Starkey Evidence Blog

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

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

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

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

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

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

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

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

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

References

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

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

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

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

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

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

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

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

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

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

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

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

Article of interest:

Variation in Preferred Gain with Experience for Hearing-Aid Users

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

References

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Article of interest:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

References

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

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

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

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

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

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

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

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

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

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

Reviewing the benefits of open-fit hearing aids

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.

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

Article of interest:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

References

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

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

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

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

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

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

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

This editorial reviews the published article:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

The effect of digital noise reduction on listening effort: an article review

This article marks the first in a monthly series for StarkeyEvidence.com.

Each month scholarly journals publish articles on a wide array of topics. Some of these valuable articles and their useful conclusions never reach professionals in the clinical arena. The aim of these entries is to discuss research findings and their implications for hearing professionals living a daily clinical routine. Some of these topics may have general clinical relevance, while other may target specific aspects of hearing aids and their application.

This first discussion revolves around an article by authors Sarampalis, Kalluri, Edwards, and Hafter entitled “Objective measures of listening effort: Effects of background noise and noise reduction”. In this 2009 study, the authors pursue the sometimes elusive benefits of digital noise reduction. A review of past literature suggests that digital noise reduction, as implemented in hearing aids, benefits patients through improved sound quality, ease of listening and a possible perceived improvement in speech understanding. Significant improvements in speech understanding are, however, not a routinely observed benefit of digital noise reduction and some studies have shown significant decreases in speech understanding with active digital noise reduction.

In a 1992 article, authors Hafter and Schlauch suggest that noise reduction may lighten a patient’s cognitive load, essentially freeing resources for other tasks. To better understand the proposed effect, imagine driving a car in an unfamiliar area. It’s common for drivers to turn their stereo down, or off, when driving in a demanding situation. This is beneficial, not because music affects driving ability, but because the additional auditory input is distracting, effectively increasing the driver’s cognitive load. By removing the distraction of the stereo, more cognitive resources are freed and the ability to focus, or pay attention to the complex task of driving is improved.

In order to better understand how digital noise reduction may affect attention and cognitive load, two experiments were completed. In the first experiment, research participants were asked to repeat the last word of sentences presented in a background of noise. After eight sentences the listener attempted to repeat as many of the target words as they could. The sentence material contained both high-context and no-context conditions, for example:

High context: A chimpanzee is an ape

No context: She might have discussed the ape

In the second experiment listeners were asked to judge if a random number between one and eight was even or odd, while at the same time listening to and repeating sentences presented in a background of noise. Both experiments incorporated a dual-task paradigm: the first asked participants to repeat select words presented in noise, while also remembering these words for later recall. The second required participants to repeat an entire sentence, presented in noise, while also completing a complex visual task.

Highlights from experiment one show:

• performance in all conditions decreased as the signal-to-noise ratio became more difficult;
• overall performance in the no-context conditions was lower than in the high-context conditions;
• a comparison between performance with and without digital noise reduction showed a significant improvement in recall ability with digital noise reduction

 Highlights from experiment two show:

• performance in all conditions decreased as the signal-to-noise ratio became more difficult;
• reaction times increased with decreased signal-to-noise ratio;
• at -6 dB SNR, reaction times were significantly improved with digital noise reduction

 The findings of this study show that the cognitive demands of non-auditory tasks, such as visual and memory tasks, inhibit the ability of a person to understand speech-in-noise. In other words, secondary tasks make speech understanding more difficult. Additionally, digital noise reduction algorithms can reduce cognitive effort under adverse listening conditions. The authors discuss the value of using cognitive measures in hearing aid research and speculate that directional microphones may provide a cognitive benefit as well.

The clinical implications of this study suggest that patients may find benefits of wearing hearing aids that go beyond improved speech audibility. Modern signal processing may provide benefits that are only now being understood. For instance, a patient may report that hearing aids have made listening easier, that their new hearing instruments seem to suppress noise more than the old ones, but routine evaluation of speech understanding may not show significant differences between the two hearing aids.

Hearing aid success and benefit has traditionally been defined with the results of speech testing, or questionnaires. If advanced technology can ease the task of listening, patients may be receiving benefits from their hearing aids that we are not currently prepared to evaluate in the clinic. Hopefully, work in this area will continue, increasing our understanding of the role that cognition plays in the success of the hearing aid wearer. 

References:
Bentler, R., Wu, Y., Kettle, J., & Hurtig, R. (2008). Digital Noise Reduction: Outcomes from laboratory and field studies. International Journal of Audiology, 47:8, 447-460.

Hafter, E. R., & Schlauch, R. S. (1992). Cognitive factors and selection of auditory listening bands. In A. Dancer, D. Henderson, R. J. Salvi, & R. P. Hammernik ( Eds.), Noise-induced hearing loss (pp. 303–310). Philadelphia: B.C. Decker.

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