Starkey Research & Clinical Blog

The Top 5 Audiology Research Articles from 2012

2012 was an impressive year for scientific publication in audiology research and hearing aids. Narrowing the selection to 15 or 20 articles was far easier than selecting 5 top contenders. After some thought and discussion, here is our selection of the top 5 articles published in 2012.


1. Implications of high-frequency cochlear dead regions for fitting hearing aids to adults with mild to moderately severe hearing loss

Cox, R.M., Johnson, J.A., & Alexander, G.C. (2012). Implications of high-frequency cochlear dead regions for fitting hearing aids to adults with mild to moderately severe hearing loss. Ear and Hearing, 33, 573-587.

This article is the second in a series that investigated relationships between cochlear dead regions and benefits received from hearing aids. A sample of patients, diagnosed with high-frequency cochlear dead regions, demonstrated superior outcomes when prescribed hearing aids with a broadband response; as compared to a response that limited audibility at 1,000 Hz. These findings clearly illustrate that patients with cochlear dead regions benefit from—and prefer—amplification at frequencies similar to those with diagnosed cochlear dead regions.

http://journals.lww.com/ear-hearing/Abstract/2012/09000/Implications_of_High_Frequency_Cochlear_Dead.2.aspx

2. The speech intelligibility index and the pure-tone average as predictors of lexical ability in children fit with hearing aids

Stiles, D.J., Bentler, R.A., & McGregor, K.K. (2012). The speech intelligibility index and the pure-tone average as predictors of lexical ability in children fit with hearing aids. Journal of Speech Language and Hearing Research, 55, 764-778.

The pure-tone threshold is the most commonly referenced diagnostic information when counseling families of children with hearing loss. This study compared the predictive value of pure-tone thresholds and the aided speech intelligibility index for a group of children with hearing loss. The aided speech intelligibility index proved to be a stronger predictor of word recognition, word repetition, and vocabulary. These observations suggest that a measure of aided speech intelligibility index is useful tool in hearing aid fitting and family counseling.

http://jslhr.asha.org/cgi/content/abstract/55/3/764

3. NAL-NL2 Empirical Adjustments

Keidser, G., Dillon, H., Carter, L., & O’Brien, A. (2012). NAL-NL2 Empirical Adjustments. Trends in Amplification, 16(4), 211-223.

The NAL-NL2 relies on several psychoacoustic models to derive target gains for a given hearing loss. Yet, it is well understood that these models are limiting and do not account for many individual factors. The inclusion of empirical adjustments to the NAL-NL2 highlights several factors that should be considered for prescribing gain to hearing aid users.

http://tia.sagepub.com/content/16/4/211.abstract

4. Initial-fit approach versus verified prescription: Comparing self-perceived hearing aid benefit

Abrams, H.B., Chisolm, T.H., McManus, M., & McArdle, R. (2012). Initial-fit approach versus verified prescription: Comparing self-perceived hearing aid benefit. Journal of the American Academy of Audiology, 23(10), 768-778.

While the outcomes of this study were not surprising, similar data had not been published in the refereed literature. The authors show that patients fit to a prescriptive target (i.e. NAL-NL1) report significantly better outcomes than patients fit to the lower gain targets that are offered in fitting softwares as ‘first-fit’ prescriptions. This study is a testimonial to the importance of counseling patients regarding audibility and the necessity of real-ear measurement to ensure audibility.

http://aaa.publisher.ingentaconnect.com/content/aaa/jaaa/2012/00000023/00000010/art00003

5. Conducting qualitative research in audiology: A tutorial

Knudsen, L.V., Laplante-Levesque, A., Jones, L., Preminger, J.E., Nielsen, C., Lunner, T., Hickson, L., Naylor, G., & Kramer, S.E. (2012). Conducting qualitative research in audiology: A tutorial. International Journal of Audiology, 51, 83-92.

A substantive majority of the audiologic research literature reports on quantitative data, discussing group outcomes and average trends. The challenges faced in capturing individual differences and clearly documenting field experiences require a different approach to data collection and analysis. Qualitative analysis leverages data from transcribed interviews or subjective reports to probe these anecdotal reports. This tutorial paper described methods for qualitative analysis and cites existing studies that have used these analyses.

http://informahealthcare.com.ezproxylocal.library.nova.edu/doi/abs/10.3109/14992027.2011.606283

Do hearing aid wearers benefit from visual cues?

Wu, Y-H. & Bentler, R.A. (2010) Impact of visual cues on directional benefit and preference: Part I – laboratory tests. Ear and Hearing 31(1), 22-34.

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 benefits of directional microphone use have been consistently supported by experimental data in the laboratory (Valente et al. 1995; Ricketts & Hornsby 2006; Gravel et al. 1999; Kuk et al. 1999). Similarly, hearing aid users have indicated a preference for directional microphones over omnidirectional processing in noise in controlled environments (Preves et al. 1999; Walden et al. 2005; Amlani et al. 2006). Despite the robust directional benefit reported in laboratory studies, field studies have yielded less impressive results; with some studies reporting perceived benefit (Preves et al. 1999; Ricketts et al. 2003) while others have not (Walden et al. 2000; Cord et al. 2002, 2004; Palmer et al. 2006).

One factor that could account for reduced directional benefit reported in field studies is the availability of visual cues. It is well established that visual cues, including lip-reading (Sumby & Pollack 1954) as well as eyebrow (Bernstein et al. 1989) and head movements (Munhall et al. 2004), can improve speech recognition ability in the presence of noise. In field studies, the availability of visual cues could result in a decreased directional benefit due to ceiling effects. In other words, the benefit of audio-visual (AV) speech cues might result in omnidirectional performance so close to a listener’s maximum ability that directionality may offer only limited additional improvement.  This could reduce both measured and perceived directional benefits.  It follows that ceiling effects from the availability of AV speech cues could also reduce the ability of auditory-only (AO) laboratory findings to accurately predict real-world performance.

Few studies have investigated the effect of visual cues on hearing aid performance or directional benefit. Wu and Bentler’s goal in the current study was to determine if visual cues could partially account for the discrepancy between laboratory and field studies of directional benefit. They outlined three experimental hypotheses:

1. Listeners would obtain less directional benefit and would prefer directional over omnidirectional microphone modes less frequently in auditory-visual (AV) conditions than in auditory-only (AO) conditions.

2. The AV directional benefit would not be predicted by the AO directional benefit.

3. Listeners with greater lip-reading skills would obtain less AV directional benefit than would listeners with lesser lip-reading skills.

Twenty-four adults with hearing loss participated in the study. Participants were between the ages of 20-79 years, had bilaterally symmetrical, downward-sloping, sensorineural hearing losses, normal or corrected normal vision and were native English speakers. Participants were fitted with bilateral, digital, in-the-ear hearing instruments with manually-accessible omnidirectional and directional microphone modes.

Directional benefit was assessed with two speech recognition measures:  the AV version of the Connected Speech Test (CST; Cox et al., 1987) and the Hearing in Noise Test (HINT; Nilsson et al., 1994). For the AV CST the talker was displayed on a 17” monitor. Participants listened to sets of CST sentences again in a second session to evaluate subjective preference for directional versus omnidirectional microphone modes. Speech stimuli were presented in six signal-to-noise (SNR) conditions ranging from -10dB to +10dB in 4db steps. Lip-reading ability was assessed with the Utley test (Utley, 1946), an inventory of 31 sentences recited without sound or facial exaggeration.

Analysis of the CST scores yielded significant main effects for SNR, microphone mode and presentation mode (AV vs. AO) as well as significant interactions among the variables. The benefit for visual cues was greater than the benefit afforded by directionality. As the authors expected, for most SNRs the directional benefit was smaller for AV conditions than AO conditions with the exception of the poorest SNR condition, -10dB.  Scores for all conditions (AV-DIR, AV-OMNI, AO-DIR, AO-OMNI) plateau at ceiling levels for the most favorable SNRs; meaning that both AV benefit and directional benefit decreased as SNR improved to +10dB.  HINT scores, which did not take into account ceiling effects, yielded a significant mean directional benefit of 3.9dB.

Participants preferred the directional microphone mode in the AO condition, especially at SNRs between -6dB to +2dB. At more favorable SNRs, there was essentially no preference. In the AV condition, participants were less likely to prefer the directional mode, except at the poorest SNR, -10dB. Further analysis revealed that the odds of preferring directional mode in AO condition were 1.37 times higher than in the AV condition. In other words, adding visual cues reduced overall preference for the directional microphone mode.

At intermediate and favorable SNRs there was no significant correlation between AV directional benefit and the Utley lip-reading scores. For unfavorable SNRs, the negative correlation between these variables was significant, indicating that in the most difficult listening conditions, listeners with better lip-reading skills obtained less AV directional benefit than those participants who were less adept at lip-reading.

The outcomes of these experiments generally support the authors’ hypotheses. Visual cues significantly improved speech recognition scores in omnidirectional trials close to ceiling levels, reducing directional benefit and subjective preference for directional microphone modes.  Auditory-only (AO) performance, typical of laboratory testing, was not predictive of auditory-visual (AV) performance. This is in agreement with prior indications that AO directional benefit as measured in laboratory conditions doesn’t match real-world directional benefit and suggests that the availability of visual cues can at least partially explain the discrepancy.  The authors suggested that directional benefit should theoretically allow a listener to rely less on visual cues. However, face-to-face conversation is natural and hearing-impaired listeners should leverage avoid visual cues when they are available.

The results of Wu and Bentler’s study suggest that directional microphones may provide only limited additional benefit when visual cues are available, for all but the most difficult listening environments. In the poorest SNRs, directional microphones may be leverages for greater benefit.  Still, the authors point out that mean speech recognition scores were best when both directionality and visual cues were available. It follows that directional microphones should be recommended for use in the presence of competing noise, especially in high noise conditions. Even if speech recognition ability is not significantly improved with the use of directional microphones in many typical SNRs, there may be other subjective benefits to directionality, such as reduced listening effort, distraction or annoyance that listeners respond favorably to.

It is important for clinicians to prepare new users of directional microphones to have realistic expectations. Clients should be advised that directionality can reduce competing noise but not eliminate it. Hearing aid users should be encouraged to consider their positioning relative to competing noise sources and always face the speech source that they wish to attend to.  Although visual cues appear to offer greater benefits to speech recognition than directional microphones alone; the availability of visual speech cues may be compromised by poor lighting, glare, crowded conditions or visual disabilities, making directional microphones all the more important for many everyday situations. Thus all efforts should be made to maximize directionality and the availability of visual cues in day-to-day situations, as both offer potential real-world benefits.

References

Amlani, A.M., Rakerd, B. & Punch, J.L. (2006). Speech-clarity judgments of hearing aid processed speech in noise: differing polar patterns and acoustic environments. International Journal of Audiology 12, 202-214.

Bernstein, L.E., Eberhardt, S.P. & Demorest, M.E. (1989). Single-channel vibrotactile supplements to visual perception of intonation and stress. Journal of the Acoustical Society of America 85, 397-405.

Cord, M.T., Surr, R.K., Walden, B.E., et al. (2002). Performance of directional microphone hearing aids in everyday life. Journal of the American Academy of Audiology 13, 295-307.

Cord, M.T., Surr, R.K., Walden, B.E., et al. (2004). Relationship between laboratory measures of directional advantage and everyday success with directional microphone hearing aids. Journal of the American Academy of Audiology 15, 353-364.

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

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

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

Lee L., Lau, C. & Sullivan, D. (1998). The advantage of a low compression threshold in directional microphones. Hearing Review 5, 30-32.

Leeuw, A.R. & Dreschler, W.A. (1991). Advantages of directional hearing aid microphones related to room acoustics. Audiology 30, 330-344.

Munhall, K.G., Jones, J.A., Callan, D.E., et al. (2004). Visual prosody and speech intelligibility: head movement improves auditory speech perception. Psychological Science 15, 133-137.

Nilsson, M., Soli, S. & 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, 1085-1099.

Palmer, C., Bentler, R., & Mueller, H.G. (2006). Evaluation of a second order directional microphone hearing aid: Part II – Self-report outcomes. Journal of the American Academy of Audiology 17, 190-201.

Preves, D.A., Sammeth, C.A. & Wynne, M.K. (1999). Field trial evaluations of a switched directional/omnidirectional in-the-ear hearing instrument.  Journal of the American Academy of Audiology 10, 273-284.

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

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

Ricketts, T. & Hornsby, B.W. (2006). Directional hearing aid benefit in listeners with severe hearing loss. International Journal of Audiology 45, 190-197.

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

Sumby, W.H. & Pollack, I. (1954). Visual contribution to speech intelligibility in noise. Journal of the Acoustical Society of America 26, 212-215.

Valente, M., Fabry, D.A. & 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., et al. (2000). Comparison of benefits provided by different hearing aid technologies. Journal of the American Academy of Audiology 11, 540-560.

Walden, B.E., Surr, R.K . Grant, K.W., et al. (2005). Effect of signal-to-noise ratio on directional microphone benefit and preference. Journal of the American Academy of Audiology 16, 662-676.

Wu, Y-H. & Bentler, R.A. (2010) Impact of visual cues on directional benefit and preference: Part I – laboratory tests. Ear and Hearing 31(1), 22-34.

Are you prescribing an appropriate MPO?

Effect of MPO and Noise Reduction on Speech Recognition in Noise

Kuk, F., Peeters, H., Korhonen, P. & Lau, C. (2010). Effect of MPO and noise reduction on speech recognition in noise. Journal of the American Academy of Audiology, submitted November 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 original authors.

A component of clinical best practice would suggest that clinicians determine a patient’s uncomfortable listening levels in order to prescribe the output limiting characteristics of a hearing aid (Hawkins et al., 1987). The optimal maximum power output (MPO) should be based on two goals: preventing loudness discomfort and avoiding distorted sound quality at high input levels. The upper limit of a prescribed MPO must allow comfortable listening; less consideration is given to the consequences that under prescribing MPO might have on hearing aid and patient performance.

There are two primary concerns related to the acceptable lower MPO limit: saturation and insufficient loudness. Saturation occurs when the input level of a stimulus plus gains applied by the hearing aid exceed the MPO, causing distortion and temporal smearing (Dillon & Storey, 1998). This results in a degradation of speech cues and a perceived lack of clarity, particularly in the presence of competing noise. Similarly, insufficient loudness reduces the availability of speech cues. There are numerous reports of subjective degradation of sound when MPO is set lower than prescribed levels, particularly in linear hearing instruments (Kuk et al., 2008; Storey et al., 1998; Preminger, et al., 2001). There is not yet consensus on whether low MPO levels also cause objective degradation in performance.

The purpose of the study described here was to determine if sub-optimal MPO could affect speech intelligibility in the presence of noise, even in a multi-channel, nonlinear hearing aid. Furthermore, the authors examined if gain reductions from a noise reduction algorithm could mitigate the detrimental effects of the lower MPO. The authors reasoned that a reduction in output at higher input levels, via compression and noise reduction, could reduce saturation and temporal distortion.

Eleven adults with flat, severe hearing losses participated in the reviewed study. Subjects were fitted bilaterally with 15-channel, wide dynamic range compression, behind-the-ear hearing aids. Microphones were set to omnidirectional and other than noise reduction, no special features were activated during the study. Subjects responded to stimuli from the Hearing in Noise Test (HINT, Nilsson et al., 1994) presented at a 0-degree azimuth angle in the presence of continuous speech-shaped noise. The HINT stimuli yielded reception thresholds for speech (RTS) scores for each test condition.

Test conditions included two MPO prescriptions: the default MPO level (Pascoe, 1989) and 10dB below that level. The lower setting was chosen based on previous work that reported an approximately 18dB acceptable MPO range for listeners with severe hearing loss  (Storey et al., 1998). MPOs set at 10dB below default would therefore be likely to approach the low end of the acceptable range, resulting in perceptual consequences. Speech-shaped noise was presented at two levels: 68dB and 75dB. Testing was done with and without digital noise reduction (DNR).

Analysis of the HINT RTS scores yielded significant main effects of MPO and DNR, as well as significant interactions between MPO and DNR, and DNR and noise level. There was no significant difference between the two noise level conditions. Subjects performed better with the default MPO setting versus the reduced MPO setting. The interaction between the MPO and DNR showed that subjects’ performance in the low-MPO condition was less degraded when DNR was activated. These findings support the authors’ hypotheses that reduced MPO can adversely affect speech discrimination and that noise reduction processing can at least partially mitigate these adverse effects.

Prescriptive formulae have proven to be reasonably good predictors of acceptable MPO levels (Storey et al., 1988; Preminger et al., 2001). In contrast, there is some question as to the value of clinical UCL testing prior to fitting, especially when validation with loudness measures is performed after the fitting (Mackersie, 2006). Improper instruction for the UCL task may yield inappropriately low UCL estimates, resulting in compromised performance and sound quality. The authors of the current paper recommend following prescriptive targets for MPO and conducting verification measures after the fitting, such as real-ear saturation response (RESR) and subjective loudness judgments.

Another scenario, and an ultimately avoidable one, involves individuals who have been fitted with inappropriate instruments for their loss, usually because of cosmetic concerns. It is unfortunately not so unusual for some individuals with severe hearing losses to be fitted with RIC or CIC instruments because of their desirable cosmetic characteristics. Smaller receivers will likely have MPOs that are too low for hearing aid users with severe hearing loss. Many hearing-aid users may not realize they are giving anything up when they select a CIC or RIC and may view these styles as equally appropriate options for their loss. The hearing aid selection process must therefore be guided by the clinician; clients should be educated about the benefits and limitations of various hearing aid options and counseled about the adverse effects of under-fitting their loss with a more cosmetically appealing option.

The results of the current study are important because they illuminate an issue related to hearing aid output that might not always be taken into clinical consideration. MPO settings are usually thought of as a way to prevent loudness discomfort, so the concern is to avoid setting the MPO too high. Kuk and his colleagues have shown that an MPO that is too low could also have adverse effects and have provided valuable information to help clinicians select appropriate MPO settings. Additionally, their findings show objective benefits and support the use of noise reduction strategies, particularly for individuals with reduced dynamic range due to severe hearing loss or tolerance issues. Of course their findings may not be generalizable to all multi-channel compression instruments, with the wide variety of compression characteristics that are available, but they present important considerations that should be examined in further detail with other instruments.

References

ANSI (1997). ANSI S3.5-1997. American National Standards methods for the calculation of the speech intelligibility index. American National Standards Institute, New York.

Dillon, H. & Storey, L. (1998). The National Acoustic Laboratories’ procedure for selecting the saturation sound pressure level of hearing aids: theoretical derivation. Ear and Hearing 19(4), 255-266.

Hawkins, D., Walden, B., Montgomery, A. & Prosek, R. (1987). Description and validation of an LDL procedure designed to select SSPL90. Ear and Hearing 8, 162-169.

Kuk , F., Korhonen, P., Baekgaard, L. & Jessen, A. (2008). MPO: A forgotten parameter in hearing aid fitting. Hearing Review 15(6), 34-40.

Kuk et al., (2010). Effect of MPO and noise reduction on speech recognition in noise. Journal of the American Academy of Audiology, submitted November 2010, fast track article.

Kuk, F. & Paludan-Muller, C. (2006). Noise management algorithm may improve speech intelligibility in noise. Hearing Journal 59(4), 62-65.

Mackersie, C. (2006). Hearing aid maximum output and loudness discomfort: are unaided loudness measures needed? Journal of the American Academy of Audiology 18 (6), 504-514.

Nilsson, M., Soli, S. & 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(2), 1085-1099.

Pascoe, D. (1989). Clinical measurements of the auditory dynamic range and their relation to formulae for hearing aid gain. In J. Jensen (Ed.), Hearing Aid Fitting: Theoretical and Practical Views. Proceedings of the 13th Danavox Symposium. Copenhagen: Danavox, pp. 129-152.

Preminger, J., Neuman, A. & Cunningham, D. (2001). The selection and validation of output sound pressure level in multichannel hearing aids. Ear and Hearing 22(6), 487-500.

Storey, L., Dillon, H., Yeend, I. & Wigney, D. (1998). The National Acoustic Laboratories, procedure for selecting the saturation sound pressure level of hearing aids: experimental validation. Ear and Hearing 19(4), 267-279.

Recommendations for fitting patients with cochlear dead regions

Cochlear Dead Regions in Typical Hearing Aid Candidates:

Prevalence and Implications for Use of High-Frequency Speech Cues

Cox, R.M., Alexander, G.C., Johnson, J. & Rivera, I. (2011).  Cochlear dead regions in typical hearing aid candidates: Prevalence and implications for use of high-frequency speech cues. Ear & Hearing 32 (3), 339-348.

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.

Audibility is a well-known predictor of speech recognition ability (Humes, 2007) and audibility of high-frequency information is of particular importance for consonant identification.  Therefore, audibility of high-frequency speech cues is appropriately regarded as an important element of successful hearing aid fittings (Killion & Tillman, 1982; Skinner & Miller, 1983). In contrast to this expectation, some studies have reported that high-frequency gain might have limited or even negative impact on speech recognition abilities of some individuals (Murray & Byrne, 1986; Ching et al., 1998; Hogan & Turner, 1998). These researchers observed that when high-frequency hearing loss exceeded 55-60dB, some listeners were unable to benefit from increased high-frequency audibility.  A potential explanation for this variability was provided by Brian Moore (2001), who suggested that an inability to benefit from amplification in a particular frequency region could be due to cochlear “dead regions” or regions where there is a loss of inner hair cell functioning.

Moore suggested that hearing aid fittings could potentially be improved if clinicians were able to identify patients with cochlear dead regions (DRs). Working under the assumption that diagnosis DRs may contraindicate high-frequency amplification. He and his colleagues developed the TEN test as a method of determining the presence of cochlear dead regions (Moore et al., 2000, 2004). The advent of the TEN test provided a standardized measurement protocol for DRs, but there is still wide variability in the reported prevalence of DRs. Estimates range from as 29% (Preminger et a., 2005) to as high as 84% (Hornsby & Dundas, 2009), with other studies reporting DR prevalence somewhere in the middle of that range. Several potential factors are likely to contribute to this variability, including degree of hearing loss, audiometric configuration and test technique.

In addition to the variability in reported prevalence of DRs, there is also variability in the reports of how DRs affect the ability to benefit from high-frequency speech cues (Vickers et al., 2001; Baer et al., 2002; Mackersie et al., 2004). It remains unclear as to whether high-frequency amplification recommendations should be modified to reflect the presence of DRs.  Most research is in agreement that as hearing thresholds increase, the likelihood of DRs also increases.  Hearing aid users with severe to profound hearing losses are likely to have at least one DR. Because a large proportion of hearing aid users have moderate to severe hearing losses, Dr. Cox and her colleagues wanted to determine the prevalence of DRs in this population. In addition, they examined the effect of DRs on the use of high-frequency speech cues by individuals with moderate to severe loss.

Their study addressed two primary questions:

1) What is the prevalence of dead regions (DRs) among listeners with hearing thresholds in the 60-90dB range?

2) For individuals with hearing loss in the 60-90dB range, do those with DRs differ from those without DRs in their ability to use high-frequency speech cues?

One hundred and seventy adults with bilateral, flat or sloping sensorineural hearing loss were tested. All subjects had thresholds of 60 to 90dB in the better ear for at least part of the range from 1-3kHz and thresholds no better than 25dB for frequencies below 1kHz. Subjects ranged in age from 38 to 96 years, and 59% of the subjects had experience with hearing aids.

First, subjects were evaluated for the presence of DRs with the TEN test. Then, speech recognition was measured using high-frequency emphasis (HFE) and high-frequency emphasis, low-pass filtered (HFE-LP) stimuli from the QSIN test (Killion et al. 2004). HFE items on this test are amplified up to 32dB above 2.5kHz, whereas the HFE-LP items have much less gain in this range. Comparison of subjects’ responses to these two types of stimuli allowed the investigators to assess changes in speech intelligibility with additional high frequency cues. Presentation levels for the QSIN were chosen by using a loudness scale and bracketing procedure to arrive at a level that the subject considered “loud but okay”. Finally, audibility differences for the two QSIN conditions were estimated using the Speech Intelligibility Index based on ANSI 3.5-1997 (ANSI, 1997).

The TEN test results revealed that 31% of the participants had DRs at one or more test frequencies. Of the 307 ears tested, 23% were found to have a DR for one or more frequencies. Among those who tested positive for DRs, about 1/3 had DRs in both ears and 2/3 had DRs in one ear or the other in equal proportion. Mean audiometric thresholds were essentially identical for the two groups below 1kHz, but above 1kHz thresholds were significantly poorer for the group with DRs than for the group without DRs.  DRs were most prevalent at frequencies above 1.5kHz. There were no age or gender differences.

On the QSIN test, the mean HFE-LP scores were significantly poorer than the mean HFE scores for both groups.  There was also a significant difference in performance based on whether or not the participants had DRs. Perhaps more interestingly, there was a significant interaction between the DR group and test stimuli conditions, in that the additional high-frequency information in the HFE stimuli resulted in slightly greater performance gains for the group without DRs than it did for the group with DRs.  Furthermore, subjects with one or more isolated DRs were more able to benefit from the high frequency cues in the HFE lists than were those subjects with multiple, contiguous DRs. Although there were a few isolated individuals who demonstrated lower scores for the HFE stimuli, the differences were not significant and could have been explained by measurement error. Therefore, the authors conclude that the additional high frequency information in the HFE stimuli was not likely to have had a detrimental effect on performance for these individuals.

As had also been reported in previous studies, subject groups with DRs had poorer mean audiometric thresholds than the groups without DRs, so it was possible that audibility played a role in QSIN performance. Analysis of the audibility of QSIN stimuli for the two groups revealed that high frequency cues in the HFE lists were indeed more audible for the group without DRs. In accounting for this audibility effect, the presence of DRs still had a small but significant effect on performance.

The results of this study suggest that listeners with cochlear DRs still benefit from high frequency speech cues, albeit slightly less than those without dead regions.  The performance improvements were small and the authors caution that it is premature to draw firm conclusions about the clinical implications of this study.  Despite the need for further examination, the results of the current study certainly do not support any reduction in prescribed gain for hearing aid candidates with moderate to severe hearing losses.  The authors acknowledge, however, that because the findings of this and other studies are based on group data, it is possible that specific individuals may be negatively affected by amplification within dead regions. Based on the research to date, this seems more likely to occur in individuals with profound hearing loss who may have multiple, contiguous DRs.

More study is needed to determine the most effective clinical approach to managing cochlear dead regions in hearing aid candidates. Future research should be done with hearing aid users, including for example, the effects of noise on everyday hearing aid performance for individuals with DRs. A study by Mackersie et. al. (2004) showed that subjects with DRs suffered more negatives effects of noise than did the subjects without DRs. If there is a convergence of evidence to this effect, then recommendations about the use of high frequency gain, directionality and noise reduction could be determined as they relate to DRs. For now, Dr. Cox and her colleagues recommend that until there are clear criteria to identify individuals for whom high frequency gain could have deleterious effects, clinicians should continue using best-practice protocols and provide high frequency gain according to current prescriptive methods.

References

ANSI ( 1997). American National Standard Methods for Calculation of the Speech Intelligibility Index (Vol. ANSI S3.5-1997). New York: American National Standards Institute.

Ching,T., Dillon, H. & Byrne, D. (1998). Speech recognition of hearing-impaired listeners: Predictions from audibility and the limited role of high-frequency amplification. Journal of the Acoustical Society of America 103, 1128-1140.

Cox, R.M., Alexander, G.C., Johnson, J. & Rivera, I. (2011).  Cochlear dead regions in typical hearing aid candidates: Prevalence and implications for use of high-frequency speech cues. Ear & Hearing 32 (3), 339-348.

Hogan, C.A. & Turner, C.W. (1998). High-frequency audibility: Benefits for hearing-impaired listeners. Journal of the Acoustical Society of America 104, 432-441.

Humes, L.E. (2007). The contributions of audibility and cognitive factors to the benefit provided by amplified speech to older adults. Journal of the American Academy of Audiology 18, 590-603.

Killion, M. C. & Tillman, T.W. (1982). Evaluation of high-fidelity hearing aids. Journal of Speech and Hearing Research 25, 15-25.

Moore, B.C.J. (2001). Dead regions in the cochlear: Diagnosis, perceptual consequences and implications for the fitting of hearing aids. Trends in Amplification 5, 1-34.

Moore, B.C.J., Huss, M., Vickers, D.A.,  et al. (2000). A test for the diagnosis of dead regions in the cochlea. British Journal of Audiology 34, 2-5-224.

Moore, B.C.J., Glasberg, B.R., Stone, M.A. (2004). New version of the TEN test with calibrations in dB HL. Ear and Hearing 25, 478-487.

Murray, N. & Byrne, D. (1986). Performance of hearing-impaired and normal hearing listeners with various high-frequency cut-offs in hearing aids. Australian Journal of Audiology 8, 21-28.

Skinner, M.W. & Miller, J.D. (1983). Amplification bandwidth and intelligibility of speech in quiet and noise for listeners with sensorineural hearing loss.  Audiology 22, 253-279.

A preferred speech stimulus for testing hearing aids

Development and Analysis of an International Speech Test Signal (ISTS)

Holube, I., Fredelake, S., Vlaming, M. & Kollmeier, B. (2010). Development and analysis of an international speech test signal (ISTS). International Journal of Audiology, 49, 891-903.

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.

Current hearing aid functional verification measures are described in the standards IEC 60118 and ANSI 3.22 and use stationary signals, including sine wave frequency sweeps and unmodulated noise signals. Test stimuli are presented to the hearing instrument and frequency specific gain and output is measured in a coupler or ear simulator.  Current standardized measurement methods require the instrument to be set at maximum or a reference test setting and adaptive parameters such as noise reduction and feedback management are turned off.

These procedures provide helpful information for quality assurance and determining fitting ranges for specific hearing aid models. However, because they were designed for linear, time-invariant hearing instruments, they have limitations for today’s nonlinear, adaptive instruments and cannot provide meaningful information about real-life performance in the presence of dynamically changing acoustic environments.

Speech is the most important stimulus encountered by hearing aid users and nonlinear hearing aids with adaptive characteristics process speech differently than they do stationary signals like sine waves and unmodulated noise. Therefore, it seems preferable for standardized test procedures to use stimuli that are as close as possible to natural speech.  Indeed, there are some hearing aid test protocols that use samples of natural speech or live speech. But natural speech stimuli will have different spectra, fundamental frequencies, and temporal characteristics depending on the speaker, the source material and the language. For hearing aid verification measures to be comparable to each other it is necessary to have standardized stimuli that can be used internationally.

Alternative test stimuli have been proposed based on the long-term average speech spectrum (Byrne et al., 1994) or temporal envelope fluctuations (Fastl, 1987). The International Collegium for Rehabilitative Audiology (ICRA) developed a set of stimuli (Dreschler, 2001) that reflect the long-term average speech spectrum and have speech-like modulations that differ across frequency bands.  ICRA stimuli have advantages over modulated noise and sine wave stimuli in that they share some similar characteristics with speech, but they lack speech-like comodulation characteristics (e.g., fundamental frequency). Furthermore, ICRA stimuli are often classified by signal processing algorithms as “noise” rather than “speech”, so they are less than optimal for measuring how hearing aids process speech.

The European Hearing Instrument Manufacturers Association (EHIMA) is developing a new measurement procedure for nonlinear, adaptive hearing instruments and an important part of their initiative is development of a standardized test signal or International Speech Test Signal (ISTS).  The development and analysis of the ISTS was described in a paper by Holube, et al. (2010).

There were fifteen articulated requirements for the ISTS, based on available test signals and knowledge of natural speech, the most clinically salient of which are:

  • The ISTS should resemble normal speech but should be non-intelligible.
  • The ISTS should be based on six major languages, representing a wide range of phonological structures and fundamental frequency variations.
  • The ISTS should be based on female speech and should deviate from the international long-term average speech spectrum (ILTASS) for females by no more than 1dB.
  • The ISTS should have a bandwidth of 100 to 16,000Hz and an overall RMS level of 65dB.
  • The dynamic range should be speech-like and comparable to published values for speech (Cox et al., 1988; Byrne et al., 1994).
  • The ISTS should contain voiced and voiceless components. Voiced components should have a fundamental frequency characteristic of female speech.
  • The ISTS should have short-term spectral variations similar to speech (e.g., formant transitions).
  • The ISTS should have modulation characteristics similar to speech (Plomp, 1984).
  • The ISTS should contain short pauses similar to natural running speech.
  • The ISTS stimulus should have a 60 second duration, from which other durations can be derived.
  • The stimulus should allow for accurate and reproducible measurements regardless of signal duration.

Twenty-one female speakers of six different languages (American English, Arabic, Mandarin, French, German and Spanish) were recorded while reading a story, the text and translations of which came from the Handbook of the International Phonetic Association (IPA).  One recording from each language was selected based on a number of criteria including voice quality, naturalness and median fundamental frequency. The recordings were filtered to meet the ILTASS characteristics described by Byrne et al. (1994) and were then split into 500ms segments that roughly corresponded to individual syllables. These syllable-length segments were attached in pseudo-random order to generate sections of 10 or 15 milliseconds. Each of the resulting sections could be combined to generate different durations of the ISTS stimulus and no single language was used more than once in any 6-segment section.  Speech interval and pause durations were analyzed to ensure that ISTS characteristics would closely resemble natural speech patterns.

For analysis purposes, a 60-second ISTS stimulus was created by concatenation of 10- and 15-second sections.  This ISTS stimulus was measured and compared to natural speech and ICRA-5 stimuli based on several criteria:

  • Long-term average speech spectrum (LTASS)
  • Short term spectrum
  • Fundamental frequency
  • Proportion of voiceless segments
  • Band-specific modulation spectra
  • Comodulation characteristics
  • Pause and speech duration
  • Dynamic range (spectral power level distribution)

On all of the analysis criteria, the ISTS stimulus resembled natural speech stimuli as well or better than ICRA-5 stimuli. Notable improvements for the ISTS over the ICRA-5 stimulus were its comodulation characteristics and dynamic range of 20-30dB, as well as pauses and combinations of voiced and voiceless segments that more closely resembled the distributions in natural speech.  Overall, the ISTS was deemed an appropriate speech-like stimulus proposal for the new standard measurement protocol.

Following the detailed analysis, the ISTS stimulus was used to measure four different hearing instruments, which were programmed to fit a flat, sensorineural hearing loss of 60dBHL.  Each instrument was nonlinear with adaptive noise reduction, compression and feedback management characteristics. The first-fit algorithms from each manufacturer were used, with all microphones fixed to an omnidirectional mode.  Instead of yielding gain and output measurements across frequency for one input level, the results showed percentile dependent gain (99th, 65th and 30th) across frequency as referenced to the long-term average speech spectrum.  The percentile dependent gain values provided information about nonlinearity, in that the softer components of speech were represented by the 30th percentile, moderate and loud speech components were represented by the 65th and 99th percentiles, respectively.  Relations between these three percentiles represented the differences in gain for soft, moderate and loud sounds.

The measurement technique described by Holube and colleagues, using the ISTS stimulus, offers significant advantages over current measurement protocols with standard sine wave or noise stimuli. First and perhaps most importantly, it allows hearing instruments to be programmed to real-life settings with adaptive signal processing features active. It measures how hearing aids process a stimulus that very closely resembles natural speech, so clinical verification measures may provide more meaningful information about everyday performance. By showing changes in percentile gain values across frequency, it also allows compression effects to be directly visible and may be used to evaluate noise reduction algorithms as well. The authors also note that the acoustic resemblance of ISTS to speech with its lack of linguistic information may have additional applications for diagnostic testing, telecommunications or communication acoustics.

The ISTS is currently available in some probe microphone equipment and will likely be introduced in most commercially available equipment over the next few years. Its introduction brings a standardized speech stimulus, for the testing of hearing aids, to the clinic. An important component of clinical best practice is the measurement of a hearing aid’s response characteristics. This is most easily accomplished through insitu probe microphone measurement in combination with a speech test stimulus such as the ISTS.

References

American National Standards Institute (ANSI ). ANSI S3.22-2003. Specification of hearing aid characteristics. New York: Acoustical Society of America.

Byrne, D., Dillon, H., Tran, K., Arlinger, S. & Wibraham, K. (1994). An international comparison of long0term average speech spectra. Journal of the Acoustical Society of America, 96(4), 2108-2120.

Cox, R.M., Matesich, J.S. & Moore, J.N. (1988). Distribution of short-term rms levels in conversational speech. Journal of the Acoustical Society of America, 84(3), 1100-1104.

Dreschler, W.A., Verschuure, H., Ludvigsen, C. & Westerman, S. (2001). ICRA noises: Artificial noise signals with speech-like spectral and temporal properties for hearing aid assessment. Audiology, 40, 148-157.

Fastl, H. (1987). Ein Storgerausch fur die Sprachaudiometrie. Audiologische Akustik, 26, 2-13.

Holube, I., Fredelake, S., Vlaming, M. & Kollmeier, B. (2010). Development and analysis of an international speech test signal (ISTS). International Journal of Audiology, 49, 891-903.

International Electrotechnical Commission, 1994, IEC 60118-0. Hearing Aids: Measurement of electroacoustical characteristics, Bureau of the International Electrotechnical Commission, Geneva, Switzerland.

IPA, 1999. Handbook of the International Phonetic Association. Cambridge University Press.

Plomp, R. (1984). Perception of speech as a modulated signal. In M.P.R. van den Broeche, A. Cohen (eds), Proceedings of the 10th International Congress of Phonetic Sciences, Utrecht, Dordrecht: Foris Publications, 29-40.

 

 

 

Will placing a receiver in the canal increase occlusion?

The influence of receiver size on magnitude of acoustic and perceived measures of occlusion.

Vasil-Dilaj, K.A., & Cienkowski, K.M. (2010). The influence of receiver size on magnitude of acoustic and perceived measures of occlusion. American Journal of Audiology 20, 61-68.

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 occlusion effect, an increase in bone conducted sound when the ear canal is occluded, is a consideration for many hearing aid fittings.  The hearing aid shell or earmold restricts the release of low-frequencies from the ear canal (Revit, 1992), resulting in an increase in low-frequency sound pressure level at the eardrum, sometimes up to 25dB (Goldstein & Hayes, 1965; Mueller & Bright, 1996; Westermann, 1987).  Hearing aid users suffering from occlusion will complain of an “echo” or “hollow” quality to their voices and hearing their own chewing can be particularly annoying. Indeed, perceived occlusion is reported to be a common reason for dissatisfaction with hearing aids (Kochkin, 2000).

Occlusion from a hearing aid shell or earmold is usually managed by increasing vent diameter or decreasing the length of the vent in order to decrease the acoustic mass of the vent (Dillon, 2001; Kiessling, et al, 2005). One potential risk of increasing vent diameter is increased risk of feedback, but this problem has been alleviated by improvements in feedback cancellation. Better feedback management has also resulted in more widespread use of open fit, receiver-in-canal (RIC) instruments which have proven effective in reducing measured and perceived occlusion (Dillon, 2001; Kiessling et al., 2005; Kiessling et al., 2003; Vasil & Cienkowski, 2006).

Though open fit BTE hearing instruments are designed to be acoustically transparent, some open fittings still result in perceived occlusion.  Interestingly, perceived occlusion is not always strongly or even significantly correlated with measured acoustic occlusion (Kiessling et al., 2005; Kuk et al., 2005; Kampe & Wynne, 1996), so it is apparent that other factors do contribute to the perception of occlusion.  The size of the receiver and/or eartip, as well as the size of the ear canal, affect the amount of air flow in and out of the ear canal and it seems likely that these factors could affect the amount of acoustic and perceived occlusion.

Thirty adults, 17 men and 13 women, participated in the study. All had normal hearing, unremarkable otoscopic examinations and normal tympanograms. Two measures of ear canal volume were obtained: volume estimates from the tympanometry screener and estimates determined from earmold impressions that were sent to a local hearing aid manufacturer.  Participants were fitted binaurally with RIC hearing instruments.  Instead of domes used clinically with RIC instruments flexible receiver sleeves designed specifically for research purposes were used.  Use of the special receiver sleeves allowed the researchers to increase the overall circumference of the receiver systematically so that six receiver size conditions could be evaluated:  no receiver, receiver only (with a circumference of 0.149 in.), 0.170 in., 0.190 in., 0.210in. and 0.230 in.

Real-ear unoccluded and occluded measures were obtained with subjects vocalizing the vowel /i/. Subjects monitored the level of their vocalizations via a sound level meter. Real ear occlusion effect (REOE) was determined by subtracting the SPL levels for the unoccluded response from the occluded response (REOR-REUR = REOE).  Subjective measures were obtained by asking subjects to rate their perception of occlusion on a five point scale ranging from “no occlusion” to “complete occlusion”. To avoid bias in the occlusion ratings, participants were not allowed to view the hearing aids or receiver sleeves until after testing was completed.

Results indicated that measured acoustic occlusion was very low for all conditions, especially below 500Hz, where it was below 2dB for most of the receiver conditions. For frequencies above 500Hz, REOE increased as receiver size increased. The no receiver and receiver only conditions had the least amount of measured occlusion and the largest receiver sizes had the most. There was no significant interaction between receiver size and frequency.

Perceived occlusion also increased as receiver size increased and though it was mild for most participants in most of the conditions, for the largest receiver condition, some participants rated occlusion as severe. Perceived occlusion was not significantly correlated with measured acoustic occlusion for low frequencies, and the two measures were only weakly correlated for frequencies between 700-1500Hz.

There was no significant relationship between either measure of ear canal volume and perceived or acoustic measures of occlusion. However, adequate ear canal volume to accommodate all receiver sizes was an inclusion criterion for the study, so the authors suggest that smaller ear canal volume could still be a factor in perceived or acoustic occlusion and may warrant further study.

The results of the current investigation show that occlusion was minimal for most of the receiver sizes. These findings are in agreement with previous studies of vented hollow molds, completely open IROS shells (Vasil & Cienkowski, 2006), large 2.4mm vents and silicone ear tips (Kiessling et al, 2005). REOEs for the two largest receivers matched results for a hollow mold with 1mm vent (Kuk et al, 2009) and the REOEs for the two smallest receivers matched results for hollow molds with 2mm and 3mm vents (Kuk et al, 2009).  The authors also point out that there was minimal insertion loss for all conditions. Insertion loss from closed earmolds can amount to 20dBHL (Sweetow, 1991) and can contribute to a perception of occlusion or poor voice quality.  The relative lack of insertion loss is yet another potential advantage of open and RIC fittings.

Perception of occlusion did increase with the size of the receiver, but overall differences were small. This is in agreement with prior research suggesting that reduction of air flow out of the ear canal results in more low-frequency energy in the ear canal (Revit, 1992), which can cause an increase in occlusion (Dillon, 2001). The authors point out that although subjects were not able to see the receivers prior to insertion, they were probably aware of the size and weight differences and could have been influenced by the perception of a larger object in the ear as opposed to actual occlusion. This may also be the case for hearing aid users, perhaps particularly so for individuals with smaller or tortuous ear canals.

The occlusion effect can be challenging, especially when anatomical or other constraints result in the use of minimal venting for individuals with good low-frequency hearing. The results reported here suggest that acoustic occlusion with RIC instruments is slight and may not always be related to perceived occlusion. Therefore, a client’s perception of “hollow” voice quality, “echoey” sound quality or a plugged sensation may be the most reliable indication of occlusion and the most important determinant of eartip size or venting characteristics. The administration of an occlusion rating scale or other self-evaluation techniques may also prove helpful in evaluating occlusion and its impact on overall hearing aid satisfaction.

References

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

Goldstein, D.P.,  & Hayes, C.S. (1965). The occlusion effect in bone conduction hearing.  Journal of Speech and Hearing Research 8, 137-148.

Kampe, S.D., & Wynne, M.K. ( 1996). The influence of venting on the occlusion effect. The Hearing Journal 49(4), 59-66.

Kiessling, J., Brenner, B., Jespersen, C.T., Groth, J., & Jensen, O.D. (2005). Occlusion effect of earmolds with different venting systems. Journal of the American Academy of Audiology, 16, 237-249.

Kiessling. J., Margolf-Hackl, S., Geller, S., & Olsen, S.O. (2003). Researchers report on a field test of a non-occluding hearing instrument. The Hearing Journal , 56(9), 36-41.

Kochkin, S. (2000). MarkeTrak V: Why my hearing aids are in the drawer: The consumer’s perspective. The Hearing Journal 53 (2), 34-42.

Kuk, F.K. , Keenan, D., & Lau, C.C. (2005). Vent configurations on subjective and objective occlusion effect. Journal of the American Academy of Audiology 16, 747-762.

Mueller, H.G., & Bright, K.E. (1996). The occlusion effect during probe microphone measurements. Seminars in Hearing 17 (1), 21-32.

Revit, L. (1992). Two techniques for dealing with the occlusion effect. Hearing Instruments 43 (12), 16-18.

Sweetow, R. W. (1991). The truth behind “non-occluding” earmolds. Hearing Instruments 42 (1), 25.

Vasil, K.A., & Cienkowski, K.M. (2006). Subjective and objective measures of the occlusion effect for open-fit hearing aids. Journal of the Academy of Rehabilitative Audiology 39, 69-82.

Vasil-Dilaj, K.A., & Cienkowski, K.M. (2010). The influence of receiver size on magnitude of acoustic and perceived measures of occlusion. American Journal of Audiology 20, 61-68.

Westermann, V.H. (1987). The occlusion effect. Hearing Instruments, 38 (6), 43.

The DSL 5.0a is a successful fitting formula for adults

Fit to Targets, Preferred Listening Levels, and Self-Reported Outcomes for the DSL v5.0a Hearing Aid Prescription for Adults

Polonenko, M.J., Scollie, S.D., Moodie, S., Seewald, R.C., Laurnagaray, D., Shantz, J. & Richards, A. (2010) Fit to targets, preferred listening levels and self-reported outcomes for the DSL v5.0a hearing aid prescription for adults. International Journal of Audiology 49, 550-560.

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 importance of perceived benefit for successful hearing aid fittings is well established. According to two MarkeTrak studies by Sergei Kochkin (2005, 2007), perceived benefit was the number one factor contributing to hearing aid user satisfaction.  Similarly, the lack of benefit was the most commonly cited reason for hearing aid returns.  Perceived benefit from hearing aids may be determined by a number of factors, but the appropriateness of the individually fitted gain is one of the main contributors (Cox & Alexander, 1994).

The Desired Sensation Level (DSL) prescriptive method was originally developed for children and prescribes targets that are generally very close to children’s preferred listening levels. However, DSL v4.1 targets have been found to prescribe gain that is 9 to 11 dB greater than adult preferred listening levels (Scollie et al., 2005).  Therefore, DSL v5.0a was developed with lower perceived loudness levels, ones that more closely approximate the needs of adult hearing aid users.

The success of a hearing aid prescription can be measured in terms of clinical efficacy, or how closely the hearing aid settings achieve a desired clinical result or test outcome. One such measure is the Preferred Listening Level (PLL). The PLL is defined as “the sound pressure level at the eardrum that the person chooses or prefers for listening to hearing aid amplified speech”(Cox & Alexander, 1994) and represents a compromise between comfort, intelligibility, background noise and distortion (Cox, 1982).  One method of measuring the PPL is by instructing listeners to adjust the volume setting of their hearing instruments to the level that sounds best to them, as they listen to speech presented at a conversational level.

A related but different way to determine the success of a hearing aid fitting strategy is measure effectiveness, or how well hearing aid settings help the user function in real-world situations.  One commonly used measure of hearing aid effectiveness is the Client Oriented Scale of Improvement or COSI (Dillon et al., 1997).  On the COSI questionnaire, the hearing aid user lists up to 5 typical listening situations in which he struggles to hear or would like to hear better.  Following a period of acclimatization, they rate the degree of perceived change in these situations as well as their final ability to function in each situation.

Although the DSL v5.0a prescriptive method was specifically developed for adults with acquired hearing loss, there have been relatively few studies evaluating it. Therefore the current authors sought to determine the electroacoustic feasibility, clinical efficacy, and effectiveness with adult hearing aid users. They had three primary goals:

1.  To measure final fit versus targets in a clinical environment

2.  To evaluate the preferred listening levels (PLLs) of adults versus the DSL v5.0a targets

3.  To measure the effectiveness of the DSL v5.0a prescription as reported on the COSI

Thirty subjects with predominantly sensorineural hearing loss participated in the study. Nineteen were new hearing aid users and eleven were experienced hearing aid users. Twenty-four were fitted binaurally, six were monaural users. Subjects were fitted in private clinics and the audiologists were specifically instructed to program and adjust the instruments to meet the patients’ needs, rather than to meet prescriptive targets.

Hearing aid fittings were matched to DSL 5.0 prescribed targets and verified with simulated real ear measurements, to ensure consistency between test sites and to promote replicable measures. Hearing aids were set to their primary programs and were measured in 2cc couplers, after individual Real Ear to Coupler Differences (RECD) were measured.  Following electroacoustic measures, the aids were fitted to the patients’ ears and adjustments were made based on patients’ subjective satisfaction. These procedures were not carried out according to any protocol established by the authors; the audiologists conducted fine tuning adjustments as needed for each individual. After an approximately 30-day period, subjects returned to the clinics for fine tuning.  After a total acclimatization period of 90 days, preferred listening levels (PLLs) and COSI outcome evaluations were conducted.

Electroacoustic analyses revealed that the clinical fittings were significantly correlated with the DSL v5.0a targets.  Sixty-eight percent of initial fittings were within 2.9 to 4.2 dB of target and 95% were within 5.8 to 8.4 dB of target across frequencies. These results contrast with previous research using NAL-R and NAL-NL1 targets, in which initial fittings differed from targets by 10-15dB. (Sammeth, 1993; Aazh and Moore, 2007).

Preferred listening levels (PLLs) were compared to targets and initial fittings and differed by only about 2dB.  The DSL v5.0a targets were on average 2.6dB lower than PLLs and 1.95dB lower than initial fittings.  Furthermore, DSL v5.0a targets were significantly correlated with PLLs at all frequencies and the targets and PLLs did not differ significantly as a function of degree of hearing loss.  The authors noted a trend for higher PLLs than targets at 250Hz, indicating that some users preferred more low-frequency output than prescribed.

COSI ratings of real-world performance were obtained at the 90-day appointment. The top five situations in which subjects hoped to hear better were similar to those chosen by subjects in the COSI normative study (Dillon et al, 1999):

1.  conversation with a group in noise

2.  conversation with a group in quiet

3.  conversation with one or two partners in noise

4.  listening to the television or radio

5.  conversation with one or two partners in quiet

Subjects were asked to rate the degree of change in their hearing with amplification as well as the final hearing ability (or hearing aid performance) in these situations. Results indicated that they judged their hearing to be “better” or “much better” for 83% of the fittings, which compares well to the normative results obtained by Dillon et al. (1999) of 80%. For final hearing ability, 93% of the current respondents reported hearing 75% of the time (a COSI rating of 4 or better) as compared to 90% of the normative study participants.

The purpose of the current study was to determine if DSLv5.0a prescriptive targets, developed for adults, provided electroacoustically appropriate fittings and subjectively favorable real-world results.  Indeed, clinician-adjusted fittings were within 10 dB of prescriptive targets for 92% of the subjects.  Targets also closely approximated preferred listening levels, which is particularly important because prior studies showed DSL v4.1 targets were generally higher than adults’ preferred levels.  COSI measurements indicated positive ratings for benefit and communication performance which were similar or slightly better than those obtained for the normative population.

An incidental finding of the current study was that instruments with more than six channels of processing may meet prescriptive targets more accurately than those with only six channels.  This was not specifically studied in the current paper, but the authors provided a matrix of number of channels versus errors in matching to target, showing that instruments with more than six channels yielded fewer and smaller errors than those with only six channels of processing. This result is probably consistent with clinical observations, in which sophisticated hearing aid circuits with more channels of processing often provide better fittings than instruments with fewer channels.  The importance of this factor may depend on the client’s hearing loss.  Gently sloping audiometric configurations may generally require fewer channels to meet targets.

The current results show that in a group of adults preferred listening levels and positive real-world outcomes were achieved with programs matched to DSL v5.0a targets, at least in quiet situations. In noisy listening situations, participants may have accessed alternate memories with directionality and noise reduction, causing amplification characteristics to differ from DSL settings.  Even if this is the case, the current study shows that the DSL v5.0a prescriptive measure for adults yields a close approximation to patient preferred settings for a wide range of hearing losses.

References

Aazh, H. &Moore, B.C.J. (2007). The value of routine real ear measurement of the gain of digital hearing aids. Journal of the American Academy of Audiology 18, 653-664.

Cox, R.M. (1982). Functional correlates of electroacoustic performance data. In: G.A. Studebaker & F.H. Bess (eds.) The Vanderbilt Hearing Aid Report. Parkton, MD: York Press, pp. 78-84.

Cox, R.M. & Alexander, G.C. (1994). Prediction of hearing aid benefit: the role of preferred listening levels. Ear and Hearing 15(1), 22-29.

Dillon, H., James, A. & Ginis, J. (1997). Client Oriented Scale of Improvement (COSI) and its relationship to several other measures of benefit and satisfaction provided by hearing aids. Journal of the American Academy of Audiology 8, 27-43.

Dillon, H., Birtles, G. & Lovegrove, R. (1999). Measuring the outcomes of a National Rehabilitation Program: normative data for the Client Oriented Scale of Improvement (COSI) and the Hearing Aid User’s Questionnaire (HAUQ). Journal of the American Academy of Audiology 10, 67-79.

Kochkin, S. (2005). MarkeTrak VII: Customer satisfaction with hearing instruments in the digital age. Hearing Journal 58(9), 30-43.

Kochkin, S. (2008). MarkeTrak VII:  Obstacles to adult non-user adoption of hearing aids. Hearing Journal 60(4), 24-51.

Polonenko, M.J., Scollie, S.D., Moodie, S., Seewald, R.C., Laurnagaray, D., Shantz, J. & Richards, A. (2010) Fit to targets, preferred listening levels and self-reported outcomes for the DSL v5.0a hearing aid prescription for adults. International Journal of Audiology 49, 550-560.

Sammeth, C., Peek, B., Bratt, G., Bess, F. & Amberg, S. (1993). Ability to achieve gain/frequency response and SSPL-90 under three prescription formulas with in-the-ear hearing aids. Journal of the American Academy of Audiology 4, 33-41.

Scollie, S., Seewald, R., Cornelisse, L., Moodie, S., Bagatto, M., et al. (2005). The Desired Sensation Level Multistage Input/Output Algorithm. Trends in Amplification 4(9), 159-197.

Understanding the benefits of bilateral hearing aids

A Prospective Multi-Centre Study of the Benefits of Bilateral Hearing Aids

Boymans, M., Goverts, S.T., Kramer, S.E., Festen, J.M. & Dreschler, W.A. (2008). A prospective multi-centre study of the benefits of bilateral hearing aids. Ear and Hearing 29(6), 930-941.

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 benefits of binaural amplification are generally well established and include improved speech discrimination in noise (Hawkins and Yacullo, 1984; Kobler & Rosenhall, 2002), improved localization of sound sources (Dreschler & Boymans, 1994; Punch et al, 1991) perception of balanced hearing, improved speech clarity (Chung & Stephens, 1986; Erdman & Sedge, 1981) and reduced listening  effort (Noble, 2006). However, some studies have shown either little subjective difference between unilateral and bilateral amplification (Andersson et al, 1996) or even a subjective preference for unilateral hearing aids, especially in noise (Walden & Walden, 2005; Schreurs & Olsen, 1985).

The authors of the current study sought to confirm subjective evaluations of binaural hearing aids with objective, functional tests of localization and speech discrimination in noise. They also examined three diagnostic measures to determine their potential as predictors of binaural success.

Two hundred fourteen hearing-impaired subjects were recruited from eight audiology clinics in the Netherlands. Participant inclusion criteria were limited only to  participants who were native Dutch speakers and were physically able to complete the test procedures, with no contraindications for binaural hearing aid fitting. Therefore, individual characteristics varied widely with regard to prior hearing aid use, hearing aid style and circuitry, age and degree of hearing loss. Ten participants with normal hearing were also tested for reference purposes.

Prior to hearing aid fitting, in addition to basic diagnostic audiometry, participants completed three tests that were chosen as potential predictors of binaural benefit:

1. Interaural time differences.

2. Binaural masking level differences.

3. Speech reception thresholds in background noise.

Following the hearing aid fittings, functional binaural benefit was evaluated and questionnaires were administered to obtain subjective responses to unilateral and bilateral fittings. Three assessment tools were used:

1. Speech intelligibility in background noise with spatial separation of speech and noise.

2. Horizontal localization of everyday sounds.

3. Subjective questionnaires to examine differences between unaided, unilateral, and bilateral conditions for detection of sounds, discrimination of sounds, speech intelligibility in quiet and noise, localization, and comfort of loud sounds.

Not surprisingly, on all three diagnostic measures, normal hearing participants performed significantly better than hearing-impaired participants. There was a great deal of inter-participant variability within the hearing-impaired group.

On the functional test of speech intelligibility with spatially separated speech and noise, bilateral hearing aid users performed significantly better than unilateral hearing aid users. Improvements were noted for conditions in which competing sounds were presented ipsilateral and contralateral to the speech stimulus.  On the localization test, bilateral hearing instrument wearers again performed significantly better than unilateral hearing aid wearers.  Subjective questionnaires showed that unilateral hearing aid use was favored over unaided conditions for all categories except comfort of loud sounds. Similarly, bilateral hearing aid use was favored over unilateral for all categories except comfort of loud sounds.  This finding is in agreement with previous work by the lead author of the current study (Boymans, 2003).

Participants were asked to provide reasons why they preferred one or two hearing aids. The most common reason for preferring a unilateral fitting was that the user’s own voice was more pleasant with one hearing aid. For preferred bilateral fittings, the most common reasons were, intelligibility on both sides, better localization, better sound quality, and better balance.  Following completion of the study, 93% of the participants chose to purchase bilateral hearing aids, whereas 7% chose to purchase only one hearing aid.

One primary goal of the study was to determine if subjective benefit could be supported with objective test results. There was a significant positive correlation between bilateral benefit for speech perception and subjective satisfaction ratings, but other evaluated factors did not show this relationship. Therefore, the authors determined that functional test results could not distinguish between groups who preferred unilateral or bilateral fittings. Overall, however, the vast majority of participants preferred bilateral hearing aid fittings and the functional test results support a strong binaural benefit.

The second goal of the study was to evaluate potential predictive measures of binaural benefit. The results did not show strong correlations between bilateral hearing aid performance and interaural time difference, binaural masking level difference or speech reception threshold measures.  Therefore, these measures were not determined to have particular predictive value for determining binaural hearing aid success.  In fact, the strongest correlation between bilateral benefit and any other diagnostic measure was found for traditional audiometric measures of pure tone average and maximum speech recognition.

Binaural benefit was also examined with regard to other subject variables. The authors found greater binaural benefit for users with more severe hearing loss and for those with more symmetrical hearing loss. There were no significant differences between subjects who had previously been fitted with unilateral hearing aids and those who had been previously fitted bilaterally. Participants without prior hearing aid experience demonstrated slightly less binaural benefit and less satisfaction than those with previous experience. The authors point out that this finding is confounded by the fact that previous users tended to have significantly greater degrees of hearing loss than first-time users.

The bilateral benefit for localization was higher for in-the-ear hearing aid users than for behind-the-ear hearing aid users. The authors surmised that this could be related to pinna effects, but pinna effects generally aid vertical localization and front/back localization (Blauert, 1997), whereas the localization measures in the current study were strictly horizontal. Still, it is possible that preservation of pinna-related spectral cues in combination with binaural cues could have had an additive effect for the in-the-ear hearing aid users in the present study.

It is interesting to note that despite the highly variable subject population in this study, significant binaural benefit for speech intelligibility and localization was found across participants, and participants overwhelmingly preferred the use of binaural hearing aids over monaural. Variables such as microphone mode, noise reduction technology, and circuit quality were not specifically addressed or controlled. It is reasonable to surmise that performance in the one category in which subjects preferred unilateral hearing aids, comfort for loud sounds, could be improved by adjustments to noise reduction settings, MPO or gain settings, or use of adaptive directionality.  Therefore, the study as a whole offers strong support for binaural hearing aid recommendations and indicates that the only negative effect, that of loudness discomfort, could probably be easily corrected with current technology.

Participants in this study were all willing to consider binaural hearing aid use and therefore had relatively symmetrical hearing losses. The binaural benefits measured here can probably be reasonably extrapolated to individuals with asymmetrical hearing losses, but this issue might benefit from further study.  Also, it is likely that similar binaural benefits may also apply to potential hearing aid users who are unwilling or reluctant to consider binaural hearing aid use, but these clients will require more thorough counseling with regard to expectations and acclimatization.  The primary reason given for unilateral hearing aid preference was related to occlusion and the sound quality of one’s own voice. A reluctant user of new binaural hearing aids will need to understand that this is a common, but often short-lived, outcome of binaural hearing aid use.

Because of the poor predictive value of diagnostic tests for binaural hearing aid success, the authors advise that it is probably best for hearing aid users to determine binaural benefit individually, during their initial trial period. This is appropriate advice and may be in line with what most clinicians are already recommending to their patients. Because an individual’s work, home, and social activities are important determinants of their perceived hearing handicap, binaural hearing aids should always be tested thoroughly in these situations to evaluate benefit.  There is little financial risk involved, as most clinics offer at least a 30-day trial period with new instruments and many offer a 45- or 60-day trial. Should a client determine that the benefit of a second hearing aid does not outweigh the financial burden, they would be able to return the aid for a refund, losing only the cost of a custom earmold and/or a trial period fee.

The current study shows strong evidence for functional improvements as well as perceived advantages in binaural hearing aid users. However, the authors were unable to identify a diagnostic tool to effectively predict binaural success.  This raises an important question about the value of such a predictive measure.  The significant improvements enjoyed by binaural users and the overwhelming preference for two hearing aids over one suggest that binaural fittings should be the recommendation of choice for all clients with bilateral, aidable hearing loss.  Granted, there are some audiometric findings that preclude a binaural recommendation, such as profound hearing loss in one ear, normal hearing in one ear, or exceptionally poor word recognition ability in one ear. But these are obvious, well-known, and relatively uncommon clinical contraindications to binaural hearing aid use. It seems reasonable, as the authors eventually suggest, to forego predictive measures and allow clients to experience binaural benefits individually and determine the proper decision for themselves during their trial period.

References

Andersson, G., Palmkvist, A., Melin, L. (1996). Predictors of daily assessed hearing aid use and hearing capability using visual analogue scales. British Journal of Audiology 30, 27-35.

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

Boymans, M. (2003). Intelligent processing to optimize the benefits of hearing aids. Ph.D. thesis, University of Amsterdam.

Boymans, M., Goverts, S.T., Kramer, S.E., Festen, J.M. & Dreschler, W.A. (2008). A prospective multi-centre study of the benefits of bilateral hearing aids. Ear and Hearing 29(6), 930-941.

Chung, S.M. & Stephens, S.D. (1986).  Factors influencing binaural hearing aid use. British Journal of Audiology 20, 129-140.

Dreschler, W.A. & Boymans, M. (1994). Clinical evaluation on the advantage of binaural hearing aid fittings. Audiologische Akustik 5, 12-23.

Erdman, S.A.  & Sedge, R.K. (1981). Subjective comparisons of binaural versus monaural amplification. Ear and Hearing 2, 225-229.

Hawkins, D.B. & Yacullo, W.S. (1984). Signal-to-noise ratio advantage of binaural hearing aids and directional microphones under different levels of reverberation. Journal of Speech and Hearing Disorders 49, 278-186.

Kobler, S. & Rosenhall, U. (2002). Horizontal localization and speech intelligibility with bilateral and unilateral hearing aid amplification. International Journal of Audiology 41, 395-400.

Noble, W. (2006). Bilateral hearing aids: a review of self-reports of benefit in comparison with unilateral fitting. International Journal of Audiology 45, 63-71.

Punch, J.L., Jenison, R.L. & Alan, J. (1991). Evaluation of three strategies for fitting hearing aids binaurally. Ear and Hearing 12, 205-215.

Schreurs, K.K. & Olsen, W.O. (1985). Comparison of monaural and binaural hearing aid use on a trial period basis. Ear and Hearing 6, 198-202.

Walden, T.C. & Walden, B.E. (2005). Unilateral versus bilateral amplification for adults with impaired hearing. Journal of the American Academy of Audiology 16, 574-584.

Comparing localization ability with BTE and CIC hearing aids

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.

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

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.