loss, which in the Army is defined as an individual who does not meet the H1 profile standards but has a pure tone average in each ear of no more than 30 dB, with no individual level greater than 35 dB at 0.5, 1, and 2 kHz, and not over 55 dB at 4 kHz.  In the Army, individuals who are monaurally deaf also qualify for H2 status, so long as they are able to meet a slightly more stringent audiogram requirement in the functional ear.  Individuals with H2 profiles are monitored more carefully and counseled on the principals of hearing conservation, but they are still generally considered to be fully qualified for most military occupations.  This may be an issue in occupations that require listeners to be able to accurately localize sounds to successfully complete their missions.

• H3 Profile:  An H3 profile, the worst of the three profiles, is assigned when a listener’s audiometric thresholds do not meet the requirements for the H2 profile, and the speech reception threshold in the best ear is not greater than 30 dB HL when measured with or without hearing aids.  An H3 profile will also be assigned if acute or chronic ear disease is present.  These profiles vary slightly for each Service branch of the military.  A Service member with either an H3 profile or a significant threshold shift relative to a previous audiometric testing requires a diagnostic audiogram.  Soldiers with H3 hearing levels are referred to the Military Occupational Specialty (MOS) Administrative Retention Review (MAR2) for a determination of their qualification to perform their MOS in a deployed environment or field condition.  The audiologist provides a recommendation to the MAR2 based on the diagnostic evaluation, a 200-word Speech in Noise Test known as the SPRINT, and the number of years in service for the individual Service member.  The MAR2 will make one of three decisions: 1) retain the Soldier in their current MOS; 2) re-classify the Soldier to a more suitable MOS; or 3) refer to the Disability Evaluation System (DES) for possible removal from military Service. 

8.  Where did the current hearing profile standards come from?

That’s a great question.  The documentation on the origin of the current standards, and the rationale used to determine the cutoff values between the different profile levels, are somewhat murky at this point.  The US Army fitness-for-duty regulation (AR 40-501) from 1987 uses almost exactly the same standard as the current cutoff between the H2 and H3 profiles (pure tone average at 0.5, 1, and 2 kHz of no more than 30 dB, with no single frequency greater than 35 dB, and no greater than 55 dB at 4 kHz), except that it also included an additional requirement for an audiogram with no more than 35 dB at 3 kHz.  So the current standards have been around at least 30 years.  But I don’t know exactly how the original profile cutoffs were established. 

9.  Are you okay with these standards?

Not entirely. Since 2009, we have been working on a project with the Army Hearing Program Office at the US Army Public Health Command to validate the current auditory fitness for duty standards and make recommendations for any changes that might be necessary to improve the hearing profile system in the military.  This effort has been greatly augmented by our partnership with the DoD Hearing Center of Excellence.  This center was established by Congress in Fiscal Year 2009 to serve as a military-wide advocate for addressing hearing loss and other auditory injuries being suffered by our nation’s Service members and Veterans.  Our goal is to develop comprehensive, validated auditory fitness for duty measures that both accurately reflect the impact that hearing loss is likely to have on operational effectiveness and are efficient enough to be assessed clinically on the scale required for an organization as large as the Department of Defense.

10.  Have your efforts resulted in any changes to the hearing standards so far?

Yes.  One of our first initiatives was to conduct analysis on the SPRINT (the speech test I mentioned earlier) that is currently used to assess the hearing abilities of US Army personnel with audiograms that place them in the H3 profile.  The military audiology community was concerned about the amount of time required to administer the test, which often exceeded 20 minutes.  By conducting an item analysis on the SPRINT, we were able to determine that it was possible to cut down the number of words from 200 to 100 with very little loss in the predictive power of the test.  The new SPRINT₁₀₀ was approved for use Army-wide in 2013, and hundreds of CDs of the new test and instruction booklets have now been distributed by the US Army Public Health Command. 

11.  Sounds like something I need to check out.  I’ve had several reservists needing the SPRINT show up in my clinic.  Do you think the SPRINT will eventually be used for evaluating speech in noise performance across all the Services?

It is possible, but we believe there may be some better alternatives.  We are in the process of evaluating other speech tests that might do a better job than the SPRINT at differentiating those Service members who are most likely to have difficulty communicating in militarily relevant environments.  As you know, there are some currently-available speech in noise tests that use adaptive procedures to measure a speech reception threshold, rather than a percent correct measure.  We are also considering the use of a closed-set test such as the Modified Rhyme Test (MRT).  The MRT requires listeners to choose words from sets of six alternatives that differ only by a single consonant (House, 1965).  One nice feature of the MRT is that it is currently used to evaluate the performance of military radios and other communication systems on listeners with normal hearing. As a result, there is some documentation of the intelligibility level that is required to achieve “acceptable” levels of communication effectiveness with the MRT.  Closed set tests also have the advantage that they could eventually be implemented in an automated testing system such as what is currently used to do audiogram testing in the military.

12.  Once you have somone's pure tone thresholds and the SPRINT results, how do you decide whether his or her hearing loss is severe enough to recommend reassignment or even separation from military Service?

Figuring out the threshold values to use for making recommendations about accession, retention, reassignment, and separation is the most difficult part of the development of a fitness for duty standard.  The greatest weakness of the current standard is that nobody really understands the thought process that went into setting those limits.  One possible approach to this problem is to simply set the thresholds at the bottom 5^th percentile of normal performance.  This approach has been used in occupations like law enforcement to establish standards for accession and retention (California POST, 2001).  However, there is really no way to know whether individuals who fail to meet the 5^th percentile of normal performance are really at risk if they are retained in their current positions.  Likewise, an individual who performs slightly better than the 5^th percentile of normal performance cannot be guaranteed “fit for duty”.  Our goal is to develop recommendations that are directly linked to the negative impact a hearing loss is likely to have on a Service member’s ability to perform his or her job in the field.

13.  There must be some cases where hearing is critical for performing military operations?

Yes, definitely.  The ability to detect, identify, and localize sounds, and to communicate effectively in noise and over degraded radio channels, is absolutely essential for a broad range of military operations.  The DoD Hearing Center of Excellence has just finished a project focused on identifying hearing-critical jobs in the military.  The results of this investigation found that all military specialties required hearing, but that some relied more on hearing-critical tasks than others.  In a deployed environment, any specialty requires critical hearing tasks.  For example, Service members in the infantry need to be able to communicate over a radio and to follow verbal orders over a communication system as well as to detect, identify and localize sounds.  This ability keeps them safe, efficient and effective.  Some hearing characteristics for hearing-critical tasks include sound detection, sound identification, sound localization, and speech recognition.  Occupational specialties in aviation also involve many hearing-critical tasks because of the critical role that radio transmissions play in communication with other aircraft and ground personnel.  Tactical command and control of aircraft and aviation support activities that are heavily reliant on radio communications.  Shipboard operations involve internal communication systems such as sound powered phones and afloat operations personnel must be able to respond to alarms and announcements made over the main circuit system.  Operations that involve heavy and light armored vehicles utilize communication systems between tank vehicles to produce voice and firing commands.  These are just a few examples of where hearing is absolutely critical for performing military operations. 

14.  Those are compelling cases, but have a lot of experiments been conducted to explicitly measure the relationship between hearing ability and operational performance in these military environments?

Not as many as we would like.  One of the first studies to look at this directly was an experiment conducted by Garinther and Peters (1990) in the Conduct of Fire Trainer (COFT) tank simulator at Fort Knox, KY.  They used 30 experienced tank crews to conduct gunnery scenarios under varying communication (speech intelligibility) conditions ranging from very good to very poor.  Their results were eye-opening. Their data showed reductions in speech intelligibility systematically increased the amount of time required for a tank crew to identify and destroy a target, which led to an increase in the number of times the crew was destroyed by the enemy.  The number of times the tank crew destroyed the wrong target also increased.  Since the Garinther and Peters study, a number of other studies have been conducted to evaluate the impact of hearing impairment on operational performance.  All have shown results similar to those in the Ft. Knox study, namely that reduced intelligibility translates to poorer operational success.  However, their results were not tied directly to a Service member’s hearing loss. Clearly, this is an area that requires more research.

15. How can you tie those kinds of operational performance measures back to the kinds of clinical tools we can use to measure an individual’s hearing in an audiometric test booth?

Good question—it’s a two pronged approach, really.  First, we need to measure actual military critical sounds in the field, and determine how well hearing impaired listeners are able to understand those auditory signals.  One way we are doing this is by mounting custom binaural recording devices on the cameramen who are embedded with combat units during exercises at the Joint Readiness Training Center in Ft. Polk, LA.  These cameramen are able to pick up the audio of critical signals that occur on the battlefield, like a shouted voice in a firefight saying that an insurgent has been seen in the upper-left window of a building.  By playing these signals back at their original levels to military personnel with varying levels of hearing loss we will be able to determine how much hearing loss can be tolerated before these critical signals become unintelligible to the impaired listener.  This can then be correlated back with the audiogram and with their scores on a clinical speech in noise test to try to make a prediction of operational performance.

16.  But how will you know how well they need to understand those sounds to complete the mission?

That is a really tough problem.  Our approach to this issue is to use hearing loss simulation systems, which can simulate different levels of hearing loss, so that we can systematically impair a normal listener’s hearing ability.  Then we can have these listeners perform operational tasks while wearing these hearing loss simulation devices and map the curve between operational performance and the amount of hearing impairment.  As a first step, we have begun employing this approach in a series of paintball-based combat simulations where we are attempting to directly measure the relationship between the amount of hearing loss an individual has and their survivability and lethality on the battlefield.  In these studies, we recruit active duty military personnel to play different game-variants of paintball while wearing custom helmet-mounted hearing loss simulators that we can program with different hearing profiles.  One variant where we’ve been collecting data is an every man for himself scenario played in the woods.  The instructions are simply to use the paint marker to eliminate all the other players from the field while avoiding being eliminated yourself (think “Hunger Games”).  This particular scenario emphasizes the impact of non-verbal auditory cues like localizing gunfire or hearing your enemy’s footsteps.  Each player is programmed with a different hearing profile and we keep track of the number of opponents that each player eliminates and the length of time that each player survives.  This allows us to compare differences in lethality and survivability as a function of hearing impairment.  We are also working on some variants of the paintball scenario that require participants to work together as a team in order to evaluate the impact of hearing loss of communication. 

17. And who said research can’t be fun?  But different individuals might have different levels of skill in these operational tasks.  How do you account for that?

True. But we play several rounds with the same group of players - as many rounds as there are hearing loss profiles being tested.  And the hearing profile assignments are switched after every round, such that each player completes one round with each of the different hearing loss profiles.  That way, the effect of individual skill or experience is balanced out.  The other variant we’ve been testing is a team vs. team capture-the-flag scenario in a semi-urban terrain.  In this variant a point would be played where one team has, say, a severe-to-profound hearing loss and the other team is assigned to be normal hearing, and then the hearing conditions are switched between the teams for the next point.  That way, each team would play an equal number of points with each of the two hearing profiles being compared.  This accounts for differences in overall skill level. 

18.  So, what have you found so far in these studies?

Initially, we expected to see results similar to those from the Garinther and Peters study, showing that impaired hearing leads to a systematic decrease in both how long players survive in the game and how many other players they were able to eliminate.  But what we hadn’t fully accounted for is the changes in behavior that occur when an individual is placed into a combat situation with hearing loss.  For example, in the last-man-standing scenario, as hearing acuity decreases, participants may lean toward a strategy that emphasizes survival over eliminating the opposition.  This is indicated by the fact that measures of survivability are minimally affected by hearing impairment, but a significant decrease in lethality is observed, where participants with a profound hearing impairment eliminate about half as many opponents as do listeners with normal hearing.  In other words, when hearing acuity is greatly diminished, participants may tend to cower and hide, which can be effective in this particular scenario, but may compromise the mission objective in other real-world situations. 

We are also applying the same simulating hearing loss approach to a variety of other military tasks, including squad communication in a firefight, command and control in a Navy Aegis Missile Cruiser, and additional paintball tasks that have more focus on team communication rather than individual action. 

19.  It sounds like you have a lot going on.  What is your plan for tying this all together in to a single recommendation for revised auditory fitness for duty standards?

This issue of auditory fitness for duty in the military is clearly too complex to ever exhaustively address even with a lifetime of studies.  Our approach right now is to focus on a series of validation studies we hope to conduct by measuring audiometric data, speech in noise performance, spatial awareness, and operational hearing performance on a large number of Service members who are visiting the audiology clinic to obtain their annual hearing screenings.  This is a large undertaking, but we hope to do it as efficiently as possible by using a data collection system based on an android tablet. The tablet can be handed to Service members who agree to participate in the study once they have completed their hearing exam.  These tablets will run a 5-10 minute speech in noise test and an additional 10-15 minutes of tasks involving operational noise environments.  For example, the tasks may include listening to speech recordings from the radio in a noisy vehicle or shouted speech communication on a crowded street with many chanting villagers.  We are working with the DoD Hearing Center of Excellence to get this infrastructure in place at several sites across the United States. Once we do that, we hope to obtain validation data from a large population of listeners.  After those data are acquired, we will run a regression analysis to attempt to predict the combination of audiometric threshold and speech in noise score that is required to ensure a high level of confidence that a hearing-impaired Service member will be able to hear and understand what they need to in order to be effective in the conduct of military operations.  The results from our hearing loss simulation studies will be instrumental in this process as well.  They will help us determine how well critical signals need to be heard in order to ensure adequate performance in a variety of military tasks. 

20.  Once you make those recommendations, will you be finished with the auditory fitness-for-duty problem?

We will have made a significant milestone in that direction, but there are many issues that still need to be resolved and will require further research.  In no particular order, here are five of them that immediately come to mind.

• One issue is the problem of how to manage auditory fitness-for-duty evaluations for individuals who can benefit from the use of hearing aids, cochlear implants, middle-ear implants, or other auditory prosthetics.  Headphone-based tests of the kind currently used for fitness-for-duty evaluations may interact in unpredictable ways with these devices, so a free-field test may be necessary.  However, in an organization as large as the US Military, it may be difficult to set up free-field test environments in a consistent way on the scale needed to accomplish AFFD evaluations. It's considerably more difficult to obtain valid and reliable measures in the soundfield compared to under earphones.  This may be an even bigger challenge in the future, because we are now looking at ways that military hearing protection devices and other tactical hearing systems can incorporate amplification and other features that might improve the operational performance of Service members with or without hearing loss.

• A second related issue concerns the importance of evaluating localization accuracy as part of a fitness for duty evaluation.  There is little doubt that sound localization is an important skill in many military tasks, but there are challenges involved in developing localization tests that can be consistently administered across a large number of test sites.  The challenges are due to both the expense of setting up these systems and to issues with room acoustics and other factors that might cause performance to vary from test location to test location.
   
•  A third challenge is dealing with central auditory processing problems in individuals who have normal audiograms.  These individuals complain of abnormal difficulty understanding speech in noise and generally dealing with complex auditory environments.  This seems to be an increasingly common problem in individuals who have been exposed to an explosive blast (Gallun, 2012).  These individuals would not be differentiated from other H1 individuals with the audiometric screening tools currently used to monitor hearing performance in the military population, so they pose a particular difficulty to the development of robust AFFD programs.
   
• Another issue involves the development of vestibular fitness-for-duty standards, which are particularly important for making judgments about the flight status of pilots who are experiencing dizziness or balance problems.  There are currently no standards that tie together the results from current state-of-the-art measures of clinical function (e.g. rotary chair testing) to the impact a particular issue may have on spatial disorientation in flight. 
   
• Finally, we would be remiss in not mentioning the greatest and most important challenge in military audiology, which is to find a way to prevent hearing loss from occurring in Service members altogether.  We are working on the development of advanced hearing protection systems that are more comfortable and maintain situational awareness better than current systems.  Also, the results of many of our operational tests of hearing are helping to guide the development of standards to evaluate the performance of hearing protection systems. This includes things like determining how well an individual needs to localize sounds with a hearing protection device, for example. The results of this work will help ensure that our military personnel are receiving the equipment that best meets their needs.

References

California POST (2001). California Peace Officer Standards and Training Hearing Guidelines.  lib.post.ca.gov/Publications/Hearing.pdf

Department of the Army (2008).  ST4-02.501: Army Hearing Program, https://militaryaudiology.org/site/wp-content/images/st_4_02_501.pdf

Gallun, F. J., Lewis, M. S., Folmer, R. L., Diedesch, A. C., Kubli, L. R., McDermott, D. J., ... & Leek, M. R. (2012). Implications of blast exposure for central auditory function: A review. Journal of Rehabilitation Research & Development, 49(7).

Garinther, G.R., & Peters, L.J. (1990).  Impact of communications on armor crew performance:  investigating the impact of noise and other variables on mission effectiveness.  Army Research, Development Acquisition Bulletin (January/February), 1-5. 

Hearing Center of Excellence (2014).  Military hearing critical task review by service. 

House, A. S., Williams, C., Hecker, M. H., & Kryter, K. D. (2005). Psychoacoustic speech tests: A modified rhyme test. Journal of the Acoustical Society of America, 35(11), 1899-1899.

McIlwain, D. S., Gates, K., & Ciliax, D. (2008). Heritage of army audiology and the road ahead: the Army Hearing Program. American Journal of Public Health,98(12), 2167.

Tufts, J.B., Vasil, K.A., & Briggs, S. (2009).  Auditory fitness for duty: A review.  Journal of American Academy of Audiology, 20, 539-557.