Starkey Research & Clinical Blog

Differences Between Directional Benefit in the Lab and Real-World

Relationship Between Laboratory Measures of Directional Advantage and Everyday Success with Directional Microphone Hearing Aids

Cord, M., Surr, R., Walden, B. & Dyrlund, O. (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.

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.

People with hearing loss require a better signal-to-noise ratio (SNR) than individuals with normal hearing (Dubno et al, 1984; Gelfand et al, 1988; Bronkhorst and Plomp, 1990).  Among many technological improvements, a directional microphone is arguably the only effective hearing aid feature for improving SNR and subsequently, improving speech understanding in noise. A wide range of studies support the benefit of directionality for speech perception in competing noise (Agnew & Block, 1997; Nilsson et al, 1994; Ricketts and Henry, 2002; Valente, 1995) Directional benefit is defined as the difference in speech recognition ability between omnidirectional and directional microphone modes. In laboratory conditions, directional benefit averages around 7-8dB but varies considerably and has ranged from 2-3dB up to 14-16dB (Valente et al, 1995; Agnew & Block, 1997).

An individual’s perception of directional benefit varies considerably among hearing aid users. Cord et al (2002) interviewed individuals who wore hearing aids with switchable directional microphones and 23% reported that they did not use the directional feature. Many respondents said they had initially tried the directional mode but did not notice adequate improvement in their ability to understand speech and therefore stopped using the directional mode. This discrepancy between measured and perceived benefit has prompted exploration of the variables that affect performance with directional hearing aids. Under laboratory conditions, Ricketts and Mueller (2000) examined the effect of audiometric configuration, degree of high frequency hearing loss and aided omnidirectional performance on directional benefit, but found no significant interactions among any of these variables.

The current study by Cord and her colleagues examined the relationship between measured directional advantage in the laboratory and success with directional microphones in everyday life. The authors studied a number of demographic and audiological variables, including audiometric configuration, unaided SRT, hours of daily hearing aid use and length of experience with current hearing aids, in an effort to determine their value for predicting everyday success with directional microphones.

Twenty hearing-impaired individuals were selected to participate in one of two subject groups. The “successful” group consisted of individuals who reported regular use of omnidirectional and directional microphone modes. The “unsuccessful” group of individuals reported not using their directional mode and using their omnidirectional mode all the time. Analysis of audiological and demographic information showed that the only significant differences in audiometric threshold between the successful and unsuccessful group were at 6-8 kHz, otherwise the two groups had very similar audiometric configurations, on average. There were no significant differences between the two groups for age, unaided SRT, unaided word recognition scores, hours of daily use or length of experience with hearing aids.

Subjects were fitted with a variety of styles – some BTE and some custom – but all had manually accessible omnidirectional and directional settings. The Hearing in Noise Test (HINT; Nilsson et al, 1994) was administered to subjects with their hearing aids in directional and omnidirectional modes. Sentence stimuli were presented in front of the subject and correlated competing noise was presented through three speakers: directly behind the subject and on each side. Following the HINT participants completed the Listening Situations Survey (LSS), a questionnaire developed specifically for this study. The LSS was designed to assess how likely participants were to encounter disruptive background noise in everyday situations, to determine if unsuccessful and successful directional microphone users were equally likely to encounter noisy situations in everyday life.  The survey consisted of four questions:

1) On average, how often are you in listening situations in which bothersome background noise is present?

2) How often are you in social situations in which at least 3 other people are present?

3) How often are you in meetings (e.g. community, religious, work, classroom, etc.)?

4) How often are you talking with someone in a restaurant or dining hall setting?

The HINT results suggest average directional benefit of 3.2dB for successful users and 2.1dB for unsuccessful users. Although directional benefit was slightly greater for the successful users, the difference between the groups was not statistically significant.  There was a broad range of directional benefit for both groups: from -0.8 to 6.0dB for successful users and from -3.4 to 10.5dB for the unsuccessful users. Interestingly, three of the ten successful users obtained little or no directional benefit, whereas seven of the ten unsuccessful users obtained positive directional benefit.

Analysis of the LSS results showed that successful users of directional microphones were somewhat more likely than unsuccessful users to encounter listening situations with bothersome background noise and to encounter social situations with more than three other people present. However, statistical analysis showed no significant differences between the two groups for any items on the LSS survey, indicating that users who perceived directional benefit and used their directional microphones were not significantly more likely to encounter noisy situations in everyday life.

These observations led the authors to conclude that directional benefit as measured in the laboratory did not predict success with directional microphones in everyday life. Some participants with positive directional advantage scores were unsuccessful directional microphone users and conversely, some successful users showed little or no directional advantage. There are a number of potential explanations for their findings. First, despite the LSS results, it is possible that unsuccessful users did not encounter real-life listening situations in which directional microphones would be likely to help. Directional microphone benefit is dependent on specific characteristics of the listening environment (Cord et al, 2002; Surr et al, 2002; Walden et al, 2004), and is most likely to help when the speech source is in front of and relatively close to the listener, with spatial separation between the speech and noise sources. Individuals who rarely encounter this specific listening situation would have limited opportunity to evaluate directional microphones and may therefore perceive only limited benefit from them.

Unsuccessful directional microphone users may have also had unrealistically high expectations about directional benefits. Directionality can be a subtle but effective way of improving speech understanding in noise. Reduction of sound from the back and sides helps the listener focus attention on the speaker and ignore competing noise. Directional benefit is based on the concept of face-to-face communication, if users expect their hearing aids to reduce all background noise from all angles they are likely to be disappointed. Similarly, if they expect the aids to completely eliminate background noise, rather than slightly reduce it, they will be unimpressed. It is helpful for hearing aid users, especially those new to directional microphones, to be counseled about realistic expectations as well as proper positioning in noisy environments. If listeners know what to expect and are able to position themselves for maximum directional effect they are more likely to perceive benefit from their hearing aids in noisy conditions.

To date, it has been difficult to correlate directional benefit under laboratory conditions with perceived directional benefit. It is clear that directionality offers performance benefits in noise, but directional benefit measured in a sound booth does not seem to predict everyday success with directional microphones. There are many factors that are likely affect real-life performance with directional microphone hearing aids, including audiometric variables, the frequency response and gain equalization of the directional mode, the venting of the hearing aid and the contribution of visual cues to speech understanding (Ricketts, 2000a; 2000b). Further investigation is still needed to elucidate the impact of these variables on the everyday experiences of hearing aid users.

As is true for all hearing aid features, directional microphones must be prescribed appropriately and hearing aid users should be counseled about realistic expectations and appropriate circumstances in which they are beneficial. Although most modern hearing instruments have the ability to adjust automatically to changing environments, manually accessed directional modes offer hearing aid wearers increased flexibility and may increase use by allowing the individual to make decisions regarding their improved comfort and performance in noisy places. Routine reinforcement of techniques for proper directional microphone use are encouraged. Hearing aid users should be encouraged to experiment with their directional programs to determine where and when they are most helpful. For the patient, proper identification of and positioning in noisy environments is essential step toward meeting their specific listening needs and preferences.

References

Agnew, J. & Block, M. (1997). HINT thresholds for a dual-microphone BTE. Hearing Review 4, 26-30.

Bronkhorst, A. & Plomp, R. (1990). A clinical test for the assessment of binaural speech perception in noise. Audiology 29, 275-285.

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

Cord, M., Surr, R., Walden, B. & Dyrlund, O. (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.

Dubno, J.R., Dirks, D.D. & Morgan, D.E. (1984).  Effects of age and mild hearing loss on speech recognition in noise. Journal of the Acoustical Society of America 76, 87-96.

Gelfand, S.A., Ross, L. & Miller, S. (1988). Sentence reception in noise from one versus two sources: effects of aging and hearing loss. Journal of the Acoustical Society of America 83, 248-256.

Kochkin, S. (1993). MarkeTrak III identifies key factors in determining customer satisfaction. Hearing Journal 46, 39-44.

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

Ricketts, T. (2000a). Directivity quantification in hearing aids: fitting and measurement effects. Ear and Hearing 21, 44-58.

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

Ricketts, T. (2001). Directional hearing aids. Trends in Amplification 5, 139-175.

Ricketts, T.  & Henry, P. (2002). Evaluation of an adaptive, directional microphone hearing aid. International Journal of Audiology 41, 100-112.

Ricketts, T. & Henry, P. (2003). Low-frequency gain compensation in directional hearing aids. American Journal of Audiology 11, 1-13.

Ricketts, T. & Mueller, H.G. (2000). Predicting directional hearing aid benefit for individual listeners. Journal the American Academy of Audiology 11, 561-569.

Surr, R.K., Walden, B.E. Cord, M.T. & Olson, L. (2002). Influence of environmental factors on hearing aid microphone preference. Journal of the American Academy of Audiology 13, 308-322.

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. & Dyrlund, O. (2004). Predicting microphone preference in everyday living. Journal of the American Academy of Audiology 15, 365-396.

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.

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.

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.

Considerations for Directional Microphone Use in the Classroom

Directional Benefit in Simulated Classroom Environments

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

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

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

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

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

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

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

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

2) Teacher Back – speech presented behind the listener.

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

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

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

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

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

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

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

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

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

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

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

References

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.

Reviewing the benefits of open-fit hearing aids

Article of interest:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Nilsson, M., Soli, S. and Sullivan, J. (1994). Development of the hearing in noise test for the measurement of speech reception thresholds in quiet and in noise. Journal of the Acoustical Society of America 95, 1085-1099.

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

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

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

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

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

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

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