Acceptable Noise Level - Update 2012

Melinda Freyaldenhoven Bryan, Ph.D., CCC-A, Assistant Professor, Louisiana Tech University, AudiologyOnline Contributing Editor - Adult Amplification

Jessica Leigh Ann Newman, B.A., 4th year resident, Veterans Health Administration, North Little Rock, AR

Introduction

To review, Nabelek, Tucker, and Letowski (1991) introduced a procedure for determining acceptable noise intensities while listening to speech. This procedure has come to be known as acceptable noise level (ANL). The ANL procedure quantifies a listener's willingness to listen to speech in the presence of background noise. To obtain an ANL conventionally, a recorded story of running speech (currently available from Frye Electronics) is adjusted to the listener's most comfortable listening level (MCL). Next, background noise is added and adjusted to a level that the listener is willing to put up with while listening to and following the words of a story (called background noise level or BNL). The ANL, in dB, is calculated by subtracting the BNL from the MCL (ANL = MCL - BNL). ANL is typically measured with both the speech and background noise presented at 0 degrees azimuth.

Previous research shows that ANLs are reliable and normally distributed in listeners with both normal and impaired hearing (Nabelek, Tampas, & Burchfield, 2004; Freyaldenhoven & Smiley, 2006; Freyaldenhoven, Smiley, Muenchen & Konrad, 2006; Nabelek, Freyaldenhoven, Tampas, Burchfield & Muenchen, 2006). Furthermore, previous research has shown that unaided ANLs may be related to hearing aid use. Specifically, individuals who can accept high levels of background noise (i.e., have low ANLs, no greater than 7 dB) are more likely to wear hearing aids on a regular basis (i.e., become full-time hearing aid users). Conversely, individuals who accept low levels of background noise (i.e., have high ANLs, greater than 13 dB) are less likely to wear hearing aids regularly (i.e., become part-time users or nonusers of hearing aids). Furthermore, unaided ANLs can predict a listener's success with hearing aids (i.e., hearing aid use/acceptance) with 85% accuracy (Nabelek et al, 2006; see Freyaldenhoven, 2007, for the curve displaying the probability of success with hearing aids).

ANLs obtained at Multiple Speech Presentation Levels

As stated previously, conventionally ANLs are measured at the listener's MCL. ANLs have also been measured non-conventionally at multiple speech presentation levels. Previous results in listeners with normal hearing demonstrated that ANLs were related to speech presentation level. Specifically, a 4 dB increase in speech presentation level yielded a 1 dB increase in ANL. These results indicated that ANL is related to the presentation level of the speech stimuli but that a relatively large change in speech level was required to affect an ANL (Franklin, Thelin, Nabelek, & Burchfield, 2006).

Freyaldenhoven, Plyler, Thelin, and Hedrick (2007) continued this work through the investigation of the effects of speech presentation level on ANLs in participants with normal (n=30) and impaired (n=69) hearing. ANLs were obtained conventionally (i.e., at participants' MCL) and at eight fixed speech presentation levels (i.e., 40, 45, 50, 55, 60, 65, 70, and 75 dB HL). Then, global ANL (i.e., ANL average at the fixed speech presentation levels) and ANL growth (i.e., slope of the ANL function determined through linear regression analysis) were calculated. Statistical analysis revealed no significant difference for global ANL or ANL growth between listeners with normal and impaired hearing. Furthermore, global ANL and ANL growth results did not correlate with participants' pure tone average. These results indicate that the effects of speech presentation level on ANLs are not affected by hearing sensitivity. Lastly, data analysis did show a significant correlation between conventional ANLs and participants' global ANL and ANL growth, indicating that participants' conventional ANL is related to their global ANL and ANL growth data (Freyaldenhoven et al., 2007).

Furthermore, Freyaldenhoven, Plyler, Thelin, and Muenchen (2008) measured the effects of speech presentation levels on ANLs for three groups of participants in an attempt to predict hearing aid use. Using the Pattern of Hearing Aid Use Questionnaire (Nabelek et al., 2006), participants were categorized into one of the three groups: full-time hearing aid users (N = 25); part-time hearing aid users (n = 21); and non-hearing aid users (N = 23). ANLs were measured conventionally and at eight fixed speech presentation levels (40, 45, 50, 55, 60, 65, 70, and 75 dB HL). Global ANLs (i.e. averages of ANLs at the eight speech presentation levels) and ANL growth (i.e., slope of the ANL function) were calculated. The results revealed that conventional and global ANLs were significantly smaller in full-time hearing aid users than conventional and global ANLs for part-time and non-hearing aid users; however, conventional and global ANLs were not significantly different between part-time and non-hearing aid users. The results also revealed that ANL growth differentiated full-time users from non-users only. These results indicate global ANLs differentiated full-time hearing aid users from part-time and non-users, but cannot differentiate part-time and non-users of hearing aids. This is the same way that conventional ANLs differentiate the hearing aid groups. Data analysis also revealed that conventional ANLs predicted successful versus unsuccessful hearing aid use with 68% accuracy. Lastly, the predictive value of ANLs measured at fixed speech presentation levels were evaluated because ANLs measured at these levels should be quicker for clinical use. The results showed that the predictive value for ANLs measured at 65 dB HL was comparable to the predictive value of ANLs measured conventionally, indicating that ANLs may be able to be measured at a fixed speech presentation level (i.e., 65 dB HL) and used to predict hearing aid use (Freyaldenhoven, Nabelek & Tampas, 2008).

ANL as a Predictor of Hearing Aid Use

Taylor (2008) investigated the predictive value of ANL as compared to self-reported hearing aid benefit/satisfaction. Twenty-seven first-time, binaural hearing aid users with sensorineural hearing loss served as participants for this study. The following pre-fitting procedures were completed: pure tone audiogram testing, word recognition in quiet, unaided QuickSIN, and conventional ANL. Participants were then fit with binaural hearings aids with wide dynamic range compression parameters utilizing standard fitting protocols. Approximately 30 days post-fitting participants were asked to complete the International Outcome Inventory for Hearing Aids (IOI-HA) questionnaire in order to evaluate their self-reported hearing aid performance in a real-world setting. The IOI-HA test questions were divided into two sub-test factors. Factor 1 questions evaluated the participants' introspection of their hearing aids (i.e., "me and my hearing aid") while Factor 2 questions evaluated the participants' interactions with the outside world environment. Furthermore, the participants were divided into the following three groups based on their ANL score: Group 1: low ANL score, 0 to 6 dB (n=16); Group 2: moderate ANL score, 7 to 12 dB (n = 7); Group 3: high ANL score, 13 dB or greater (n=4). Results of the study revealed that all three groups reported positive outcomes with amplification. Furthermore, the results revealed a significance relationship between unaided ANL and both the overall IOI-HA score and the IOI-HA Factor 1 questions (i.e., intrinsic factors). Analysis did not reveal a significance relationship for the unaided ANL as related to the IOI-HA Factor 2 questions (i.e. outside world factors). These results indicated that as the overall IOI-HA score worsened, ANLs tended to increase (i.e., become poorer). The same relationship was seen for the Factor 1 questions; as the answers to the Factor 1 questions became smaller (i.e., worsened), ANL tended to become poorer. Based on these results the research concluded that unaided ANLs measured pre-hearing aid fitting could be a potential and valid predictor of hearing aid benefit/satisfaction (Taylor, 2008).

In 2008, Freyaldenhoven, Nabelek, and Tampas examined the relationship between ANLs and the Abbreviated Profile of Hearing Aid Benefit (APHAB) and their combined ability to predict hearing aid use. Study participants (n=191) were divided into the following groups based on hearing aid use: full-time hearing aid users (n=69), part-time hearing aid users (n=69), and non-users of hearing aids (n=53). Testing procedures included the following: pure tone audiometric testing, unaided ANLs, aided ANLs for participants that were hearing aid users, and completion of the APHAB. Results of this study concluded that there was not a significant correlation between unaided and aided ANLs and unaided, aided, or benefit scores on the APHAB, indicating that ANLs and these scores of the APHAB provide different information regarding hearing aid use/satisfaction. Furthermore, results of the study revealed that the Ease of Communication (EC) and Background Noise (BN) subscales of the APHAB predicted hearing aid use/satisfaction with 61% and 60% accuracy, respectively. In combination, ANLs, BN, and EC subscales increased the accuracy of prediction from 85% using ANL alone to 91%. Furthermore, three of the APHAB subscales (EC, BN, and Reverberation) increased the prediction of hearing aid use in participants with mid-range ANLs (i.e., patients whose probability of success is hardest to predict based on ANL alone). Conclusively, these results indicate that the APHAB in combination with ANL measurements can be beneficial in providing information on hearing aid outcome and use, especially for those who have mid-range ANLs (Freyaldenhoven et al., 2008).

Effects of Speech Stimulus on ANL Results

Gordon-Hickey and Moore (2008) investigated the effects of intelligible, reversed, and unfamiliar primary discourse (i.e., Chinese language) on acceptance of noise in 30 participants with normal hearing and no familiarity with the Chinese language. Female participants were solely used for the purpose of this study due to previous research indications that gender may affect MCL findings. The following stimuli were utilized in this study: intelligible speech, reversed speech, and unfamiliar speech (i.e., Chinese). MCL and BNL measurements were obtained for each participant in all three conditions, and conventional ANLs were calculated. The results revealed similar/non-significant average MCLs in the intelligible (M=51.5 dB HL), reversed (M=51.4 dB HL), and the unfamiliar (M= 53.4 dB HL) conditions. Results of the study also revealed a significant change in BNLs and the resulting ANLs when changing the intelligibility of the primary discourse. Specifically, ANLs were lower (i.e., better) when using intelligible speech and background noise versus when the speech and background noise were unintelligible (i.e., reversed speech and speech of a different language). Results of this study indicated that participants were much more accepting of background noise when the stimulus was intelligible than when it was unintelligible (i.e., reversed or an unfamiliar language). In conclusion, ANLs may become poorer as degradation of the speech stimulus occurs and/or as speech recognition abilities decrease in normal hearing listeners (Gordon-Hickey &Moore, 2008).

Plyler, Alworth, Rossini, and Mapes (2011) investigated the effects of speech content and/or speaker gender on the acceptance of background noise in participants (n = 43, male = 26, female = 17) with normal hearing. For the purposes of this study, a male and female recording of the Arizona Travelogue (Cosmos Inc.) and the Ipsilateral Competing Message (ICM) from the Synthetic Sentence Identification with ICM (SSI-ICM) was created and utilized. Speech and noise were both presented from the same loudspeaker at 0o azimuth for four different conditions: Arizona Travelogue male, Arizona Travelogue female, ICM male, and ICM female. Two ANLs were obtained for each condition following the conventional clinical protocol for obtaining ANLs. Furthermore, 21 of the 43 participants completed an interest level evaluation in which they were asked to rate their interest level in the speech sample in both quiet and noise. The interest level evaluation was ranked on a five-point scale ranging from (1) = not at all interested to (3) = interested to (5) = extremely interested. Results of the interest level rating indicated that overall interest levels were significantly higher in the ICM speech samples than the Arizona Travelogue. In addition, interest levels were significantly greater for speech samples spoken by female voices as opposed to male voices. Interestingly, results further revealed that neither speaker gender nor the content of the speech signal significantly affected MCL or ANL values in normal hearing listeners. In conclusion, these results indicated that various types of speech and background noise signals can be utilized to measure ANLs clinically, at least in listeners with normal hearing (Plyler et al., 2011).

Effects of Hearing Aid Directionality and Noise Reduction on ANL Results

Lowery (2009) examined the influence of noise reduction technology settings on participants' (n=30) ANLs. Three noise reduction technologies were evaluated: directional microphones (D-Mic), digital noise reduction algorithms (DNR), and a combination of D-Mic and DNR (called Combo). The following background noise conditions were used as stimuli for each condition: single talker speech, speech shaped noise, and multi-talker speech babble. Participants were fit with two Siemens, Artis 2 S/VC behind-the-ear (BTE) hearing aids with the following four memories: no noise reduction (baseline), D-Mic only, DNR only, and Combo. Conventional ANLs were measured. In addition, participants were asked to complete subjective preference rankings in each condition. It should be noted that for analysis purposes ANL benefit scores were calculated for each of the noise reduction conditions by subtracting the ANL for the test condition from the baseline ANL score (e.g., ANL for DNR - no noise reduction/baseline ANL). The results revealed lower (i.e., improved) ANLs for the Combo noise reduction condition as opposed to the DNR and D-Mic only conditions. Listeners also yielded lower (i.e., improved) ANLs for the D-Mic condition compared to those obtained with DNR condition. These results indicated that listeners accepted the most background noise when directional microphones were used in combination with DNR technologies. Secondly, the use of directional microphones alone allowed for more background noise acceptance when compared DNR technologies used in isolation. Furthermore, when the background noise was speech-like (i.e., single or multi-talkers), participants preferred the D-Mic and Combo conditions more than the DNR condition; however, the Combo condition was preferred when the listener was in the presence of speech shaped noise. Collectively, these results indicated acceptance of background noise was maximized and preferred when directional microphones were used alone or in combination with DNR technologies in hearing aids, especially when the background noise was speech (Lowery, 2009).

Ahlstrom, Horwitz, and Dubno (2009) evaluated the spatial benefit of bilateral hearing aids. Specifically, one purpose of this study was to evaluate the effect of noise source location on ANL. Sentences were always presented at 0° azimuth and babble was either presented at 0° (i.e., spatially coincident) or 90° (i.e., spatially separated) azimuth. Results of the study found that participants' ANLs improved when aided speech and babble were spatially separated, indicating that participants accepted more babble when the babble and speech were spatially separated. In other words, ANLs varied based on the location of the noise source (i.e., 0° versus 90°). Lastly, significant correlations were found between aided, spatial benefit for ANLs and aided, spatial benefit for HINT sentences, indicating an association between the ANL and HINT measures (Ahlstrom et al., 2009).

Kim and Bryan (2011) investigated the effects of asymmetric directional microphone fittings on ANLs and speech understanding in noise in 15 participants with bilateral, symmetrical sensorineural hearing loss. Binaural Siemens Intuis BTE hearing aids with twin microphones (i.e., fixed hypercardioid polar plot) were fitted on each participant. Speech understanding in noise (completed using the Hearing in Noise Test; Nilsson, Soli & Sullivan, 1994) and acceptance of background noise (completed using the ANL procedure) were evaluated in the following four conditions: binaural omnidirectional, right asymmetric directional (i.e., directional microphone on the right ear and omnidirectional microphone on the left ear), left asymmetric directional (i.e., directional microphone on the left ear and omnidirectional on the right ear), and binaural directional. Speech in noise testing revealed a significant improvement when participants were fitted with either right or left asymmetric directional or binaural directional microphones, as compared to omnidirectional microphones. However, no difference in speech in noise scores was found when comparing right and left asymmetric directional microphone fittings to binaural directional microphones. These results indicate that speech understanding in noise improves when utilizing both the right and left asymmetric directional microphones compared to binaural omnidirectional microphones; however, speech understanding in noise performance is not hindered when comparing the right and left asymmetric directional microphone conditions to binaural directional microphones. Furthermore, results of the study revealed that participants had improved (i.e., lower) ANLs in the two asymmetric directional microphone conditions when compared to using binaural omnidirectional microphones. Furthermore, participants had further improved (i.e., lower) ANLs for the binaural directional condition when compared to the two asymmetric directional microphone conditions. These results indicate acceptance of background noise (i.e., willingness to wear hearing aids) improved for the asymmetric directional microphone conditions as compared to the binaural omnidirectional condition and is maximized in the binaural directional condition. Because speech in noise is not hindered when using asymmetric directional microphones and acceptance of background noise improved, the authors concluded that asymmetric directional microphones might be a practical options for those unable or unwilling to switch hearing aid microphone programs (Kim & Bryan, 2011).

ANL Findings in Cochlear Implant Users

Plyler, Bahng, and Hapsburg (2008) evaluated the following: ANLs in participants with cochlear implants (CI, n=9) in comparison to participants with normal hearing (n=15); if ANLs are correlated with speech reception thresholds (SRT) in noise for cochlear implant users; and if ANLs and subjective outcome measures are related in cochlear implant users. Conventional ANL measurements were used to evaluate acceptance of background noise, and the HINT was utilized to evaluate participants' speech understanding in noise. The APHAB and a satisfaction questionnaire were given to the CI users to compare their level of satisfaction with their previous hearing aids to their current cochlear implant. Results of the study revealed that MCLs and ANLs were not significantly different between normal hearing participants and CI users. The results also revealed that ANLs are not directly related to speech understanding in noise abilities or APHAB scores in participants with normal hearing or CI users. Lastly, ANLs in CI users were significantly correlated with overall CI benefit on the satisfaction questionnaire, indicating ANL testing may be a potential aid in determining satisfaction with cochlear implants (Plyler et al., 2008).

Donaldson et al. (2009) investigated the ability of speech recognition in noise using the Bamford-Kowal-Bench Sentences in Noise test (BKB-SIN) and ANLs to predict communication ability reported on the APHAB in CI users. CI users (n=20) were asked to complete the APHAB to rate their communication difficulty before implantation (i.e., with hearing aids) and after implantation. Participants' communication difficulty rating using the APHAB was compared to participants' speech recognition in noise using the BKB-SIN. Results of this comparison revealed that participants with poorer speech recognition in noise (BKB-SIN) demonstrated a larger frequency of self-perceived communication problems using the APHAB. The relationship between ANL and APHAB scores for CI users was also evaluated. Results indicated a significant relationship between ANL and APHAB scores. Specifically, participants with larger ANLs (i.e., poorer tolerance for background noise) showed higher APHAB scores (i.e., higher frequency of perceived communication problems). Collectively, these results revealed that ANLs and BKB-SIN scores predicted approximately three-fourths (73%) of the variance in global APHAB scores. Furthermore, results of the study indicated that the BKB-SIN results and ANLs can be a valuable clinical tool in assessing CI users' self-perceived communication ability (Donaldson et al., 2009).

Effects of High Frequency Filtering and Reverberation on ANLs

Plyler, Madix, Thelin, and Johnston (2007) investigated the influence of high frequency information (i.e., beyond 2000Hz) on ANLs in participants with normal hearing (n=20) and impaired hearing (n=20). MCLs, BNLs, and calculated conventional ANLs were measured using speech and background noise that was unfiltered and low-pass filtered at 2000, 4000, and 6000 Hz. Group data showed that information beyond 2000 Hz did not significantly affect, improve or degrade ANLs in most participants with normal and impaired hearing. Individual data analysis, however, revealed that access to information beyond 2000 Hz did affect ANLs for some participants. Specifically, 35% (i.e., 14 of 40) of participants showed a 3 dB or greater change in MCLs and ANLs relative to the unfiltered condition, suggesting that information beyond 2000 Hz may change (i.e., improve or degrade) some listeners acceptance of background noise (Plyler et al., 2007).

Johnson, Ricketts, and Hornsby (2009) investigated the effect of extending the high frequency bandwidth of speech and background noise on ANL. Furthermore, the effects of reverberation time and spectral shape of the background noise were examined. Fifteen listeners with symmetrical, mid-to-moderate SNHL completed a modified ANL procedure in 27 experimental conditions (3 bandwidths × 3 reverberation times × 3 background noise shapes). The three bandwidths included a low-pass filtered frequency bandwidth at 3000, 6000, and 9000 Hz while reverberation times of 308, 708, and 1425ms were utilized. Results of the study revealed that there was a significant increase in ANLs (i.e., ANLs worsened) when the high frequency bandwidth was extended from 3000 to 9000 Hz and from 6000 to 9000Hz. Furthermore, reverberation time and spectral shape of the background noise showed no significant effect on ANLs. Interestingly, there was a significant interaction between the spectral shape of the background noise and reverberation time, in that ANLs were larger (i.e., worse) when reverberation time was short and background noise was most speech-like as compared to when the background noise was more noise-like and reverberations times were long. Based on these results, the authors cautioned readers regarding extending bandwidths in hearing aids and the negative effect that it might have on acceptance of background noise, especially when the background noise is speech-like. Specifically, extending bandwidths in hearing aids beyond 6000 Hz may decrease acceptance of background noise, which may decrease hearing aid success/use (Johnson et al., 2009).

Adams, Gordon-Hickey, Moore, and Morlas (2010) evaluated the effects of reverberation on ANL in 12 younger adults (age: 22-29 years) and 12 older adults (age: 50-69 years) with essentially normal hearing. Five conditions were created to produce varying amounts of reverberation times (i.e., RT = 0, 0.4, 0.7, 1.2, and 2s), which was applied to both the primary discourse and the background noise. Then each participant's MCL, BNL, and calculated conventional ANL were determined. The results revealed no significant effect for age and/or reverberation time on MCL or ANL findings. These results indicated that neither reverberation time nor age affects the level of the speech selected nor the amount of background noise a person is willing to accept (Adams et al., 2010).

ANLs in Children

Moore, Gordon-Hickey, and Jones (2011) compared MCLs, ANLs, and BNLs in children (8-10 years) and young adults (19-29 years) with normal hearing. Results of the study revealed that there was no significant difference in ANLs between the two groups (i.e., adults versus children). Results further revealed that there was a significant difference for MCLs and BNLs for children and adults. Specifically, MCLs and BNLs were significantly higher for the adult population as compared to those obtained for children. Overall, the results indicated that ANLs are essentially unchanged from childhood to adulthood; however, differences in MCLs and BNLs were reported between groups (Moore et al., 2011).

Furthermore, Jones and Moore (2011) evaluated acceptance of background noise and speech perception in noise in children with normal hearing (n=16) and children with bilateral hearing impairment (n=16). Speech perception in noise was evaluated utilizing the Hearing in Noise Test-Children (HINT-C), and acceptance of background noise was evaluated using the conventional ANL procedure. Results of the study revealed no significant difference between ANLs for children with normal and impaired hearing, indicating that ANLs are not related to hearing sensitivity in children. The authors further compared results from this study to previous ANL investigations completed using adults (Freyaldenhoven, Plyler, Thelin, & Burchfield, 2007; Nabelek et al., 2006; Nabelek et al., 1991) and found ANLs for children with normal and impaired hearing were similar to those obtained in adults. Based on these results, the authors suggested that ANLs are similar in children and adults and can therefore be used in similar manners (Jones & Moore, 2011).

Effects of Music Preference in ANL Findings

In 2007, Gordon-Hickey and Moore evaluated the effect of music and music preference on ANLs in listeners with normal hearing (n=24). The primary stimulus used was the male-speaker version of the Arizona Travelogue while the secondary stimuli included six different music stimuli (all from the rock genre) and twelve-talker babble. Following testing, participants were given an exit questionnaire to evaluate familiarity with the music sample and overall enjoyment of the music used. The results revealed that ANLs obtained using music were significantly better than for ANLs obtained using multi-talker babble. The results also showed a significant correlation/relationship between ANLs obtained with multi-talker speech babble and ANLs obtained using music. These results indicated that participants were more willing to accept music as a background noise than multi-talker babble. The authors further noted that the trend between ANLs obtained with multi-talker babble and music remains consistent; therefore, if a listener has a low ANL for multi-talker babble, they also have a low ANL if obtained with music as the background noise stimuli. Lastly, results of the study revealed that participants' music preference and familiarly with the music sample was not directly related/correlated to the listener's ANL (Gordon-Hickey & Moore, 2007).

ANL Findings in Individuals with Hypercusis

In 2011, Levy, Peck, and Balachandran evaluated the effect of hyperacusis on conventional ANLs by comparing listeners with normal hearing and no report of hyperacusis (n=7) to those with hearing loss and reported hyperacusis (n=7). Testing procedures included pure tone air conduction testing (500-8000 Hz), loudness discomfort levels (LDLs), DPOAEs, ANLs, and a hyperacusis questionnaire. Preliminary data analysis revealed that ANLs for normal hearing listeners (M = 1.1 dB) were lower than ANLs obtained for listeners with hyperacusis (M = 6 dB). Furthermore, results of this study demonstrated that ANL evaluation may be beneficial in aiding in the identification of individuals with hyperacusis.

Summary

In summary, ANL is a procedure used to quantify listeners' willingness to listen to speech in the presence of background noise. Foremost, recent research has been completed on the relationship of ANLs as a predictor of hearing aid use. Specifically, ANLs may be able to be measured at a fixed speech presentation level and used to predict hearing aid use (Freyaldenhoven, Plyler, et al., 2008). Furthermore, unaided ANLs measured pre-hearing aid fitting may be a valid predictor of hearing aid benefit/satisfaction (Taylor, 2008). Lastly, the APHAB used in combination with ANL can be beneficial in providing information on hearing aid outcome and use (Freyaldenhoven, Nabelek, et al., 2008).

Research has also been completed to evaluate the effects of speech stimulus on ANLs. Research shows that ANLs may become poorer as degradation of the speech stimulus occurs and/or as speech recognition abilities decrease in normal hearing listeners (Gordon-Hickey & Moore, 2008). Furthermore, speaker gender or the content of the speech signal does not appear to affect MCL or ANL values in normal hearing listeners (Plyler et al., 2011).

Furthermore, the current review discussed the relationship of hearing aid directionality, noise reduction, filtering, and reverberation on ANL results. Lowery (2009) found that acceptance of background noise was maximized and preferred when directional microphones were used alone or in combination with DNR technologies in hearing aids, especially when the background noise was speech. Ahlstrom et al. (2009) found that participants' accepted more noise when the speech and babble were spatially separated (i.e., babble was at the side and speech was in front). Furthermore, Kim and Bryan (2011) reported that acceptance of background noise improved when using an asymmetric directional microphone fitting as compared to an omnidirectional microphone fitting. Plyler et al. (2007) found that access to information beyond 2000 Hz did not affect ANLs for most listeners; however, individual data analysis showed that about 35% of the participants showed a 3 dB or greater change in MCLs and ANLs relative to the unfiltered condition. Furthermore, Johnson et al. (2009) found that extending bandwidths in hearing aids beyond 6000 Hz may decrease acceptance of background noise. Lastly, research has shown that neither reverberation time, spectral shape of the background noise, nor age has an effect on background noise acceptance (Johnson et al., 2009; Adams et al., 2010).

The current review also discussed research related to ANLs in children and ANLs in cochlear implant users. Moore et al. (2011) found that ANLs in children and adults are similar. Jones and Moore (2011) further reported similar ANLs for children with normal and impaired hearing. Furthermore, Plyler et al. (2008) found that ANLs were not different between normal hearing participants and CI users. Lastly, Levy et al. (2011) stated that a ANL evaluation may be beneficial in aiding in the identification of individuals with hypercusis.

References

Adams, E.M., Gordon-Hickey, S., Moore, R.E., & Morlas H. (2010). Effects of reverberation on acceptance noise level measurements in younger and older adults. International Journal of Audiology, 49, 832-838.

Ahlstrom, J.B., Horwitz, A.R., & Dubno J.R. (2009). Spatial benefit of bilateral hearing aids. Ear and Hearing, 30(2), 203-218.

Donaldson, G.S., Chisolm, T.H., Blasco, G.P., Shinnick, L.J., Ketter, K.J., & Krause, J.C. (2009). BKB-SIN and ANL to predict perceived communication ability in cochlear implant users. Ear and Hearing, 30(4), 401-410.

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

Freyaldenhoven, M.F. (2007). Acceptable Noise Level (ANL): Research and current application. AudiologyOnline, Article 1756. Article retrieved December 12, 2011, from www.audiologyonline.com/articles/article_detail.asp?article_id=1756

Freyaldenhoven, M.C., Plyler, P.N., Thelin, J.W., & Hedrick, M.S. (2007). The effects of speech presentation level on acceptance of noise in listeners with normal and impaired hearing. Journal of Speech, Language, and Hearing Research, 50, 878-885.

Freyaldenhoven, M.C., Plyler, P.N., Thelin, J.W., & Muenchen, R.A. (2008). Acceptance of noise growth patterns in hearing aid users. Journal of Speech, Language, and Hearing Research, 51, 126-135.

Freyaldenhoven, M.C., Nabelek, A.K., & Tampas, J.W. (2008). Relationship between acceptance of noise level and the abbreviated profile of hearing aid benefit. Journal of Speech, Language, and Hearing Research, 51, 136-146.

Freyaldenhoven, M.C., Smiley, D.F. (2006). Acceptance of background noise in children with normal hearing. Journal of Educational Audiology, 13, 27-31.

Freyaldenhoven, M.C., Smiley, D.F., Muenchen, R.A., & Konrad, T.N. (2006). Acceptable noise level: reliability measures and comparison to background noise preference. Journal of the American Academy of Audiology, 17, 640-648.

Gordon-Hickey, S., & Moore, R.E. (2007). Influence of music and music preference on acceptable noise levels in listeners with normal hearing. Journal of the American Academy of Audiology, 18, 417-427.

Gordon-Hickey, S., & Moore, R.E. (2008). Acceptance of noise with intelligible, reversed, and unfamiliar primary discourse. American Journal of Audiology, 17, 129-135.

Johnson, E., Ricketts, T., & Hornsby, B. (2009). The effect of extending high-frequency bandwidth on the acceptable noise level (ANL) of hearing-impaired listeners. International Journal of Audiology, 48, 353-362.

Jones, A.L. & Moore, R.E. (2011, April). Acceptable noise levels and speech perception in noise for children. Poster session presented at the annual meeting of Audiology Now!, Chicago, IL.

Kim, J.S., & Bryan, M.F. (2011). The effects of asymmetric directional microphone fittings on acceptance of background noise. International Journal of Audiology, 50, 290-296.

Levy, M., Peck, T., & Balachandran, R. (2011, March). Acceptable noise levels in hyperacusic individuals. Powerpoint presentation retrieved December 12, 2011 from www.ata.org/sites/ata.org/files/pdf/Acceptable_Noise_Levels_in_Hyperacusic_Individuals.pdf.

Lowery, K. (2009). The effects of noise reduction technologies on the acceptance of background noise. Unpublished doctoral dissertation, University of Tennessee-Knoxville.

Moore, R., Gordon-Hickey, S., and Jones, A. (2011). Most comfortable listening levels, background noise levels, and acceptable noise levels for children and adults with normal hearing. Journal of the American Academy of Audiology, 22, 286-293.

Nabelek, A.K., Freyaldenhoven, M.C., Tampas, J.W., Burchfield, S.B., & Muenchen, R.A. (2006). Acceptable noise level as a predictor of hearing aid use. Journal of the American Academy of Audiology,17, 626-639.

Nabelek, A.K., Tampas, J.W., & Burchfield, S.B. (2004). Comparison of speech perception in background noise with acceptance of background in aided and unaided conditions. Journal of Speech, Language, and Hearing Research, 47, 1001-1011.

Nabelek, A.K., Tucker, F.M., & Letowski, T.R. (1991). Toleration of background noises: Relationship with patterns of hearing aid use by elderly persons. Journal of Speech and Hearing Research, 34, 679-685.

Nilsson, M., Soli, S.D., & Sullivan, J.A. (1994). Development of the Hearing in Noise Test for the measurement of speech reception thresholds in quiet and in noise. Journal of the Acoustical Society of America, 95(2), 1085-1099.

Plyler, P.N., Alworth, L.N., Rossini, T.P., & Mapes, K.E. (2011). Effects of speech signal content and speaker gender on acceptance of noise in listeners with normal hearing. International Journal of Audiology, 50(4), 243-248.

Plyler, P.N., Bahng, J., & Hapsburg, D.V. (2008). The acceptance of background noise in adult cochlear implant users. Journal of Speech, Language, and Hearing Research, 51, 502-515.

Plyler, P.N., Madix, S.G., Thelin, J.W., & Johnston, K.W. (2007). Contribution of high-frequency information to the acceptance of background noise in listeners with normal and impaired hearing. American Journal of Audiology, 16, 149-156.

Taylor, B. (2008). The acceptable noise level test as a predictor of real-world hearing aid benefit. The Hearing Journal, 61(8), 39-42.