Yearly Archives: 2010

Considerations for Directional Microphone Use in the Classroom

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Directional Benefit in Simulated Classroom Environments

Ricketts, T., Galster, J. and Tharpe, A.M. (2007)

This editorial discusses the clinical implications of an independent research study. The original work was not associated with Starkey Laboratories and does not reflect the opinions of the authors.

Classroom acoustic environments vary widely and are affected by a number of factors including reverberation and noise from within the classroom and adjacent areas. Signal-to-noise ratio (SNR) is known to affect speech perception for children with normal hearing and those with hearing loss (Crandell, 1993; Finitzo-Hieber & Tillman, 1978). Because listeners with hearing loss typically require more favorable SNRs to achieve the same performance as normal hearing listeners, hearing-impaired students are particularly challenged by high levels of classroom noise.

FM systems are often recommended as a method for improving SNR in the classroom. However, they may not effectively convey voices other than the teacher’s, so children may be less able to hear comments or questions from other students.  The additional bulk of ear level FM systems may prompt reluctance to wear the FM system, as the student may perceive this as calling attention to their hearing loss.  Because of these and other potential limitations of FM systems, the use of hearing aids with directional microphones is an opportunity to improve SNR for hearing-impaired children.

The benefits of directional microphones for speech perception in the presence of background noise are well known for adults (Bentler, 2005; Ricketts & Dittberner, 2002; Ricketts, Henry & Gnewikow, 2003). Research has shown that children also benefit from directionality in laboratory conditions (Gravel, Fausel, Liskow & Chobot, 1999; Hawkins, 1984; Kuk, et al., 1999), but more information is needed on the effect of directional microphone use in classroom environments.  The study summarized in this post evaluated directional microphone use in simulated classroom situations and the subjective reaction to omnidirectional and directional modes by children and parents.

The authors recruited twenty-six hearing-impaired subjects ranging in age from 10-17 years participated in the experiment.  All but two had prior experience with hearing aids.  Subjects were fitted bilaterally with behind-the-ear hearing instruments that were programmed with omnidirectional and directional modes.  Digital noise reduction and feedback suppression features were disabled and all participants were fitted with unvented, vinyl, full-shell earmolds.

This study consisted of three individual experiments. The first investigated directional versus omnidirectional performance in noise in five simulated classroom scenarios:

1) Teacher Front – speech stimuli presented in front of the listener.

2) Teacher Back – speech presented behind the listener.

3) Desk Work – speech presented in front of the listener, the listener’s head oriented down toward desk

4) Discussion – three speech sources at 0 and 50-degree azimuth (left and right), simulating a round table discussion

5) Bench Seating – speech presented at 90-degree azimuth (left and right)

Speech recognition performance was evaluated in each of these scenarios using a modified version of the Hearing in Noise Test for Children (HINT-C, Nilsson, Soli & Sullivan, 1994). Speech stimuli were initially presented at 65dB SPL for the five test conditions. Noise was presented from four loudspeakers positioned 2 meters from each corner of the room. For conditions 1-3, the noise level was 55dB. For conditions 4 and 5, noise levels were fixed at 65dB.

A second experiment examined the performance of omnidirectional versus directional modes in the presence of multiple talkers. Monosyllabic words from the NU-6 lists (Tillman & Carhart, 1966) were randomly presented at 63dB SPL from speakers positioned 1.5 meters, surrounding the listener at three angles: 0 degrees (in front of listener), 135 degrees (back right) and 225 degrees (back left). Noise was presented at 57dB SPL, which again yielded an SNR of 6dB.

Not surprisingly, the results of the first experiment showed that directional performance was significantly better than omnidirectional performance for Teacher Front, Desk Work and Discussion conditions, but was significantly worse for the Teacher Back condition.  There was no significant difference between omnidirectional and directional modes for the Bench Seating condition.  In the Bench Seating condition, however, subjects were not specifically instructed to look at the speaker. If some subjects did look at the speaker and others did not, individual differences between omnidirectional and directional modes may have been obscured on average.  Improved performance was generally noted as the distance between speaker and listener decreased. This is consistent with previous studies with adult listeners, which showed increased directional benefit with decreasing distance (Ricketts & Hornsby, 2003, 2007).

The second experiment yielded no significant difference in performance between omnidirectional and directional modes when speech was in front of the listener. When speech was presented behind the listener, omnidirectional mode was significantly better than directional in both the back-right and back-left conditions.  The authors surmised that the directional benefit may have been reduced because subjects were told that all of the talkers were important and because 2/3 of the talkers were behind them, they may have been more focused on speech coming from the back.

The current study offers insight into the potential benefit of directional microphones for classroom environments. An FM system remains the primary recommendation for improving signal-to-noise ratio of a teacher’s voice, but overhearing other students and multiple talkers can be compromised by FM technology.  Additionally, because of social, cosmetic or financial concerns FM use may not be feasible for many students. Therefore, directional hearing instruments will likely continue to be widely recommended for hearing-impaired schoolchildren. This study reported a directional benefit ranging from 2.2 to 3.3 dB, which is consistent with studies of adult listeners (Ricketts, 2001).  Therefore, directional microphone use in classrooms may indeed be beneficial, as long as the teacher or speaker of interest is in front of the listener. However, for round table or small group arrangements, directionality could be detrimental, especially when talkers are behind the listener.  The authors point out that many school scenarios involve multiple talkers or speech from the sides and back, so directional microphone benefit may be limited overall.

The results of these experiments underscore the importance of counseling for school-age hearing aid users, as well as their parents and teachers. It is common practice to recommend preferential seating close to the teacher in the front of the classroom. Improved performance with decreases in distance from the speech source, in this and other studies, shows that this recommendation is particularly important for hearing aid users, whether or not they are in a directional mode. Furthermore, hearing-impaired students should be instructed to face the teacher so they can benefit from directional processing as well as visual cues. This should also be discussed in detail with teachers so that efforts can be made to arrange classroom seating accordingly.

An incidental finding of the first experiment showed that performance for the Desk Work condition was better than the Teacher Front condition, even though the distance between speaker and listener was comparable.  In the Desk Work condition, subjects were instructed to work on an assignment on the desk as they listened. Therefore, the listener’s head position was pointed slightly downward, which may have resulted in more optimal, horizontal positioning of the microphone ports, increasing directional effect. This finding demonstrates the importance of selecting the proper tubing or wire length, to position the hearing aid near the top of the pinna and align the microphone ports along the intended plane.

Overall, directional processing improved performance for speech sources in front of the listener and reduced performance for speech sources behind the listener. The instruments in this study were full-time omnidirectional or directional instruments, so it is unknown how automatic, adaptive directional instruments would perform under similar conditions. Because of the prevalence of automatic directionality in current hearing instruments, this is a question with important implications for school-age hearing aid users.  Perhaps automatic directionality could provide better overall access to speech in many classroom environments, but controlled study is needed before specific recommendations can be made.

References

Anderson, K.L. & Smaldino, J.J. (2000). The Children’s Home Inventory of Listening Difficulties. Retrieved from http://www.edaud.org.

Bentler, R.A. (2005). Effectiveness of directional microphones and noise reduction schemes in hearing aids: A systematic review of the evidence. Journal of the American Academy of Audiology, 16, 473-484.

Crandell, C. (1993). Speech recognition in noise by children with minimal degrees of sensorineural hearing loss. Ear and Hearing 14, 210-216.

Finitzo-Hieber, T. & Tillman, T. (1978). Room acoustics effects on monosyllabic word discrimination ability for normal and hearing-impaired children. Journal of Speech and Hearing Research, 21, 440-458.

Gravel, J., Fausel, N., Liskow, C. & Chobot, J. (1999). Children’s speech recognition in noise using omnidirectional and dual-microphone hearing aid technology. Ear and Hearing, 20, 1-11.

Hawkins, D.B. (1984). Comparisons of speech recognition in noise by mildly-to-moderately hearing-impaired children using hearing aids and FM systems. Journal of Speech and Hearing Disorders, 49, 409-418.

Kuk, F.K., Kollofski, C., Brown, S., Melum, A. & Rosenthal, A. (1999). Use of a digital hearing aid with directional microphones in school-aged children. Journal of the American Academy of Audiology, 10, 535-548.

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

Resnick, S.B., Dubno, J.R., Hoffnung, S. & Levitt, H. (1975). Phoneme errors on a nonsense syllable test. The Journal of the Acoustical Society of America, 58, 114.

Ricketts, T., Lindley, G., & Henry, P (2001). Impact of compression and hearing aid style on directional hearing aid benefit and performance. Ear and Hearing, 22, 348-361.

Ricketts, T. & Dittberner, A.B. (2002). Directional amplification for improved signal-to-noise ratio: Strategies, measurement and limitations. In M. Valente (Ed.), Hearing aids: Standards, options and limitations (2nd ed., pp. 274-346). New York: Thieme Medical.

Ricketts, T., Galster, J. & Tharpe, A.M. (2007). Directional benefit in simulated classroom environments. American Journal of Audiology, 16, 130-144.

Ricketts, T., Henry, P. & Gnewikow, D. (2003). Full time directional versus user selectable microphone modes in hearing aids. Ear and Hearing, 24, 424-439.

Ricketts, T. & Hornsby, B.( 2003). Distance and reverberation effects on directional benefit. Ear and Hearing, 24, 472-484.

Ricketts, T. & Hornsby, B.(2007). Estimation of directional benefit in real rooms: A clinically viable method. In R.C. Seewald (Ed.), Hearing care for adults: Proceedings of the First International Conference (pp 195-206). Chicago: Phonak.

Tillman, T. & Carhart, R. (1966). An expanded test for speech discrimination using CNC monosyllables (Northwestern University Auditory Test No. 6) SAM-TB-66-55. Evanston, IL: Northwestern University Press.

Comparing localization ability with BTE and CIC hearing aids

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A Comparison of CIC and BTE Hearing Aids for Three-Dimensional Localization of Speech

Best, V., Kalluri, S., McLachlan, S., Valentine, S., Edwards, B. & Carlile, S. (2010)

Localization of external sound sources is achieved in a number of ways.  In additional to visual cues, listeners use binaural time and intensity differences to localize sounds on a horizontal plane (Woodworth, 1938).  Monaural spectral cues provide additional information about vertical location and help differentiate sound sources that are in front of or behind the listener (Blauert, 1997). There is ample evidence that localization of sound sources may be an important first step in the perception of speech in complex listening environments (Freyman et al, 2001; Bregman, 1990; Arbogast et al, 2002). Several studies have shown that hearing aid users demonstrate poorer aided localization than when unaided (Noble & Byrne, 1990; Byrne et al., 1992; Keidser et al, 2006; Vanden Bogaert et al, 2006). This is thought to be due to disruption of binaural time and intensity cues by bilateral hearing aids. Therefore, monaural localization cues are valuable hearing aid wearers and may have particularly important implications for their ability to understand speech in noisy situations.

Two factors known to reduce the availability of monaural spectral cues are of particular relevance to hearing aid users: reduced audible bandwidth (Butler, 1986; Middlebrooks, 1992; Blauert, 1997) and sensorineural hearing loss (Byrne et al, 1992; Noble et al, 1994, 1997; Byrne & Noble, 1998; Rakerd et al, 1998).  These factors reduce spectral cue localization because of decreased audibility of high frequencies. Sensorineural hearing loss is accompanied by decreased frequency resolution, which can itself impair spectral cue localization (Jin et al, 2002).  Additionally, hearing aid users lose pinna-related spectral cues, particularly with behind-the-ear (BTE) models in which the microphone is placed above the pinna. Completely-in-the-canal (CIC) instruments are thought to preserve pinna-related spectral localization cues because of microphone placement at the ear canal entrance.

The purpose current study was to contrast spatial localization abilities in users with CIC and BTE hearing aids and normal hearing listeners. Two measures of localization were analyzed:

- Lateral localization (horizontal localization – left/right with reference to midline)

- Polar localization (encompassing up/down and front/back dimensions)

The authors recruited eleven subjects with mild to moderate sensorineural hearing loss and four subjects with normal hearing. Hearing-impaired subjects were fitted with CIC and BTE instruments.  All hearing instruments had 1.5 mm vents and both CIC and BTE instruments had bandwidth out to approximately 6800Hz. Directional microphones, noise reduction processing and environment classification features were disabled. Hearing aids were programmed to match CAMEQ  gain targets (Moore, 1999) and fittings were verified with real-ear measurements. Prior to localization testing, additional probe microphone measurements were conducted to determine aided audibility of the speech stimuli to be used in the test sessions.

Hearing-impaired subjects were tested with both CIC and BTE hearing instruments after a period of “accommodation” or acclimatization to each type of instrument. The experiment was therefore conducted in six phases:

1. Localization testing (both hearing aids)

2. Accommodation period (4-6 weeks, hearing aid A)

3. Localization testing (hearing aid A)

4. Accommodation period (4-6 weeks, hearing aid B)

5. Localization testing (hearing aid B)

6. Localization testing (unaided)

Subjects with normal hearing were tested under two conditions. In one condition, the speech was a broadband stimulus (up to 40,000Hz) and in the other it was low-pass filtered at 6800Hz to approximate the bandwidth of the hearing instruments worn by the hearing-impaired subjects.

Listeners were presented with monosyllabic words at an average level of 65dB for hearing-impaired listeners and 55dB for normal hearing listeners. Subjects were asked to “point their nose” toward the perceived location of the speech. Testing was completed in an anechoic chamber and head orientation was monitored with an electromagnetic tracking system.

The results indicated that for lateral localization errors, there was no difference between CICs and BTEs, no significant difference between aided and unaided results, nor was there a significant effect of accommodation. Performance for normal hearing subjects was more accurate than that of the hearing-impaired subjects.  There was a great deal of variability among hearing-impaired subjects; those with poorer low-frequency thresholds had increased lateral localization errors.  Previous studies have shown that aided lateral localization is usually worse than unaided and the authors surmised that the performance of the subjects in this study could have been related to their relatively good low-frequency hearing thresholds or the availability of airborne sound through the hearing aid vents.

Analysis of polar angle localization errors yielded similar results. There was no significant effect of hearing aid use, hearing aid style or accommodation. Performance was substantially better for normal hearing subjects, regardless of bandwidth condition, though errors were slightly greater for the limited bandwidth condition.  Although vertical localization in particular was expected to be related to the availability of high-frequency cues, no significant correlational was found for unaided individual performance and high-frequency pure-tone thresholds, or aided results and high-frequency aided sensation level.

Performance with CIC instruments yielded significantly fewer front/back reversals than performance with BTEs and results for both hearing aid types showed significant improvement after accommodation periods. Unaided responses were more accurate than either aided condition and subjects with normal hearing did better than hearing-impaired subjects in any condition. The front/back reversal rate was not correlated with high frequency audiometric thresholds or aided sensation levels, nor was the benefit of CICs over BTEs correlated with high Hz sensation level.  Previous research shows that front/back localization is primarily related to conchal resonance, which occurs around 4000-5000Hz (Hebrank & Wright, 1974). CIC microphone placement should allow for preservation of these cues, whereas BTE configurations would not.  Interestingly, unaided performance in the current study was still better than aided, despite the likelihood that cues in the 4000-5000Hz range would have been inaudible for these subjects without their hearing aids.

The results of this study indicate that hearing-impaired listeners are likely to experience some decreased sound localization ability relative to normal hearing listeners, regardless of hearing aid style.  The degree to which localization ability is affected may be related to audiometric thresholds, venting, directionality, compressions settings and other variables.  Though lateral and vertical localization was not affected by hearing aid microphone location in this study, CIC instruments afforded better front/back localization than BTE devices.  It is possible that new hearing aid technology will allow for enhanced spectral cue availability.  For instance, improvements in feedback control allow more stable high-frequency gain and new, deep- fitting CIC instruments may increase the availability of ear canal and pinna-related spectral cues.

The decrease on front/back localization errors following accommodation periods in this study underscores the importance of acclimatization to new hearing aids. Improvement in localization ability over time is not necessarily something that would warrant adjustments to hearing aid settings, but it should be discussed with new hearing aid users with reference to their expectations during the trial period and thereafter.

Though sound source localization is important for speech perception in complex listening environments, it should be noted that the hearing instruments in this study were programmed without directionality. For many hearing aid users, directional microphones will improve the ability to understand primary speech stimuli in front of the listener so binaural and monaural localization cues may be of decreased significance in some circumstances.

References

Arbogast, T.L., Mason, C.R. & Kidd, G. (2002). The effect of spatial separation on informational and energetic masking of speech. Journal of the Acoustical Society of America 112, 2086-2098.

Best, V., Kalluri, S., McLachlan, S., Valentine, S., Edwards, & Carlile, S. (2010). A comparison of CIC and BTE hearing aids for three-dimensional localization of speech. International Journal of Audiology, Early Online, 1-10.

Blauert, J. (1997). Spatial Hearing: The Psychophysics of Human Sound Localization. Cambridge: MIT Press.

Bregman, A. (1990). Auditory Scene Analysis. Cambridge: MIT Press.

Butler, R.A. (1986). The bandwidth effect on monaural and binaural localization. Hearing Research 21, 67-73.

Byrne, D., Noble, W. & LePage, B. (1992). Effects of long-term bilateral and unilateral fitting of different hearing aid types on the ability to locate sounds. Journal of the American Academy of Audiology 3, 369-382.

Byrne, D. &  Noble, W.  (1998).  Optimizing sound localization with hearing aids. Trends in Amplification 3, 51-73.

Freyman, R.L., Balakrishnan, U., & Helfer, K.S. (2001). Spatial release from informational masking in speech recognition. Journal of the Acoustical Society of America 109, 2112-2122.

Hebrank, J., & Wright, D. (1974). Spectral cues used in the localization of sound sources on the median plane. Journal of the Acoustical Society of America 56, 1829-1834.

Jin, C., Best, V., Carlile, S., Baer, T. & Moore, B.C.J. (2002). Speech localization. Proceedings of the Audio Engineering Society 112th Convention. Munich, Germany.

Keidser, G., Rohrseitz, K., Dillon, H., Hamacher, V., Carter, L. et al. (2006). The effect of multi-channel wide dynamic range compression, noise reduction and the directional microphone on horizontal localization performance in hearing aid wearers. International Journal of Audiology 45, 563-579.

Middlebrooks, J.C. (1992). Narrow band sound localization related external ear acoustics. Journal of the Acoustical Society of America  92, 2607-2624.

Moore, B.C., Glasberg, B.R. & Stone, M.A. (1999). Use of a loudness model for hearing aid fitting: III. A general method for deriving initial fittings for hearing aids with multi-channel compression. British Journal of Audiology 33, 241-258.

Noble, W., Byrne, D., & LePage, B. (1994). Effects on sound localization of configuration and type of hearing impairment. Journal of the Acoustical Society of America 95, 992-1005.

Noble, W., Byrne, D., & Ter-Host, K. (1997). Auditory localization, detection of spatial separateness and speech hearing in noise by hearing-impaired listeners. Journal of the Acoustical Society of America 102, 2343-2352.

Rakerd, B., VanderVelde, T.J. & Hartmann, W.M.  (1998). Sound localization in the median sagittal plane by listeners with presbyacusis. Journal of the American Academy of Audiology 9, 466-479.

Van den Bogaert, T., Klasen, T.J., Moonen, M., Van Deun, L. & Wouters, J. (2006). Horizontal localization with bilateral hearing aids: without is better than with. Journal of the Acoustical Society of America 119, 515-526.

Wallach, H. (1940). The role of head movements and vestibular and visual cues in sound localization. Journal of Experimental Psychology 27, 339-368.

Woodworth, .S. (1938). Experimental Psychology. New York: Holt, Rinehart and Winston.

Effects of Digital Noise Reduction on Children’s Speech Understanding

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Effects of Digital Noise Reduction on Speech Perception for Children with Hearing Loss

Stelmachowicz, P., Lewis, D., Hoover, B., Nishi, K., McCreery, R., and Woods, W. (2010)

Because a great deal of everyday communication takes place in the presence of some level of background noise, hearing aid performance in noise is of interest to researchers, clinicians and hearing aid users. It is well established that directional microphones can improve signal-to-noise ratio (SNR) for adult hearing aid users as well as children (Valente et al. 1995; Gravel et al. 1999). It is generally accepted that Digital Noise Reduction (DNR) will not improve speech recognition in noise (Levitt et al. 1993; Bentler et al. 2008). Digital Noise Reduction has, however, resulted in improved overall sound quality judgments and decreased listening effort (Boymans & Dreschler, 2000; Walden et al., 2000; Sarampalis et al., 2009).

In noisy situations, adult listeners use a variety of cues to understand conversational speech, including visual cues, situational cues, semantic and grammatical context. Young children with limited language skills may not be able to take advantage of this information and may rely more on acoustic cues. Indeed, most studies show that children require better SNRs than adults (Blandy & Lutman, 2005; Jamieson et al. 2004).

For hearing-impaired children, hearing aids are more than a tool for the recognition of speech, they facilitate speech and language acquisition and development. As the authors of the current study pointed out, “amplification must facilitate the development of early auditory skills, laying the foundation for the extraction of regularities in the speech signal and the development of language.” Therefore, improving access to speech is of particular importance for young hearing aid users. Conversely, it is also must be determined that DNR or directional processing is not degrading the speech signal.

The purpose of the present study was to determine the effect of DNR on children’s perception of nonsense syllables, words and sentences in the presence of noise. Sixteen children with mild to moderately severe hearing loss participated in the study.  Subjects were divided into two groups: 5-7 year olds and 8-10 year olds. The authors chose these age groups to evaluate the effect of development on the perception of speech stimuli with varying levels of context.  Subjects were fitted with binaural behind-the-ear hearing aids with DNR and amplitude compression. Directional microphones were not activated.  Hearing aids were programmed to DSL 5.0 targets and settings were verified with real-ear measurements.

The children were presented with speech stimuli mixed with speech-shaped noise at SNRs of 0dB, +5dB and +10dB. Three levels of context were represented:

  • VCV (vowel-consonant-vowel) nonsense syllables, 15 consonants combined with /a/
  • Monosyllabic words from the Phonetically Balanced Kindergarten List (PBK – Haskins 1949)
  • Meaningful sentences with three key words each (Bench et al. 1979)

Data analysis revealed that noise reduction did not have a significant positive or negative effect on performance.  There was no significant main effect for context, but not surprisingly, post hoc testing revealed that scores for both age groups were higher for sentences than they were for both nonsense syllables and monosyllables.  Also not surprisingly, performance improved with increases in SNR for all types of speech stimuli. There was a significant effect of age, with older subjects demonstrating better overall performance than younger subjects.  There was no interaction between age and noise reduction, indicating that the use of noise reduction did not affect performance of younger and older subjects differently. There was no interaction between age group and context, indicating that both age groups benefitted from context equivalently.

The authors observed a great deal of variability among subjects, especially the younger group. Though noise reduction did not significantly affect performance overall, the authors found that more than half of the younger subjects demonstrated poorer recognition of words in the DNR-on condition.  The most common consonant confusions were:  /f/ for /t/, /g/ for /d/, and /b/ for /v/, suggesting that voicing information was perceived correctly but place and manner of articulation were not easily distinguished. This finding is in agreement with previous results reported by Jamieson et al (1995) who found that DNR processing resulted in either no improvement or a slight decrement in performance and that consonant place of articulation was particularly affected. Granted, there are several cues that affect consonant perception and slight decrements in the acoustic representation of a consonant may be offset by the availability of other cues. For example, though /f/ and /t/ may be difficult to discriminate, a participant in face to face conversation benefits from visual cues to help identify these consonants. Still, the opportunity exists to further study the effect of noise reduction on consonant perception, with adult and pediatric subjects.

Despite the minimal effect of noise reduction on speech recognition, all listeners in Jamieson’s 1995 study reported a strong preference for DNR processing when hearing continuous speech in a variety of listening environments. This leads to an important consideration regarding the use of noise reduction processing in hearing aids for children. Although the current investigation did not address listening preference, previous studies with adults have often shown positive effects of noise reduction processing on listening effort and sound quality.  The current authors suggested that if this were also the case for children, it could improve attentiveness and increase “time on task” in difficult listening situations. This is an interesting hypothesis, since attention and focus is essential for understanding speech in noise and many hearing-impaired children may demonstrate attention deficits.

Audiologists working with pediatric patients should consider noise reduction settings carefully.  Although there were no statistically significant effects of noise reduction on speech perception in this study, decreases in word recognition scores for younger children in the DNR-on condition is a concern and warrants further study. The authors point out that a child’s ability to recognize and understand speech requires ongoing, consistent auditory experiences. Previous use of amplification, age of identification and consistency of hearing aid use may have influenced the results of this study and may affect success with DNR processing in general.  The effect of degree of hearing loss should also be considered, as it is possible that individuals with severe hearing losses could be adversely affected by even small decrements in speech information resulting from DNR processing.

Clinically, an important highlight of this study is the fact that individual performance among children is highly variable.  Digital Noise Reduction has the potential to ease listening, but may compromise clarity of speech. And directional microphones may improve access to speech, but also risk compromising speech audibility for off-axis talkers.  These considerations suggest that some advanced features should be reserved for older children and specific environments. Among that older population, there may be some inclination to allow manual adjustment of hearing aid settings. However, Ricketts and Galster (2008) correctly point out that children cannot be expected to adjust manual directionality controls reliably. This ultimately results in a fitting rationale that avoids the fitting of some advanced features or allows them to function automatically, with the assumption that they will only be active in the appropriate situations and “do no harm” in regard to speech recognition.

Further study of the perceptual effects of noise reduction and subjective preferences in children is needed. The possibility remains that DNR may offer hearing-impaired children other benefits such as improved attention and comfort in noise, possibly leading to increased satisfaction and compliance from pediatric patients.

References

Bench, J., Kowal, A., & Bamford, J. (1979). The BKB sentence lists for partially-hearing children. British Journal of Audiology 13, 108-112.

Bentler, R., Wu, Y.H., Kettel, J. (2008). Digital noise reduction: Outcomes from laboratory and field studies. International Journal of Audiology 47, 447-460.

Blandy, S. & Lutman, M. (2005). Hearing threshold levels and speech recognition in noise in 7-year-olds. International Journal of Audiology 44, 435-443.

Boymans, M., & Dreschler, W.A. (2000). Field trials using a digital hearing aid with active noise reduction and dual-microphone directionality.  Audiology 39, 260-268.

Gravel, J.S., Fausel, N., Liskow, C. (1999). Children’s speech recognition in noise using omnidirectional and dual microphone hearing aid technology. Ear and Hearing 20, 1-11.

Haskins, H.A. (1949). A phonetically balanced test of speech discrimination for children. Master’s thesis, Northwestern University, Evanston, IL.

Jamieson, D.G., Kranjc, G., Yu, K. (2004). Speech intelligibility of young school-aged children in the presence of real-life classroom noise. Journal of the American Academy of Audiology 15, 508-517.

Levitt, H., Bakke, M., Kates, J. (1993). Signal processing for hearing impairment. Scandanavian Audiology Supplement 38, 7-19.

Ricketts, T.A. & Galster, J. (2008). Head angle and elevation in classroom environments: implications for amplification. Journal of Speech, Language and Hearing Research 15, 516-525.

Sarampalis, A., Kalluri, S., Edwards, B., & Hafter, E. (2009). Objective measures of listening effort: Effects of background noise and noise reduction. Journal of Speech Language and Hearing Research, 52, 1230-1240.

Valente, M., Fabry, D., Potts, L.G. (1995). Recognition of speech in noise with hearing aids using dual microphones. Journal of the American Academy of Audiology 6, 440-449.

Walden, B.E., Surr, R.K., Cord, M.T. (2000). Comparison of benefits provided by different hearing aid technologies. Journal of the American Academy of Audiology 11, 540-560.

Is a patient’s Acceptable Noise Level (ANL) a valid predictor of successful hearing aid use?

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Acceptable Noise Level as a Predictor of Hearing Aid Use

Nabelek, A.K., Freyaldenhoven, M.C., Tampas, J.W., Burchfield, S.B. and Muenchen, R.A. (2006)

This editorial discusses the clinical implications of an independent research study. The original work was not associated with Starkey Laboratories and does not reflect the opinions of the authors.

A common complaint of hearing aid users is difficulty understanding speech in the presence of background noise. This has led to recent interest in examining acceptable noise levels in hearing aid users. Previous research has not shown a correlation between measures of speech perception in noise and successful hearing aid use (Bentler et. al., 1993; Humes et al., 1996), nor have outcome measures generally been useful to predict success with hearing aids (Schum, 1999). The authors of the current study sought to determine if acceptable noise level measurements can be used to predict success with hearing aids.

Acceptable noise level (ANL), is defined as the difference between the most comfortable listening level for running speech and the maximum background noise level that a listener is willing to accept (Nabalek et al., 1991). Therefore, a lower ANL indicates a better tolerance of background noise. Nabelek and her associates compared full-time, part-time and nonusers of hearing aids to examine the relationship between ANL scores, results from the Speech In Noise test (SPIN) scores (Bilger et. al., 1984) and hearing aid use patterns. One of their primary goals was to investigate whether ANL scores could be used clinically to predict future success with hearing aids.

The authors recruited 191 subjects with sensorineural hearing loss whose audiometric thresholds, on average, had a mild-sloping-to-severe configuration. All subjects were binaural hearing aid users, having been fitted between three months and three years prior to testing. Subjects were fitted by a variety of audiologists who were independent of the study, so the hearing aid models, features and signal processing strategies differed among the subjects.

ANL scores and SPIN scores were obtained with speech and noise presented through the same speaker at a 0° azimuth angle. Following sound field testing, subjects responded to a brief questionnaire, which assigned them to one of three groups of hearing aid users: full-time, part-time and non-users. Full time users were defined as those who wore their hearing aids whenever they needed them, part-time users wore their hearing aids occasionally, and non-users had completely stopped wearing their hearing aids.

The first 58 subjects were tested in three sessions over the first three months of acclimatization with hearing aids. These subjects showed consistent ANL and SPIN scores over the three sessions, so the authors concluded that acclimatization to new hearing aids did not affect test results and remaining subjects were tested in one session only.

The authors found that SPIN and ANL scores were generally not affected by age, gender or pure tone average. SPIN scores were significantly better in the aided condition for all listener groups, regardless of hearing aid use pattern. ANL scores were not significantly different between aided and unaided conditions, but unaided and aided ANLs were strongly correlated to hours of hearing aid use and overall hearing aid use pattern. Full-time hearing aid users demonstrated significantly lower ANL scores than part time users, who in turn demonstrated lower ANL scores than non-hearing aid users.  SPIN scores and ANL scores were not strongly correlated. The authors underscored the difference between SPIN and ANL scores, in that SPIN scores indicated the benefit of amplification for speech perception, whereas the ANL scores indicated the difference between successful and unsuccessful hearing aid users. This interpretation of the ANL  results was supported by regression analyses that suggest the ANL predicted successful hearing aid outcome with 87% accuracy and unsuccessful hearing aid outcome with 83.6% accuracy. Listeners with ANLs of 5 or below were expected to be successful users and those with ANLs of 15 or higher were expected to be unsuccessful.

Some results of this study should be interpreted with caution for a number of reasons. First, the subjects in the study were all experienced hearing aid users–defined as no more than three years of prior hearing aid use. The authors acknowledged that to truly determine predictive value, unaided testing should be conducted prior to hearing aid fitting, but did not specify that it should be done prior to a first time hearing aid fitting. Therefore, results obtained in the current study inherently represent previous experience with amplification and previously established hearing aid use patterns.

Second, the authors defined full-time hearing aid users as those subjects who used their hearing aids “whenever they needed them”. Many audiologists would question whether this use pattern should truly be considered “full time”. Indeed, clinical experience indicates that patients who use their hearing aids most of the day, every day, are the most successful and comfortable with their hearing aids. Most practicing audiologists would consider patients who use their hearing aids “as needed” to be part-time users, unless “as needed” was defined as a significant portion of every day.

Third, the subjects in this study were fitted by their own audiologists in independent clinics, and more importantly, used a wide variety of hearing instruments with different features and signal processing characteristics. Therefore, their responses to background noise likely varied with signal processing features that were not controlled variables in this study.

Additional work, with strict controls, should be considered in order to truly investigate the predictive value of the ANL test. Future studies should evaluate new hearing aid users prior to their initial fitting in the unaided condition, then conduct subsequent aided testing periodically during an acclimatization period. Under those circumstances, the unaided ANL could not represent longitudinal effects that have already occurred in response to regular hearing aid use. While Nabelek and colleagues (2004) found that there was no change in ANL or SPIN scores for hearing aid users over the first three months of acclimatization. The participant’s  previous experience with hearing aids was not controlled; approximately half of the subjects were new users and half had experience with hearing aids. Other studies have shown (Keidser et al., 2008) that acclimatization to hearing aids can extend long beyond the first three months and may continue even beyond one year of use, so the subjective judgments of experienced users could be different from those of inexperienced hearing aid users, even those tested after a few months of use. For this reason, longitudinal study of acceptable noise levels in hearing aid users may be of interest.

One may caution against the use of the  ANL as an absolute predictive measure of success with hearing aids. The goal of the clinical audiologist is to rehabilitate hearing impaired individuals, which usually includes fitting them with appropriate hearing aids, counseling and training. If patients who demonstrate high ANL scores are not expected to be successful with hearing aids; should it follow that these patients be discouraged from trying hearing aids? The authors comment that these patients should be counseled about the “limitations of hearing aids even in quiet listening situations”. This conclusion could be detrimental to patient care if hearing aid use is ruled out before the patient is even given a chance to have a trial with them. Regarding subjects with moderate ANL scores, the authors rightly point out the importance of directional microphones and noise reduction, both of which can significantly improve measured ANLs (Pisa et al, 2010). However, these features can be beneficial to all hearing aid users to some degree and would therefore be discussed and recommended regardless of ANL outcome.  Perhaps a moderate to high ANL score could indicate a need for more aggressive noise reduction at the initial fitting. This is, however, speculation as no work has been published evaluating the effect of changing noise reduction parameters on ANL scores.

The authors considered their analyses to be an indication that ANL score can predict future success, or at least consistency of use, with hearing aids. However, all of their subjects had previous experience with hearing aids and many had previously established use patterns. Correlation does not implicitly suggest causation; in that regard it should be considered that subjects’ use patterns were predictive of their ANL scores, rather than vice versa.  Studies of auditory plasticity have shown that auditory experiences, including use of amplification, can affect objective performance and subjective assessments beyond 12 months after the initial fitting (Palmer et. al., 1998; Keidser et al, 2008).  Therefore, it follows that the subjective acceptance of background noise, as measured by the ANL, can differ between new and experienced users and that changes within the auditory system could result in improved noise tolerance.

Perhaps the most important insight to be gained from the current study is the importance of consistent hearing aid use. The authors found that consistent pattern of use of hearing aids was highly correlated to low ANL scores. Rather than supporting the clinical use of ANL scores as a predictive tool, these results may instead indicate that consistent hearing aid users have adjusted to amplified sound and have learned to parse complex acoustic information so that they are better able to withstand increasing background noise levels.  All hearing aid patients should be counseled about the importance of consistent use, not only to determine the need for future programming modifications, but also to aid their process of acclimatization to amplified sound, including their acceptance of background noise.

References:

Bentler, R.A., Niebuhr, J.P., Getta, C.V. & Anderson, C.V. (1993). Longitudinal study of hearing aid effectiveness II: subjective measures. Journal of Speech and Hearing Research 36: 820-831.

Bilger, R.C., Neutzel, J.M., Rabinowitz, W.M. & Rzeczkowski, C. (1984). Standardization of a test of speech perception in noise. Journal of Speech and Hearing Research 27: 32-48.

Humes, .L.E., Halling, D., & Coughlin, M. (1996). Reliability and stability of various hearing aid outcome measures in a group of elderly hearing aid wearers. Journal of Speech, Language and Hearing Research 39: 923-935.

Keidser, G., O’Brien, A., Carter, L., McLelland, M. & Yeend, I.(2008). Variation in preferred gain with experience for hearing-aid users. International Journal of Audiology, 47:10, 621-635

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.

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., 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.

Palmer, C.V., Nelson, C.T. & Lindley, G.A. (1998). The functionally and physiologically plastic adult auditory system. Journal of the Acoustical Society of America, 103, 1705-1721.

Schum, D.J. (1999). Perceived hearing aid benefit in relation to perceived needs. Journal of the American Academy of Audiology 10: 40-45.

A comparison of Receiver-In-Canal (RIC) and Receiver-In-The-Aid (RITA) hearing aids

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Article of interest:

The Effects of Receiver Placement on Probe Microphone, Performance and Subjective Measures with Open Canal Hearing Instruments

Alworth, L., Plyler, P., Bertges-Reber, M. & Johnstone, P. (2010)

This editorial discusses the clinical implications of an independent research study. The original work was not associated with Starkey Laboratories and does not reflect the opinions of the authors.

Open-fit behind-the-ear hearing instruments are favored by audiologists and patients alike, because of their small size and discreet appearance, as well as their ability to minimize occlusion. The performance of open-fit instruments with the Receiver-In-The-Aid (RITA) and Receiver-In-Canal (RIC) has been compared to unaided conditions and to traditional, custom-molded instruments. However, few studies have examined the effect of receiver location on performance by comparing RITA and RIC instruments to each other. In the current paper, Alworth and her associates were interested in the effect of receiver location on:

- occlusion

- maximum gain before feedback

- speech perception in quiet and noise

- subjective performance and listener preferences

Theoretically, RIC instruments should outperform RITA instruments for a number of reasons. Delivery of sound through the thin tube on a RITA instrument can cause peaks in the frequency response, resulting in upward spread of masking (Hoen & Fabry, 2007). Such masking effects are of particular concern for typical open-fit hearing aid users; individuals with high-frequency hearing loss. RIC instruments are also capable of a broader bandwidth than RITA aids (Kuk & Baekgaard, 2008) and may present lowered feedback risk because of the distance between the microphone and receiver (Ross & Cirmo, 1980), and increased maximum gain before feedback (Hoen & Fabry, 2007; Hallenbeck & Groth, 2008).

The authors recruited twenty-five subjects with mild to moderate, high frequency, sensorineural hearing loss participated in the study. Fifteen had no prior experience with open-canal hearing instruments, whereas 10 had some prior experience. Each subject was fitted bilaterally with RIC and RITA instruments with identical signal processing characteristics, programmed to match NAL-NAL1 targets. Directional microphones and digital noise reduction features were deactivated. Subjects used one instrument type (RIC or RITA) for six weeks before testing and then wore the other type for six weeks before being tested again. The instrument style was counterbalanced among the subjects.

Probe microphone measures were conducted to evaluate occlusion and maximum gain before feedback. Speech perception was evaluated with the Connected Speech Test -CST (Cox et al, 1987), the Hearing in Noise test -HINT (Nilsson, et al, 1994), the High Frequency Word List – HFWL (Pascoe, 1975) and the Acceptable Noise Level – ANL test (Nabelek et al, 2004). Subjective responses were evaluated with the Abbreviated Profile of Hearing Aid Benefit – APHAB (Cox & Alexander, 1995), overall listener preferences for quiet and noise, and satisfaction ratings for five criteria: sound quality, appearance, retention and comfort, speech clarity and ease of use and care.

Real-Ear Occluded Response measurements showed minimal occlusion for both types of instruments in this study. Although there was more occlusion overall for RIC instruments, the difference between RIC and RITA hearing instruments was not significant. Overall maximum gain before feedback did not differ between RIC and RITA instruments. However, when analyzed by frequency, the authors found significantly greater maximum gain in the 4000-6000Hz range for RIC hearing instruments.

On the four speech tests, there were no significant differences between RITA versus RIC instruments. Furthermore, there were no significant improvements for aided listening over unaided, except for experienced users with RIC instruments on the Connected Speech Test (CST). It appears that amplification did not significantly improve scores in quiet conditions, for either instrument type, because of ceiling effects. The high unaided speech scores indicated that the subjects in this study, because of their audiometric configurations, already had broad enough access to high frequency speech cues, even in the unaided conditions. Aided performance in noise was significantly poorer than unaided on the HINT test, but no other significant differences were found for aided versus unaided conditions. This finding was in agreement with previous studies that also found degraded HINT scores for aided versus unaided conditions (Klemp & Dhar, 2008; Valente & Mispagel, 2008).

APHAB responses indicated better aided performance for both instrument types than for unaided conditions on all APHAB categories except aversiveness, in which aided performance was worse than unaided. There were no significant differences between RIC and RITA instruments. However, satisfaction ratings were significantly higher for RIC hearing instruments. New users reported more satisfaction with the appearance of RIC instruments; experienced users indicated more satisfaction with appearance, retention, comfort and speech clarity. Overall listener preferences were similar, with 80% of experienced users and 74% of new users preferring RIC instruments over RITA instruments.

The findings of Alworth and colleages are useful information for clinicians and their open-fit hearing aid candidates. Because they provided significantly more high frequency gain before feedback than RITA instruments, RIC instruments may be more appropriate for patients with significant high-frequency hearing loss. Indeed, this result may suggest that RIC instruments should be the preferred recommendation for open-fit candidates. The results of this study also underscore the importance of using subjective measures with hearing aid patients. Objective speech discrimination testing did not yield significant performance differences between RIC and RITA instruments, but participants showed significant preference for RIC instruments.

Further information is needed to compare performance in noise with RIC and RITA instruments. In this study and others, some objective scores and subjective ratings were poorer for aided conditions than unaided conditions. It is important to note that in the current study, all noise and speech was presented at a 0° azimuth angle, with directional microphones disabled. In real-life environments, it is likely that users would have directional microphones and would participate in conversations with various noise sources surrounding them. Previous work has shown significant improvements with directionality in open-fit instruments (Valente & Mispagel, 2008; Klemp & Dhar, 2008). Future work comparing directional RIC and RITA instruments, in a variety of listening environments, would be helpful for clinical decision making.

Although the performance effects and preference ratings reported here support recommendation of RIC instruments clinicians should still consider other factors when discussing options with individual patients. For instance, small ear canals may preclude the use of RIC instruments because of retention, comfort or occlusion concerns. Patients with excessive cerumen may prefer RITA instruments because of easier maintenance and care, or those with cosmetic concerns may prefer the smaller size of RIC instruments. Every patient’s individual characteristics and concerns must be considered, but the potential benefits of RIC instruments warrant further examination and may indicate that this receiver configuration should be recommended over slim-tube fittings.

References

Alworth, L.N., Plyler, P.N., Rebert, M.N., & Johstone, P.M. (2010). The effects of receiver placement on probe microphone, performance, and subjective measrues with open canal hearing instruments. Journal of the American Academy of Audiology, 21, 249-266.

Cox, R.M., & Alexander, G.C. (1995). The Abbreviated Profile of Hearing Aid Benefit. Ear and Hearing, 16, 176-186.

Cox, R.M., Alexander, G.C. & Gilmore, C. (1987). Development of the Connected Speech Test (CST). Ear and Hearing, 8, 119-126.

Hallenbeck, S.A., & Groth, J. (2008). Thin-tube and receiver-in-canal devices: there is positive feedback on both! Hearing Journal, 61(1), 28-34.

Hoen, M. & Fabry, D. (2007). Hearing aids with external receivers: can they offer power and cosmetics? Hearing Journal, 60(1), 28-34.

Klemp, E.J. & Dhar, S. (2008). Speech perception in noise using directional microphones in open-canal hearing aids. Journal of the American Academy of Audiology, 19(7), 571-578.

Kuk, F. & Baekgaard, L. (2008). Hearing aid selection and BTEs: choosing among various “open ear” and “receiver in canal” options. Hearing Review, 15(3), 22-36.

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

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

Pascoe, D. (1975). Frequency responses of hearing aids and their effects on the speech perception of hearing impaired subjects. Annals of Otology, Rhinology and Laryngology suppl. 23, 84: #5, part 2.

Valente, M. & Mispagel, K. (2008). Unaided and aided performance with a directional open-fit hearing aid. International Journal of Audiology, 47, 329-336.

Does listening experience affect a hearing aid wearer’s preferred gain?

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Article of interest:

Variation in Preferred Gain with Experience for Hearing-Aid Users

Keidser, G., O’Brien, A., Carter, L., McLelland, M., and Yeend, I. (2008)

 

This editorial discusses the clinical implications of an independent research study. The original work was not associated with Starkey Laboratories and does not reflect the opinions of the authors.

Auditory plasticity, or the reorganization of neural connections in the auditory system, has been documented in studies with human and animal subjects (Palmer et. al., 1998; Philibert et. al, 2005; Willott, 1996). These studies found that the representation of acoustic stimuli along auditory pathways can change based on auditory experience. The concept of auditory plasticity may relate to hearing aid patients in two ways: first, neural reorganization is likely to occur in response to the hearing loss itself, then subsequent reorganization may occur in response to amplification. Indeed, most clinicians observe that new hearing aid users experience an adjustment period in which they prefer less gain, but that over time they are able to accept increases in gain.

The clinical manifestation of auditory plasticity is sometimes associated with acclimatization to amplification and has been studied in hearing aid users in numerous ways: preferred gain for new and experienced users (Marriage, et al., 2004; Cox and Alexander, 1992; Horwitz & Turner, 1997), speech performance over time (Bentler, et al.1993a, Gatehouse, 1992), subjective benefit or sound quality over time (Bentler, et al., 1993b; Ovegard, et al., 1997), loudness perception and intensity discrimination over time (Olsen, et al., 1999; Philibert et al., 2002), even changes in ABR wave V latency (Philibert, et al, 2005). Most studies have found small but significant changes over time as participants adjusted to amplified sound. Others, however, have found no significant difference between new and experienced hearing aid users (Smeds et al, 2006a, 2006b). Some recent work suggests that acclimatization may occur specifically in relation to high level, high frequency sounds (Munro & Lutman, 2003).

The authors of the current study were specifically interested in comparing gain preferences and loudness perception in new hearing aid users and users with more than 3 years of experience with hearing aids. Fifty new users and twenty-six experienced users, most with mild to moderate sensorineural hearing loss, were fitted with digital, two-channel, WDRC instruments equipped with volume controls. Compression attack and release characteristics were set identically for all subjects and a noise reduction algorithm was turned off. The hearing aids had three independent programs:

  1. NAL-NL1 target response
  2. NAL-NL1 with a 6dB high-frequency cut at 3000Hz (HFC)
  3. NAL-NL1 with a 6dB low-frequency cut at 500Hz (LFC)

Subjects were asked to compare the programs in everyday environments and record their preferred overall program. Follow-up testing was conducted at 1 month, 4 months and 13 months post-fitting and subjects were specifically instructed to arrive at each appointment with the device on their overall preferred program and volume control setting. At each appointment, 2-cc coupler and real-ear measurements were obtained with hearing instruments at the preferred settings. Questionnaires were administered to record hearing aid usage time, ranking and performance of the three programs and to what extent the volume control was used. Loudness perception tests were performed using a categorical loudness scale test (Cox & Alexander, 1997) to determine the median SPL levels that were categorized as “comfortable”.

The authors found that new and experienced users preferred the high-frequency cut (HFC) program most often. Initially, about 60% of the new users preferred the HFC program, but by 13 months post-fitting the preferences of new and experienced users were very similar with approximately half of the subjects still preferring the HFC program. Fewer than 10% of the users preferred the LFC program across the duration of the study.

On average, overall preferred gain was 3dB lower for new users and increases were noted at subsequent appointments. By the time of the final appointment, new users reported higher gain settings than they did before, but did not reach the preferred levels of experienced users. This suggests that the gain acclimatization process for some users may continue beyond the 13-month point. Degree of hearing loss had a significant effect, as subjects with moderate hearing loss preferred 6dB lower overall gain than those with mild hearing loss.

The findings of Keidser and colleagues offer important implications for clinical practice. First, it appears that new hearing aid users experience acclimatization with regard to comfortable loudness and preferred gain settings. This supports the use of adaptation levels in hearing aid software, though some adaptation managers may provide larger decrements in overall gain (5-10dB) than many hearing aid users require. The fact that new users with mild hearing loss did not prefer as much initial gain reduction as those with moderate losses indicates that audiometric thresholds should be considered. The authors noted that more information is needed about acclimatization effects in new hearing aid users with more than moderate hearing loss. However, it is probably appropriate for clinicians to assume that for patients with moderate to severe hearing loss, lower initial gain settings may be needed and an extended period of adjustment may be expected.

Recent emphasis on evidence-based clinical practice underscores the importance of verification measures to ensure adequate gain and frequency response from new hearing aids. However, study of auditory acclimatization demonstrates that it is equally important to evaluate the patient’s perception of the amplified sound to ensure satisfaction. Ultimately, a patient with excellent aided test results may still reject new hearing aids if they are not comfortable.

Hearing aid acclimatization can be measured several ways, many of which are not viable for busy clinical practices. But there are two simple ways in which it should be addressed during the hearing aid fitting and follow-up appointments. At the fitting appointment, patients should be counseled about appropriate expectations for the adjustment process. For instance, patients who know ahead of time that it is normal to notice, and perhaps be slightly annoyed by, newly amplified sounds are less likely to be disheartened when this occurs. They should be advised to wear their hearing aids as consistently as possible and to report any discomfort or pain so it can be addressed with programming adjustments.

Initially, high frequency gain in particular may need to be reduced relative to target settings. However, care should be taken to determine each individual’s comfort with high frequency sounds. In the current study, individuals were free to reduce high frequency gain at any time by selecting the HFC program. It seems appropriate to question whether this affected their ability to adjust to high-frequency gain and if they would have eventually been able to tolerate, even prefer, more high-frequency amplification had they not been able to switch at will into the HFC program. The importance of high-frequency information for speech intelligibility, especially in noise, is well established (Turner & Henry, 2002; Hornsby & Ricketts, 2003). To avoid detrimental effects on speech perception, high frequency gain should approach targets as closely as possible, while still maintaining patient comfort.

At follow-up appointments, patients should be questioned in detail about their comfort and overall progress with the new aids. Formal questionnaires like the APHAB (Cox and Alexander, 1995) can be used to determine specific sound preferences so that appropriate adjustments can be made. The more precise information a clinician obtains from a patient, the more likely they are to zero in on necessary programming changes. One important point to note is that this study evaluated gain preferences only. Most hearing instruments have several adjustable parameters, and some new users might respond as favorably to increased compression ratios or lowered compression kneepoints, thereby reducing louder sounds but maintaining gain for low to moderate level sounds.

Because it appears that the acclimatization process may continue beyond a year, follow-up care after the initial trial period should be planned accordingly. It may be appropriate to schedule check-ups at 4-months, 8-months and 12-months post-fitting. This way, final target settings can be approached systematically for each individual.

References

Bentler, R.A., Niebuhr, D.P., Getta, J.P. & Anderson, C.V. 1993a. Longitudinal study of hearing aid effectiveness. I. Objective measures. Journal of Speech and Hearing Research 36, 808-819.

Bentler, R.A., Niebuhr, D.P., Getta, J.P. & Anderson, C.V. 1993b. Longitudinal study of hearing aid effectiveness. II. Subjective measures. Journal of Speech and Hearing Research 36, 820-831.

Cox, R.M. & Alexander, G.C. 1992. Maturation of hearing aid benefit: Objective and subjective measurements. Ear and Hearing, 13, 131-141.

Cox, R.M. & Alexander, G.C. 1995. The Abbreviated Profile of Hearing Aid Benefit (APHAB). Ear and Hearing, 16, 176- 186.

Cox, R.M., Alexander, G.C., Taylor, I.M. & Gray, G.A. 1997. The contour test of loudness perception. Ear and Hearing, 18, 388-400.

Gatehouse, S. 1992. The time course and magnitude of perceptual acclimatization to frequency responses: Evidence from monaural fitting of hearing aids. Journal of the Acoustical Society of America 92, 1258-1268.

Hornsby, B.W. & Ricketts, T.A. 2003. The effects of hearing loss on the contribution of high- and low-frequency speech information to speech understanding. Journal of the Acoustical Society of America, 113(3), 1706-1717.

Horwitz, A.R. & Turner, C.W. 1997. The time course of hearing aid benefit. Ear and Hearing, 18, 1-11.

Keidser, G., Dillon, H., & Byrne, D. 1998. The change in overall level, spectral shape and loudness perception of speech produced with different vocal effort. Australian Journal of Audiology, 44, 656-670.

Keidser, G., O’Brien, A., Carter, L., McLelland, M., & Yeend, I. (2008). Variation in preferred gain with experience for hearing aid users. International Journal of Audiology, 47, 621-635.

Marriage, J., Moore, B.C. & Alcantara, J.I. 2004. comparison of three procedures for initial fitting of compression hearing aids. III. Inexperienced versus experienced users. International Journal of Audiology, 43, 198-210.

Munro, K.J. & Lutman, M.E. 2003. The effect of speech presentation level on measurement of auditory acclimatization to amplified speech. Journal of the Acoustical Society of America, 114, 484-495.

Olsen, S.O., Rasmussen, A.N., Nielsen, L.H. & Borgkvist, B.V. 1999. Loudness perception is influenced by long-term hearing aid use. Audiology, 38, 202-205.

Ovegard, A., Lundberg, G., Hagerman, B., Gabrielsson, A., Bengtsson, M. 1997. Sound quality judgment during acclimatization of hearing aid. Scandanavian Audiology, 26, 43-51.

Palmer, C.V., Nelson, C.T. & Lindley, G.A. 1998. The functionally and physiologically plastic adult auditory system. Journal of the Acoustical Society of America, 103, 1705-1721.

Philibert, B., Collet, L., Vesson, J.F. & Veuillet, E. 2002. Intensity-related performances are modified by long-term hearing aid use: A functional plasticity? Hearing Research, 165, 142-151.

Philibert, B., Collet, L., Vesson, J.F. & Veuillet, E. 2005. The auditory acclimatization effect in sensorineural hearing-impaired listeners: Evidence for functional plasticity. Hearing Research, 205, 131-142.

Smeds, K., Keidser, G., Zakis, J., Dillon, H., Leijon, A. 2006a. Preferred overall loudness. I. Sound field presentation in the laboratory. International Journal of Audiology, 45, 12-25.

Smeds, K., Keidser, G., Zakis, J., Dillon, H., Leijon, A. 2006b. Preferred overall loudness. II. Listening through hearing aids in field and laboratory tests. International Journal of Audiology, 45, 12-25.

Turner, C.W. & Henry, B.A. 2002. Benefits of amplification for speech recognition in background noise. Journal of the Acoustical Society of America, 112, 1675-1680.

Willott, J.F. 1996. Physiological plasticity in the auditory system and its possible relevance to hearing aid use, deprivation effects, and acclimatization. Ear and Hearing, 17, 66S-77S.

Do over-the-counter hearing aids offer a quality solution to better hearing?

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Article of interest:

An Electroacoustic Analysis of Over-the-Counter Hearing Aids
Callaway, S.L., and Punch, J.L. (2008)

This editorial discusses the clinical implications of an independent research study. The original work was not associated with Starkey Laboratories and does not reflect the opinions of the authors.

Hearing-impaired individuals have a variety of amplification options available to them. Audiologists help patients select the most appropriate hearing aids based on their hearing loss, lifestyle and listening needs, manual dexterity and a number of other factors.  Financial constraints are often a consideration as well, so hearing aid manufacturers offer a wide selection of circuit types, including some more basic, economical choices.

In today’s economy, consumers seem more concerned than ever about hearing aid cost. Not surprisingly, there has been an increase in the availability of inexpensive, over-the-counter (OTC) hearing devices. The price of an OTC instrument can range from under $50 to several hundred dollars each. While some of these devices might fit the FDA definition of “hearing aids” (FDA, 2007a; S874.3300), their distribution often does not meet FDA requirements. For instance, the FDA requires a person buying a hearing aid to be examined by a physician to rule out medical contraindications and a medical waiver must be signed if they choose not to obtain medical clearance. Most OTC devices are purchased in a retail store or over the internet, so the consumer never interacts with an audiologist and may never be asked for proof of medical clearance. Indeed, the authors of the current study found only one OTC manufacturer that asked consumers to sign a medical waiver prior to purchase.

Despite the decidedly non-clinical distribution of most OTC hearing devices, many audiologists have encountered them, either through advertising or via a patient who has purchased one before coming to our office. Because we recognize the importance of proper diagnosis, selection, fitting verification and follow-up care, most audiologists have significant reservations about the safety and quality of OTC devices.

These concerns appear to be well founded. The current authors found only one OTC manufacturer that required consumers to submit an audiogram or select an audiometric profile when purchasing an instrument. When they contacted customer service for several OTC manufacturers, they found that representatives had very little knowledge of the technical characteristics of their devices and were unwilling or unable to provide instrument specifications. Previous research has shown that some OTC devices over-amplify in the low frequencies and that only reverse-slope hearing losses could be suitably fitted (Cheng & McPherson, 2000).

There is a need for more information about the performance of OTC hearing devices so that audiologists can counsel patients about potential benefits and limitations. In the current study, Callaway and Punch examined electroacoustic characteristics of eleven OTC hearing devices. The selected OTC instruments were categorized into two groups: low-cost devices priced from $10 to $73 and mid-range devices priced from $349 to $495. The low-cost devices were behind-the-ear, receiver-in-canal style or in-the-canal style. The mid-range devices were in-the-ear or in-the-canal styles.

Technical specification sheets were obtained from the manufacturers of the mid-range devices, but the authors found that specifications for low-cost devices were either unreliable or unavailable. Therefore, they purchased all of the low-cost devices and conducted their own electroacoustic measurements (ANSI 1987, 1996). Tests were conducted twice, two months apart, to ensure reliability and validity of the data. Two of the low-range devices were excluded because they were not working at the time of the second round of testing.

The authors compared NAL-R prescribed gain and output targets (Byrne & Dillon, 1986; Dillon, 2001) to actual gain and outputs measured from the OTC hearing devices. In order to be deemed acceptable for a particular audiometric configuration, gain was required to be within +/-12dB of the NAL targets and output was required to be between -5dB and +3dB of the target. The frequency range was required to provide measurable gain between 250 to 6000Hz.

Overwhelmingly, Callaway and Punch found that OTC devices had more gain in the low-frequencies than in the high-frequencies. In fact, all of the low-cost devices were classified as “special purpose” devices because of their low-frequency emphasis and as a result had to be tested using lower three-frequency averages. Total harmonic distortion was within tolerance for all but one OTC instrument, but equivalent input noise was often well above ANSI standards. Only two of the devices, both mid-range devices, had acceptable frequency responses from 250-6000Hz. Most frequency responses were peaked rather than smooth, with some peaks as high as 15dB in the range of 1000Hz to 5000Hz.

Gain and output measures yielded variable results across audiometric configurations for low-cost and mid-range OTC instruments  Because so many of the OTC devices over-amplified in the low frequencies, gain targets for the mild-sloping hearing loss configuration were not met, but the flat-moderate hearing loss targets were met more easily.  The moderate-sloping loss was the poorest fit, especially for low-cost instruments, primarily because they were unable to provide adequate gain for high frequencies.

The authors concluded that the low-cost instruments were inadequate for use by hearing-impaired individuals, because of over-amplification in low frequencies, inadequate high-frequency amplification, high input noise, and narrow frequency response. These conclusions are supported by previous research (Killion, 2003). However, the mid-range instruments had gain and output characteristics that were somewhat more like traditional hearing instruments. Therefore, they could potentially be considered an acceptable low-cost solution for consumers who cannot afford traditional hearing aids dispensed by a hearing care professional.  Of course, any of these instruments are more likely to help if consumers are asked to submit recent audiograms or choose an audiometric profile before purchase.

The findings in this study corroborate the concerns many audiologists have about the performance of over-the-counter hearing devices, especially low-cost instruments. In addition to the adverse effects of a reverse-sloping, narrow frequency response, high output levels and frequency response peaks are likely to cause many users of OTC instruments to turn their devices down in order to avoid discomfort or feedback. The resulting reduction in gain would thereby fall even farther below required levels. Because these devices cannot be programmed to an individual’s prescribed settings, most users would likely be forced to choose between inadequate gain or discomfort and feedback.

The cost of many OTC hearing devices is low enough that consumers only take a small financial risk if they choose to purchase. However, individuals in need of hearing assistance, having been disappointed with the performance of OTC aids, might assume that appropriately prescribed hearing instruments, fitted and verified by an audiologist, would be no better.

An additional concern regarding the use of OTC products is the fact that purchasers do not get a thorough diagnostic evaluation, nor do they receive recommendations from a qualified hearing care professional. Consumers who forgo a complete audiogram prior to purchasing a hearing device are not referred for appropriate consultation with a physician if they have medical contraindications to hearing aid use or symptoms that require further diagnostic study.

More information about OTC hearing devices is needed, as well as stricter regulation to define and classify them and enforce their proper distribution. More rigorous guidelines should be established to ensure their safety and performance. However, it is also incumbent upon audiologists as hearing care professionals to educate patients about the importance of prescriptive fitting and follow-up care and to guide them to make appropriate decisions about their amplification needs.  Over-the-counter hearing devices are bound to appeal to cost-conscious hearing-impaired individuals. Audiologists must be familiar with the limitations and potential risks of OTC devices and be prepared to discuss them with patients.

References

American National Standards Institute (1987). Specification of hearing aid characteristics (ANSI S3.22-1987). New York: Author.

American National Standards Institute (1996). Specification of hearing aid characteristics (ANSI S3.22-1966). New York: Author.

Byrne, D. & Dillon, H. (1986). The National Acoustic Laboratories’ (NAL) new procedure for selecting the gain and frequency response of a hearing aid. Ear & Hearing, 7, 257-265.

Callaway, S.L., and Punch, J.L. (2008). An Electroacoustic Analysis of Over-the-Counter Hearing Aids. American Journal of Audiology, 17,14-24.

Cheng, C.M., & McPherson, B. (2000). Over-the-counter hearing aids: Electroacoustic characteristics and possible target client groups. Audiology, 39(2), 110-116.

Dillon, H. (2001). Hearing aids. New York: Thieme.

Killion, M. (2003). Citizen petition to the Food and Drug Administration, August 7, 2003. Petition #2003P-0362. Retrieved from www.fda.gov/ohrms/dockets/dailys/03/aud03/081203/03p-0362-cp00001-vol1.pdf.

McPherson, B., & Wong, E.T.L. (2005). Effectiveness of an affordable hearing aid with elderly persons. Disability and Rehabilitation, 27, 601-609.

Parving, A., Christensen, B., Nielsen, J., & Konradsson, K. (2005). Clinical trial of low-cost, high power compression hearing aid. Audiological Medicine, 3(2), 76-81.

U.S. Food and Drug Administration, (2007a). Subpart D – prosthetic devices. Retrieved May 6, 2007, from www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch. 21:8.0.1.1.23.4.

Reviewing the benefits of open-fit hearing aids

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Article of interest:

Unaided and Aided Performance with a Directional Open-Fit Hearing Aid

Valente, M., and Mispagel, K.M. (2008)

This editorial discusses the clinical implications of an independent research study. The original work was not associated with Starkey Laboratories and does not reflect the opinions of the authors. 

With the continued popularity of directional microphone use in open-fit and receiver-in-canal (RIC) hearing aids, there has been increasing interest in evaluating their performance in noisy environments. A number of studies have investigated the performance of directional, open-fit BTEs in laboratory conditions. (Valente et al., 1995; Ricketts, 2000a; Ricketts, 2000b). Some have evaluated directional microphone performance in real-life or simulated real-life noise environments (Ching et al, 2009). In the current study, the authors compared performance in omnidirectional, directional and unaided conditions using RIC instruments in R-SpaceTM (Revitt et al, 2000) recorded restaurant noise. Their goal was to obtain more externally valid results by using real-life noise in a controlled, laboratory setting.

The R-SpaceTM method involved recordings of real restaurant noise from an 8-microphone, circular array. For the test conditions, these recordings were presented through an 8-speaker, circular array to simulate the conditions in the busy restaurant. One important factor that distinguishes this study from most others is that the subjects listened to speech stimuli in the presence of noise from all directions, including the front. At the time of this study only a few other studies had tested directional microphone performance in the presence of multiple noise sources, including frontal (Ricketts, 2000a; Ricketts, 2001; Bentler et al., 2004).

The authors recruited 26 adults with no prior hearing aid experience for the study. They were fitted with binaural receiver-in-canal (RIC) instruments. The instruments were programmed without noise reduction processing and with independent omnidirectional and directional settings. Subjects were counseled on use and care of the instruments, including proper use of omnidirectional and directional programs. They returned for follow-up adjustments one week after their fitting then used their instruments for four weeks before returning for testing. Subjects were given the opportunity to either purchase the hearing aids after the study at a 50% discount or receive a $200 payment for participation.

Hearing in Noise Test (HINT) (Nilsson et al., 1994) sentence reception thresholds were obtained to evaluate sentence perception in the uncorrelated R-Space noise. The Abbreviated Profile of Hearing Aid Benefit (APHAB) (Cox & Alexander, 1995) was also administered to evaluate perceived benefit from the instruments in the study. Four APHAB subscales were evaluated independently:

- Ease of communication (EC)
- Reverberation (RV)
- Background noise (BN)
- Aversiveness to loud sounds (AV)

The authors found that subjects’ performance in the directional condition was significantly better than both omnidirectional and unaided conditions. The omnidirectional condition was not significantly better than unaided; in fact results were slightly worse than those obtained in the unaided condition.

For the APHAB results, the authors found that on the EC, RV and BV subscales, aided scores were significantly better than unaided scores. Perhaps not surprisingly, the AV score, which evaluates “aversiveness to noise” was worse in the aided conditions. The aided results combined omnidirectional and directional conditions, so it is possible that aversion to noise in omnidirectional conditions was greater than the directional conditions. However, this was not specifically evaluated in the current study.

The authors pointed out that their directional benefit, which on average was 1.7dB, was lower than those found in other studies of open-fit or RIC hearing instruments (Ricketts, 2000b; Ricketts, 2001; Bentler, 2004; Pumford et al., 2000). However, they mention that most of those studies did not use frontal noise sources in their arrays. Frontal noise sources should have obvious detrimental effects on directional microphone performance, so it is likely that the speaker arrangement in the current study affected the measured directional improvement. At the time of this publication one other study had been conducted using the R-SpaceTM restaurant noise (Compton-Conley et al 2004). They found mean directional benefits of 3.6 to 5.8 dB, but their subjects had normal hearing and the hearing aids they used were not an open-fit design and were very different from the ones in the current study..

Clinicians can gain a number of important insights from Valente and Mispagel’s study. First and foremost, directional microphones are likely to provide significant benefits for users of RIC hearing aids. At the time of publication, the authors noted that directional improvement should be studied in order to warrant the extra expense of adding directional microphones to an open-fit hearing aid order. However, most of today’s open-fit and RIC instruments already come standard with directional microphones, many of which are automatically adjustable. So there is no need to justify the use of directional microphones on a cost basis, as they usually add nothing to the hearing aid purchase price.

This study provided more evidence for directional benefit in noise, but further work is needed to determine performance differences between directional and omnidirectional microphones in quiet conditions. Dispensing clinicians should always order instruments that have omnidirectional and directional modes, whether manually or automatically adjustable. This helps ensure that the instruments will perform optimally in most situations. Even instruments with automatically adjustable directional microphones often have push-buttons that allow us to give patients additional programs. For example, a manually accessible, directional program, perhaps with more aggressive noise reduction, offers the user another option for excessively noisy situations.

The current study obtained slightly reduced directional effects compared to other studies that tested subjects in speaker arrays without frontal noise sources. This underscores the importance of counseling patients about proper positioning when using directional settings. In general, patients should understand that they will be better off when they can put as much noise behind them as possible. But, it is also important to ensure that patients have reasonable expectations about directional microphones. They must understand that the directional microphone will help them focus on conversation in front of them, but will not completely remove competing noise behind them. Patients must also understand that omnidirectional settings are likely to offer no improvement in noise and might even be a detriment to speech perception in some noisy environments.

Subjects in Valente and Mispagel’s study were offered the opportunity to purchase their hearing instruments at a 50% discount after the study’s completion. Only 8 of the 26 subjects opted to do so. Of the remaining subjects, 3 reported that the perceived benefit was not enough to justify the purchase, whereas 15 subjects did not report any significant perceived benefit. This leads to another important point about patient counseling.

The subjects in this study, like most candidates for open-fit or RIC instruments, had normal low-frequency hearing. Therefore, they may have had less of a perceived need for hearing aids in the first place. It is important for audiologists to discuss realistic expectations and likely hearing aid benefits with patients in detail at the hearing aid selection appointment, before hearing aids are ordered. Patients who are unmotivated or do not perceive enough need for hearing assistance will ultimately be less likely to perceive significant benefit from their hearing aids. This is particularly true in everyday clinical situations, in which patients are not typically offered a 50% discount and will have to factor financial constraints into their decisions. For most open-fit or RIC candidates, their motivation and perceived handicap will be related to their lifestyle: their social activities, employment situation, hobbies, etc. Because a patient who has a less than satisfying experience with hearing aids may be reluctant to pursue them again in the future, it is critical for the clinician to help them establish realistic goals early on, before hearing aid options are discussed.

References
Bentler, R., Egge, J., Tubbs, J., Dittberner, A., and Flamme, G. (2004). Quantification of directional benefit across different polar response patterns. Journal of the American Academy of Audiology 15(9), 649-659.

Ching, T.C., O’Brien, A., Dillon, H., Chalupper, J., Hartley, L., Hartley, D., Raicevich, G., and Hain, J. (2009). Journal of Speech, Language and Hearing Research 52, 1241-1254.

Compton-Conley, C., Neuman, A., Killion, M., and Levitt, H. (2004). Performance of directional microphones for hearing aids: real world versus simulation. Journal of the American Academy of Audiology 15, 440-455.

Cox, R.M. and Alexander, G.C. (1995). The abbreviated profile of hearing-aid benefit. Ear and Hearing 16, 176-183.

Nilsson, M., Soli, S. and Sullivan, J. (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, 1085-1099.

Pumford, J., Seewald, R,. Scollie, S. and Jenstad, L. (2000). Speech recognition with in-the-ear and behind-the-ear dual microphone hearing instruments. Journal of the American Academy of Audiology 11, 23-35.

Revit, L., Schulein, R., and Julstrom, S. (2002). Toward accurate assessment of real-world hearing aid benefit. Hearing Review 9, 34-38, 51.

Ricketts, T. (2000a). The impact of head angle on monaural and bilateral performance with directional and omnidirectional hearing aids. Ear and Hearing 21, 318-329.

Ricketts, T. (2000b). Impact of noise source configuration on directional hearing aid benefit and performance. Ear and Hearing 21, 194-205.

Ricketts, T., Lindley, G., and Henry, P. (2001). Impact of compression and hearing aid style on directional hearing aid benefit and performance. Ear and Hearing 22, 348-360.

Valente, M., Fabry, D., and Potts, L. (1995). Recognition of speech in noise with hearing aids using a dual microphone. Journal of the American Academy of Audiology 6, 440-449.

Valente, M., & Mispagel, K.M. (2008). Unaided and aided performance with a directional open-fit hearing aid. International Journal of Audiology, 47, 329-336.

What considerations should be made when fitting open-canal directional microphone hearing aids?

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Article of interest:

Speech Perception in Noise Using Directional Microphones in Open-Canal Hearing Aids

Klemp, E.J. and Dhar, S. (2008)

This editorial discusses the clinical implications of an independent research study. The original work was not associated with Starkey Laboratories and does not reflect the opinions of the authors.

One of the most common complaints of hearing aid users is difficulty understanding speech in noisy places. Improvements in hearing aid noise reduction may have helped alleviate this problem somewhat, but the most effective solution has been the use of directional microphones (Bentler, 2005).

Behind-the-ear (BTE) hearing aids equipped with directional microphones have been available since the early 1970′s. By the mid 1990′s, the availability of directional microphones in custom hearing aids gave audiologists the opportunity to offer this benefit to patients who preferred in-the-ear (ITE) styles. In recent years, because of their discreet, unobtrusive appearance and comfortable, lightweight fit, open-canal BTEs have become increasingly popular. Most open-canal instruments on the market today have either automatic or manually accessible directional microphone programs.

Research with traditional ITE and BTE instruments has shown that the larger the air vent diameter, the more low-frequency sounds are attenuated (Lybarger, 1985). Therefore, enlarged venting has long been a successful method of reducing perceived occlusion for hearing aid users.  Because the design of open fit hearing aids allows for significantly increased venting, the inherent low-frequency attenuation makes them an excellent option for patients with normal hearing in the low to mid-frequency range and reduces the likelihood of occlusion.

However effective increasing vent diameter may be for reducing occlusion, it has also been demonstrated that the advantage from a directional microphone system is inversely related to vent diameter in traditional hearing aids (Ricketts, 2000). In other words, as the vent diameter increases, the directional effect decreases. The potential reduction in directional benefit, coupled with the possibility of noise entering the open ear canal raises questions about the performance of open-fit hearing aids in noisy situations. The purpose of Kemp and Dhar’s 2008 study was to compare directional hearing aid performance in noise to omnidirectional and unaided conditions.

Sixteen adult subjects with sloping high-frequency hearing losses were tested using the Hearing in Noise Test (HINT) (Nilsson et. al., 1994). The HINT sentences were presented at 65dB in the presence of three channels of competing speech-weighted noise.  Because the authors intended to evaluate hearing aid performance with active noise reduction, the noise was presented with a 12-second lead-in to allow hearing aid signal-processing to become fully activated before the sentences began.

Subjects were fitted with open-fit hearing aids and were evaluated in five counter-balanced conditions:

  • Unaided
  • Omnidirectional mode, no digital noise reduction (OMNI)
  • Omnidirectional mode with digital noise reduction (DNR)
  • Directional mode, no digital noise reduction (DIR)
  • Directional mode with digital noise reduction (BOTH)

The analysis of HINT thresholds (in terms of performance and benefit) in these conditions yielded a number of interesting findings, including:

  1. Directionality alone and combined with digital noise reduction improved thresholds as compared to omnidirectional (by 3.32dB) or unaided (by 2.26 dB) conditions.
  2. Digital noise reduction alone did not improve thresholds.
  3. Omnidirectional conditions (with or without noise reduction) yielded poorer thresholds than unaided conditions.

Though the authors pointed out that the directional benefit found with open-fit BTEs in this study is smaller compared to previous findings with traditional occluded fittings (Nordrum et al, 2006), there was still significant improvement with the use of directional microphones over unaided and omnidirectional conditions. However, they did not find significant improvement with the use of digital noise reduction only and in some DNR-only trials performance was worse than with omnidirectional amplification alone. These findings support the recommendation and use of directional microphones in open-fit hearing aids. Furthermore, they underscore the importance of combining digital noise reduction processing with directionality rather than relying on noise reduction alone to improve speech perception in noise.

Perhaps the most interesting finding, however, is the decrement in performance that the authors found in the omnidirectional conditions. As audiologists, our goal is to help patients function better in everyday situations, so we obviously want to avoid recommendations that could result in increased difficulty. Most open-fit BTEs available today have either automatic or manually adjustable directional programs, so it is possible for patients to be in omnidirectional modes in noisy places unless they are counseled thoroughly on the appropriate use of their programs.

Typical candidates for open-fit hearing aids have normal hearing in the low to middle frequency range. The hearing aids are not providing low-frequency amplification and are therefore not providing a directional advantage in the low-frequency range. High-frequency directionality has been enhanced in recent hearing instruments by reduction in microphone port spacing (Fabry, 2006). This, along with other signal processing advances to extend high-frequency response are likely to result in even better performance in noise with open-fit BTE instruments.

As is often the case in our profession, a patient’s ultimate success and satisfaction with their open-fit hearing aids may depend on adequate counseling on the use of omnidirectional and directional programs. Even patients who prefer to use automatic programs might benefit from having an additional, manually-accessible directional program, for use in situations when the automatic program does not adequately reduce competing noise.  Either way, patients need to understand directionality and how their hearing aids are likely to respond to noise backgrounds in everyday conditions so that they can position themselves appropriately and adjust their aids to the proper setting.

References

Bentler, R. (2005) Effectiveness of directional microphones and noise reduction schemes in hearing aids: a systematic review of the evidence. Journal of the American Academy of Audiology 16: 473-484.

Fabry, D. (2006) Facts vs. myths: the “skinny” on slim-tube open fittings: separating truth from fiction in open fittings. Hearing Review, May. http://www.hearingreview.com /issues/articles/ 2006-05_04.asp

Klemp, E.J., & Dhar, S. (2008). Speech perception in noise using directional microphones in open-canal hearing aids. Journal of the American Academy of Audiology, 19, 571-578.

Lybarger, S. (1985) Earmolds. In: Katz, J. ed. Handbook of Clinical Audiology. 3rd edition. Baltimore: Williams and Wilkins, 885-910.

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.

Nordrum, S., Erler, S., Garstecki, D., Dhar, S. (2006) Comparison of performance on the hearing in noise test using directional microphones and digital noise reduction algorithms. American Journal of Audiology15: 81-91.

Ricketts, T. (2000) Directivity quantification in hearing aids: fitting and measurement effects. Ear and Hearing 21: 45-58.

 

The real-world benefits of directional microphones with infants and young children

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This editorial reviews the published article:

Directional Effects on Infants and Young Children in Real Life: Implications for Amplification
Ching, O’Brien, Dillon, Chalupper, Hartley, Hartley, Raicevich and Hain, 2009

This editorial discusses the clinical implications of an independent research study. The original work was not associated with Starkey Laboratories and does not reflect the opinions of the authors.

The beneficial effect of directional microphone use on adult speech perception in noisy environments is well known and is based on the fact that conversational speech usually takes place with participants facing each other. Reducing the level of competing sound behind the listener, even slightly, can increase the signal-to-noise ratio (SNR), resulting in improved identification and discrimination of speech sounds. Clinical audiologists are accustomed to counseling patients to maintain face-to-face contact whenever possible to get the most benefit from the directional microphones and to take advantage of visual cues as well.

The potential advantage of directional microphone use for children is less understood, partly because children may not employ face-to-face communication as regularly as adults do. Several studies have demonstrated the importance of improved SNR for speech reception in children and it is generally accepted that even children with normal hearing require a greater SNR than adults (Crandell & Smaldino, 2004; Johnstone & Litovsky, 2006). This is particularly true for hearing-impaired children, especially those of a young age. We also know that children are able to orient toward sound sources at a very young age (Ashmead, Clifton & Perrin, 1987; Muir & Field, 1979; Muir, Clifton & Clarkson, 1989), so it follows that directional microphones could potentially improve their speech reception ability in the presence of competing sounds. However, because of concerns about reduced access to non-frontal speech and environmental sounds, audiologists are often reluctant to fit young children and infants with hearing aids equipped with directional settings for fear of detrimental effects on incidental learning.

Ching, O’Brien, Dillon, Chalupper, Hartley, Hartley, Raicevich and Hain (2009) investigated head orientation and the opportunity for young children to benefit from directional hearing aid use in everyday environments. Prior research had shown benefits of directionality in laboratory conditions (Bohnert & Brantzen, 2004; Condie, Scollie, & Checkley, 2002; Kuk, Kollofski, Brown, Melum & Rosenthal, 1999), but it was unknown how directionality would affect speech reception in more typical, naturalistic situations. The goal of the study was twofold: 1) to determine the potential benefit of directionality on reception of speech in naturalistic listening situations, and 2) to examine potentially detrimental effects of directionality on non-frontal sounds.

The authors recruited eleven children with normal hearing and sixteen children with moderate hearing loss between the ages of 11 months and 6.5 years. The children were fitted with behind-the-ear, wide dynamic range hearing aids with directional microphones. None of them had prior experience with directionality in their personal hearing aids.

Video recordings of the children were obtained, in four scenarios that represent everyday situations. Diary entries from parents and caregivers were collected to identify listening situations that could account for approximately 80% of child’s weekly routine. It was hoped that the diary entries could help predict how often the children were likely to be in situations where directionality could be beneficial.

The video recordings of the children in typical listening scenarios were used to evaluate the proportion of time that they were oriented toward primary speech sources. The four scenarios were:

* The child interacting directly with a caregiver in a play situation
* The child NOT interacting directly with adults in the same room
* The child indoors with other children and adults
* The child outdoors with other children and adults

During the recordings, the researchers logged the time during which speech was “present”. Speech was deemed “present” whenever a primary talker could be identified, whether or not they were addressing the child directly.

Video analysis revealed that in the one-to-one situation, the children oriented themselves toward the talker almost 60% of the time. In the remaining group scenarios, the children oriented toward the primary talker between 30-50% of the time, even if they were not being directly addressed by the talker. They were least likely to face the talker in the second scenario, in which adults were present but the child was not engaged in play with adults or other children. Interestingly, age and the presence of hearing loss did not affect the proportion of time that the children spent facing the talker.

Examination of the caregivers’ diaries revealed that the majority of the children’s time was spent on indoor activities, particularly in group situations. Children with normal hearing were slightly more likely to participate in group activities than hearing-impaired children were. Conversely, hearing-impaired children were somewhat more likely than normal-hearing children to participate in one-to-one activities.

Overall, it was determined that directionality had a positive effect on speech reception, because:
* children oriented themselves toward the primary talker more than 50% of the time
* directionality improved SNR for speech in front of the child, especially in group situations
* diary entries showed that the children frequently participated in group activities

It was also determined that directionality is not likely to have detrimental effects on the perception of incidental speech and environmental sounds. The children still oriented themselves to primary speech sources more than 40% of the time, even when talkers were not directly addressing them. Furthermore, the authors pointed out that the changes in SNR were small, which can be enough to have a significant effect on speech reception from the front in the presence of background noise, but is less likely to be enough to affect perception on dominant sound sources from the rear. It follows, then, that directional microphone settings in hearing aids could have benefits for young pediatric hearing aid users by improving the signal-to-noise ratio and therefore the reception of speech information, especially in group situations.

The authors advised that directional hearing aid programs, partly because of inherent decreases in low-frequency gain, might not always be advisable for children, especially in quiet conditions. They recommended the use of directional settings with equalized frequency responses to adjust for the reduction in low-frequency gain and suggested that switchable instruments would be best, to allow for omnidirectional hearing in quiet conditions and directionality in the presence of noise. Because young children and infants are not capable of adjusting hearing aid settings on their own, automatically adjustable instruments were suggested, especially those that can prioritize speech from a dominant talker even from non-frontal directions. Today we have a wide variety of automatically adjustable directional instruments available at a broad range of price points. This, coupled with ongoing improvements in speech enhancement and noise reduction in hearing aid circuitry indicate that clinicians will have even better tools to help hearing-impaired children function in noisy, everyday situations.

The authors underscored the importance of thoroughly counseling caregivers on the effects of directionality in various listening environments. For instance, caregivers should pay attention to the child’s head orientation and positioning and should initiate face-to-face communication at close proximity whenever possible, particularly in noisy situations. Clinical audiologists routinely counsel patients on proper positioning and the importance of face-to-face communication to reduce the effects of background noise on speech perception. Because young, hearing-impaired children rely on better signal-to-noise ratios to receive and process speech information in their everyday activities, and because they may not always orient themselves toward primary speech sources, it is particularly important for their caregivers to understand how they can help maximize the benefit of the child’s directional microphone hearing aids.

References:
Ashmead, D.H., Clifton, R.K. & Perrin, E.E. (1987). Precision of auditory localization in human infants. Developmental Psychology, 23, 641-647.

Bohnert, A., & Brantzen, P. (2004). Experiences when fitting children with a digital directional hearing aid. Hearing Review, 11, 50-55.

Ching, T.Y.C., O’Brien, A., Dillon, H., Chalupper, J., Hartley, L., Hartley, D., Raicevich, & Hain, J. (2009). Directional effects on infants and young children in real life: implications for amplification. Journal of Speech Language and Hearing Research, 52, 1241-1254.

Condie, R.K., Scollie, S.D., & Checkley, P. (2002). Children’s performance: Analog versus digital adaptive dual-microphone instruments. Hearing Review, 9, 40-43.

Crandell, C., & Smaldino, J. J. (2004). Classroom acoustics. In R.D. Kent (Ed.), The MIT Encyclopedia of communication disorders (pp 442-444). Cambridge, MA: The MIT Press.

Johnstone, P.M. & Litovsky, R.Y. (2006). Effect of masker type and age on speech intelligibility and spatial release from masking in children and adults. The Journal of the Acoustical Society of America, 120, 2177-2189.

Kuk, F., Kollofski, C., Brown, S., Melum, A., & Rosenthal, A. (1999). Use of a digital hearing aid with directional microphones in school-aged children. Journal of the American Academy of Audiology, 10, 535-548.

Muir, D., & Field, J. (1979). Newborn infants orient to sounds. Child Development, 50, 431-436.

Muir, D., Clifton, R.K., & Clarkson, M.G. (1989). The development of a human auditory localization response: A U-shaped function. Canadian Journal of Psychology, 3, 199-216.