20Q: Acceptable Noise Level Test - Supporting Research and Clinical Insights

From the Desk of Gus Mueller

It is often tempting to place hearing aid candidates into convenient buckets, based on nothing more than their audiogram and their age.  Imagine two different patients - both 70-year-old males, with downward-sloping bilateral hearing losses going from 30 dB at 500 Hz to 70 dB at 4000 Hz.  In many clinics and offices, these two patients will be fitted with the same hearing aids, with the same features activated, with the same accessories, and they will receive the same orientation and post-fitting counseling.  But what is the probability that these two patients really should be treated the same?

Gus Mueller

We know that patients of the same age with the same hearing loss can have large differences in their ability to understand speech in background noise.  Their listening needs also might be quite different.  And they likely will have different expectations, and probably personalities, too.  Their cognitive abilities may be very different. And, what about their acceptance of background noise?  This is yet another factor that can’t be predicted from the patient’s hearing loss (or age, or gender).  Will this impact success with hearing aids?  Many people believe that it will, and one of them is this month’s 20Q author. 

A handy test to assess a patient’s acceptance of background noise is the Acceptable Noise Level test, or ANL—a quick speech-in-noise test that easily can be administered.  There is probably no one who has studied this test as much as our guest author, Patrick Plyler, PhD, professor in the Department Audiology and Speech Pathology at the University of Tennessee, and Director of the UT Hearing Instrument Research Laboratory.  

Dr. Plyler got us started thinking about the ANL in last month's 20Q when he talked about the test administration and interpretation.  He’s back this month with our Question Man, answering questions related to the background research surrounding this intriguing test.  In just the past 10 years, there have been dozens of publications reporting research findings with the ANL—if you haven’t had the time to read them all, you’ll find the results of most of them in this great review article.

 

 

Gus Mueller, PhD

Contributing Editor

July, 2015

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

 

 

20Q: Acceptable Noise Level Test - Supporting Research and Clinical Insights

Patrick Plyler

1. Thanks for all the information last month.  Ready for a new round of questions?

Ready when you are.

2.  Last time, you mentioned that ANL values are not related to how well one performs on speech recognition tasks.  Isn’t the ANL just another speech-in-noise test?  

It is important to understand that speech-perception-in-noise testing and acceptance of background noise testing simply provide different information about the patient. One would assume that performance on these tests would be related; however, multiple studies have compared results for different speech-perception-in-noise tests (e.g., SPIN, HINT, QuickSIN) to the ANL, and consistently there has been no significant correlation.  One patient could have a very good HINT score (e.g., + 2 dB) but their ANL could be very large (e.g., 15 dB) and vice versa. 

One interesting study compared three speech tests available to clinicians: QuickSin, ANL, and the Performance-Perceptual Test (PPT).  The goal was to determine if each test provided unique information regarding a patient or, because of common associations between the tests, were results of one test predictive of results on the other tests.  Interestingly, the findings suggested each test provided useful, non-associative information about a patient.  The authors concluded each test added unique information that could be used for counseling or possibly for decision making regarding technology (Weber, Mueller, & Johnson, 2010). 

Other research has compared the contributions of both speech in noise and ANL results to hearing aid outcome (Nabelek, Freyaldenhoven, Tampas, & Burchfield, 2006; Freyhaldenhoven, Plyler, Thelin, & Muenchen, 2008; Plyler, Bahng, & von Hapsburg, 2008.)  Findings suggested speech-in-noise tests are excellent tools for demonstrating hearing aid benefit, but are less effective at predicting hearing aid use. Thus, it is important to understand the purpose of the ANL test.

 3.  Interesting.  Are ANL values related to individual characteristics such as degree of hearing loss or age? 

Great question.  Interestingly, however, research suggests individual factors that commonly impact speech perception tests do not affect ANL values.  Although one would assume that listeners with better hearing would accept more noise than listeners with more hearing loss, this is not the case, as ANL values are not higher (worse) for listeners with more hearing loss than those with less hearing loss (Nabelek, Tucker, & Letowski, 1991; Freyaldenhoven, Plyler, Thelin, & Hedrick, 2007; Plyler et al., 2008).  In addition, ANL values do not appear to increase with age (Nabelek et al., 1991; Nabelek et al., 2006; Freyaldenhoven & Smiley, 2006) and are similar for males and female listeners.

4.  Not to sound sexist, but since males are typically considered to be “tougher,” do they then tolerate noise at a higher level? 

We studied that at the University of Tennessee several years ago (Rogers, Harkrider, Burchfield, & Nabelek, 2003).  The results of this research revealed that indeed, the background noise level (BNL) for males was slightly higher than the BNL for females, but the male’s MCL also was higher, and as a result, the ANLs were the same for males and females.

5.  What about characteristics of the stimuli?  Are ANL values related to the type of speech used?  

Early ANL projects actually used a female speaker reading an excerpt from On Walden Pond by Thoreau. More recent studies have relied on a male speaker reading a passage with very different content, commonly referred to the Arizona Travelogue.  Comparison of ANL values across these studies suggests that the type of speech stimuli used may not matter that much; however, the effect of the content and/or speaker gender of the speech stimulus on the ANL had not been tested within the same participant cohort.  We speculated a listener may accept less noise if the content of the speech was deemed to be interesting or important to the listener.  That is, a listener may tolerate less noise if listening to a football game on the radio versus a weather report.  On the other hand, the content of the speech could have no impact on ANL values as research suggests noise acceptance is not related to speech understanding.

So, we created a male and female recording of both the Arizona Travelogue and the competing message from the synthetic sentence identification (SSI) test  (Speaks & Jerger, 1965).  The Arizona Travelogue is the standard speech sample currently used for ANL testing.  The SSI competing story was selected because we believed the content (life story of Davy Crockett) was potentially more interesting to our listeners here in Tennessee.  In the end, the SSI competing message was deemed to be more interesting to the listeners; however, neither the content of the speech nor the gender of the speaker affected the MCL or the ANL values (Plyler, Alworth, Rossini, & Mapes, 2011).  Recent research was in agreement with this finding suggesting any change in ANL due to speaker gender was small and not clinically significant (Gordon-Hickey, Moore, & Estis, 2012).  Nonetheless, the use of the commercially available standard speech stimuli is recommended (the Arizona Travelogue with male speaker), as this allows clinicians and researchers to compare their findings to published normative data (Nabelek et al., 2006).

6.  What about the background noise?

In the initial research, Dr. Nabelek evaluated the impact of the noise type on the ANL (termed tolerated noise level at the time).  ANLs were obtained using 5 different noises: speech spectrum noise, 12-talker babble, traffic noise, a pneumatic drill, and music.  The findings suggested the type of background noise had no impact on the ANL with one exception: ANLs were significantly worse (larger) when music served as the background noise (Nabelek et al., 1991).  A more recent study further examined the role of music on the ANL and found the opposite: ANLs were significantly better when music served as the background noise (Gordon-Hickey & Moore, 2007).  So, if measuring ANLs without hearing aids, it may be best to avoid using music as the background noise.

Importantly, early ANL research suggested ANL values do not change when tested with and without hearing aids, possibly due to the fact the original ANL work was conducted with hearing aids without digital noise reduction (DNR) and many without directional microphones.  Recent studies suggest noise type can impact aided ANL measures if digital noise reduction (DNR) algorithms are being used.  Namely, hearing aids with DNR systems activated can improve ANL values when the background noise is steady-state, like the HINT noise for example (Mueller, Weber, & Hornsby, 2006; Lowery & Plyler, 2013).  As with the speech stimuli, we recommend use of the noise that is present on the commercially available ANL test, (twelve-talker babble), as this allows clinicians and researchers to compare their findings to published normative data (Nabelek et al., 2006).

7.  Would there be any reason to conduct the testing at different fixed presentation levels rather than the patient’s MCL? 

As stated earlier, it is very important to follow the instructions and procedures suggested by Dr. Nabelek.  Otherwise, you are conducting a modified ANL and your results may be inaccurate and unreliable.

That being said, research shows ANL values are related to speech presentation levels in both listeners with normal and impaired hearing (Franklin, Thelin, Nabelek, & Burchfield, 2006; Tampas & Harkrider, 2006; Freyaldenhoven et al., 2007).  Namely, ANL values increase (get worse) as the level of the speech signal increases, and this level effect is larger for patients with high ANL values versus those with low ANL values (Tampas & Harkrider, 2006; Freyaldenhoven et al., 2007).  The observed difference in ANL growth rates suggests listeners may use loudness as a cue to determine their ANL; however, Recker and colleagues (2014) demonstrated this was not the case in listeners with normal or impaired hearing.  Furthermore, ANL growth patterns are similar in listeners with normal hearing and cochlear hearing loss, thereby suggesting that ANL values may be mediated beyond the peripheral auditory system (Tampas & Harkrider, 2006; Freyaldenhoven et al., 2007).

8.  Can you elaborate on "beyond the peripheral auditory system?"

Several studies have examined the impact of the peripheral and central auditory nervous system on individual ANL values.  ANL values were not related to acoustic reflex thresholds or to otoacoustic emissions in normal hearing listeners (Harkrider & Smith, 2005).  Interestingly, normal hearing listeners with poor noise acceptance (ANLs >16 dB) had shorter auditory brainstem response latencies and larger middle and late latency response amplitudes than normal hearing listeners with excellent noise acceptance (ANLs <6 dB).  These researchers speculate that central efferent mechanisms may be weaker and/or central afferent mechanisms may be more active in listeners with large versus small ANLs (Tampas & Harkrider, 2006).  A similar result was obtained when using speech evoked auditory potentials (Shetty, Mahadev, & Veeresh, 2014) and listeners with impaired hearing (Tampas, 2007).  At any rate, it appears that acceptance of noise may be centrally meditated.

9.  We all have some patients who just seem to be less tolerant of everyday events in general. Is it possible noise acceptance is related to a patient’s personality?  

Possibly. In the initial ANL study in 1991, Dr. Nabelek proposed that acceptance of noise could be inherent to an individual.  Years later, we examined the relationship between noise acceptance and personality in normal hearing listeners, as personality is also considered an inherent characteristic.  As you might expect, listeners with Type A personality had significantly higher ANL values than listeners with Type B personality (Alworth, Plyler, & Madix, 2007).  In a separate study, acceptance of noise was also shown to be significantly related to self control.  Normal hearing listeners with higher levels of self-control accepted more noise than those with lower levels of self control (Nichols & Gordon-Hickey, 2012).  Thus, research does support Dr. Nabelek’s earlier thought that acceptance of noise may be inherent to an individual in some regards.

10.  Let’s get practical for a moment. What if a patient has a really high ANL?  Are you suggesting they will be an unsuccessful hearing aid user, so don't bother?

Absolutely not. However, a patient with a really high ANL value will be more likely to reject the hearing aids, regardless of their aided speech understanding benefit.  By measuring the unaided ANL, you can identify these patients early on in the process and provide additional counseling and tools to assist with noise.  For example, a patient with a really high ANL value may be much more dependent on noise reduction technologies that can improve their acceptance of noise.  Many of these features are now “standard,” but it’s still important for you to consider their sophistication, strength levels and benefits when used in combination.  

11.  What sort of things should I be thinking about regarding noise reduction options?

Noise reduction technologies may be particularly helpful for patients with mid-range ANLs (9 to 12 dB).  Research indicates that directional microphones can improve a patient’s ANL by approximately 4 dB (Freyaldenhoven, Nabelek, Burchfield, & Thelin, 2005; Lowery & Plyler, 2013).  A patient with an unaided ANL of 10 has a 45% chance of being a successful hearing aid user (Nabelek et al, 2006).  However, if using hearing aids with directional microphone technology reduces the aided ANL by 4 dB, the patient's probability of becoming a successful hearing aid user improves significantly.  Keep in mind a patient with a high ANL (above 12 dB) will likely improve as well, but probably not enough to become a successful user.  I should note, however, that these studies were contrived to determine if directionality improved acceptance of noise under ideal conditions (a study of efficacy). ANL improvements observed with directional microphones in the laboratory may or may not generalize to more real-world environments.

12.  That sounds great.  I would assume DNR algorithms may be helpful as well, right?

Yes, it appears that DNR and directionality have a similar impact on the ANL.  In fact, research suggests DNR can improve a listener's ANL by an average of around 4 dB as well (Mueller et al., 2006; Lowery & Plyler, 2013).  Now, these studies evaluated a DNR system with both a modulation-based algorithm and a fast-active noise cancelling system.  Results could differ when using a DNR system with a modulation-based algorithm only, since many of these DNR systems only engage when the speech-to-noise ratio is negative (noise is greater than the speech).  If patients needing the most noise reduction have higher (positive) ANL values, it is possible the modulation-based DNR systems would rarely engage, thereby not affecting background noise acceptance very much (there could be some channel-specific effects for certain noises).  Studies also suggest the type of background noise impacts the effect of DNR on the ANL as DNR is more effective for steady-state noises and less effective for noises containing “speech-like” patterns (Lowery & Plyler, 2013).  

Although the use of DNR is common-place in modern hearing aid fittings, the effects could vary substantially across DNR systems and background noise types encountered.  In fact, I recall attending a presentation by Dr. Ruth Bentler at the American Academy of Audiology Convention many years ago where she demonstrated the significant performance differences of 10 dB or more across DNR systems in hearing aids in reaction to different types of input (Bentler & Chiou, 2006).  In addition, DNR systems vary in terms of the amount of reduction and in terms of the time required to engage.  Thus, clinicians should be aware that the impact of DNR on the ANL test could vary quite a bit across hearing aids, so the best bet is to measure the effect of the DNR in the test box, using probe-microphone measures during the fitting, or behaviorally in the clinic. Of course, with nearly all fittings, the patient will experience the combined effects of DNR and directional technology, and our laboratory study revealed that this can improve the ANL by an average of almost 8 dB (Lowery & Plyler, 2013). Again, the benefit may not be this great in real-world environments.

13.  Earlier you said ANL values do not change over time and may be inherent to an individual.  Now you say noise reduction technologies can improve an ANL.  Isn’t this contradictory? 

First, recall these noise reduction strategies were evaluated under ideal test conditions.  When the conditions are perfect, noise reduction technologies assess the acoustic scene and engage, thereby requiring increased noise levels to reach the individuals physiologic "noise threshold (BNL)."  Consequently, the calculated ANL value is reduced.  However, these features are not physiologically moving the hearing aid user's "noise threshold."  The reason that the ANL is better is because the SNR in the earcanal changed, not because the peripheral or central auditory system changed.   In the future, auditory training techniques could be developed to physiologically change noise acceptance.  If so, patients with poor ANL values may need training to improve their noise acceptance either prior to or during the hearing aid trial.

14. Would the use of noise reduction technologies potentially improve hearing aid use patterns?

While the impact of noise reduction technologies on ANL is promising, what remains unclear is if these findings translate to real-world settings.  Studies are needed that evaluate the role of these technologies on hearing aid use.  Would patients with mid-range ANL values that may reject hearing aids need more aggressive forms of directionality and DNR in order to become full-time hearing aid users? Good question.  If changes in hearing aid outcome are impacted by ANL improvement with these features, then attempting to improve an ANL would clearly be a worthy goal.

15.  I know some hearing aids have extended high frequency amplification and/or frequency lowering.  Could either of those improve an ANL?

No, it may actually make matters worse.  Although increasing access to high-frequency information improves speech understanding, keep in mind the ANL is not a measure of speech understanding per se.  Consequently, high-frequency information either has no impact on ANL values in listeners with normal or impaired hearing (Plyler, Madix, Thelin, & Johnston, 2007) or can actually make ANL values worse. Johnson, Ricketts, and Hornsby (2009) evaluated the effect of extending high-frequency bandwidth on ANL values in listeners with mild sensorineural hearing loss.  Results showed that ANL values actually became poorer when high-frequency bandwidth was extended from 3 to 9 kHz and from 6 to 9 kHz.  

I am unaware of any published research examining the effect of frequency lowering on the ANL.  That being said, we have collected data in my laboratory at The University of Tennessee examining the effect of frequency compression on speech understanding in noise and acceptance of noise in 15 adult hearing aid users.  Results indicated frequency compression did not impact either measure.

16.  How do ANL values relate to other measures of hearing aid benefit and satisfaction? 

The relationship between ANL values and traditional measures of hearing aid benefit and satisfaction are a bit mixed.  For example, unaided ANL values are related to the final outcome via the International Outcome Inventory for Hearing Aids (IOI-HA).  Specifically, the ANL accounted for 32% of the variance  observed for the Factor 1 variables on the IOI-HA (“me and my hearing aid”) (Taylor, 2008).  Similarly, a study in Taiwan also compared results on a Taiwanese version of the ANL test to hearing aid success assessed 3 months post-fitting using the IOI-HA as well.  Results revealed that ANL results were significantly associated with hearing aid outcomes, with higher ANLs suggesting poorer outcomes (Ho, Wu, Hsiao, & Zhang, 2013).   Conversely, ANL values are not related to outcome via the Abbreviated Profile of Hearing Aid Benefit (APHAB), suggesting that each measure provides unique information regarding hearing aid use (Freyaldenhoven, Nabelek, & Tampas, 2008). 

17.  Is noise acceptance impacted by visual cues?

Yes.   In a recent study in my laboratory, we found that the addition of visual cues improved ANL values for normal hearing listeners; however, visual cues only improved ANL values for listeners with impaired hearing when they were using their hearing aids.  In other words, visual cues did not improve unaided ANL values but did improve aided ANL values.  Interestingly, the impact of visual cues on the ANL was larger for listeners with poor ANL values than those with good ANL values; however, it was not related to speech reading ability (Plyler, Lang, Monroe, & Gaudiano, in press).  These results were consistent with previous studies examining the role of visual cues on the ANL in normal hearing listeners (Plyler & Alworth, 2008; Wu, Stangel, Pang, & Zhang, 2014).  Thus, future research should evaluate if an audio-visual ANL test provides a more accurate measure of noise acceptance and serves as a better predictor of hearing aid use.

18.  I know we’re focused on hearing aids, but before we finish I have to ask—Can you use the ANL test with cochlear implant patients too? 

Well, the ANL test should not replace speech-in-noise tests for CI patients; however, I believe it can be useful for those that cannot complete the understanding tasks.  We compared ANL values and HINT scores in 20 normal hearing listeners and in 9 adult cochlear implant users.  HINT results were much poorer for the CI group than the normal hearing group, as one would expect.  Interestingly, ANL values were similar between the groups.  Also, CI listeners that reported the most subjective benefit, were those with the poorest (highest) ANL values.  This finding seemed somewhat "backwards" at first, but these listeners reported greater problems with their old hearing aids and had more room for benefit (Plyler et al., 2008).  Similar findings were reported from a group of 21 adult CI users and 23 listeners with normal hearing (Donaldson et al., 2009). 

In addition, the ANL test has been used to demonstrate benefit from a noise reduction algorithm designed for cochlear implant processing.  Twenty adult CI users were tested with and without the noise reduction feature using the ANL test and tests of speech understanding in noise.  Results indicated the noise reduction feature had no impact on speech understanding in noise but did significantly improve noise acceptance (Dingemanse & Goedegebure, 2014).  Taken together, these studies suggest the ANL test may be useful when assessing CI patients.    

19.  Way back when you mentioned that the ANL can predict hearing aid success with 85% accuracy.  That  seems like wishful thinking to me.  Have other studies attempted to substantiate this in the real-world?

Great point.  Dr. Nabelek cautioned readers in her 2006 seminal paper that the 85% accuracy could be an over-estimate because statistical models fit data upon which they were developed better than they fit a new set of data.  Consequently, one would expect a lower prediction accuracy when using similar analyses in clinical practice.  In fact, studies conducted around the world routinely show that successful hearing aid users (defined in various ways) have lower ANL values than unsuccessful users.  That being said, studies typically report a “real-world” predictive value lower than 85%, which is what Dr. Nabelek expected.  It should be noted, however, that few studies have a sample size as large as the Nabelek et al. (2006) study.  In addition, the proportion of full-time and non-users of hearing aids in the original ANL study was consistent with hearing aid use rates reported in the literature at the time (Kochkin, 2002a; Kochkin, 2002b).  In recent research, often times studies do not have a representative number of hearing aid rejecters or primarily examine experienced hearing aid users (Olsen, Lantz, Nielsen, & Brannstrom, 2012).  I think an often overlooked facet of the ANL model is the fact that the most common unaided ANL value in listeners with hearing loss is 10 dB, which corresponds to a predicted success rate of around 50%.  We can all agree that there are many ways to define “success” in terms of hearing aid outcomes.  When evaluating the ANL test and predictive value, however, it is important to understand that Dr. Nabelek defined success using the hearing aid questionnaire she developed.  That is how she defined “success” when creating the ANL test and prediction model.  Consequently, it shouldn’t be too surprising that the ANL test is less accurate at predicting success when success is defined using other more commonly used outcome measures.    

20.   You and your colleagues at the University of Tennessee have been studying ANL for almost 20 years.  What future directions do you think this research will take?

We are excited to see that the ANL is becoming studied on an international level.  Since the original paper was published, more than 50 research papers have been dedicated to the ANL test.  Many researchers have created ANL tests in multiple languages across the globe.  Although the ANL test is often misunderstood, I am hopeful future research will explore improving the ANL test as well developing a better understanding of the mechanisms underlying acceptance of noise.  

References

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Bentler, R. & Chiou, L. (2006). Digital noise reduction: An overview. Trends in Amplification,10, 95-104.

Dingemanse, J., & Goedegebure, A.  (2014).  Application of noise reduction algorithm ClearVoice in cochlear implant processing: effects on noise tolerance and speech intelligibility in noise in relation to spectral resolution.  Ear & Hearing, 36, 357-367.

Donaldson, G., Chisolm, T., Blasco, G., Shinnick, L., Ketter, K., & Krause, J.  (2009). BKB-SIN and ANL predict perceived communication ability in cochlear implant users.  Ear & Hearing, 30, 401-410. 

Franklin, C., Thelin, J., Nabelek, A., & Burchfield, S.  (2006).  The effect of speech presentation level on acceptance of background noise in normal-hearing listeners.  Journal of the American Academy of Audiology,17,141–146.

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Tampas, J. & Harkrider, A. (2006).  Auditory evoked potentials in females with high and low acceptance of background noise when listening to speech. Journal of the Acoustical Society of America, 119,1548–1561.

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Wu Y., Stangl E., Pang C., & Zhang X. (2014) The effect of audiovisual and binaural listening on the acceptable noise level (ANL): Establishing an ANL conceptual model.  Journal of the American Academy of Audiology, 25,141-153.