Posted by Jason Galster on Wed, Jun 30, 2010 @ 01:48 PM
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:
- NAL-NL1 target response
- NAL-NL1 with a 6dB high-frequency cut at 3000Hz (HFC)
- NAL-NL1 with a 6dB low-frequency cut at 500Hz (LFC)
Subjects were asked to compare the programs in everyday environments and record their preferred overall program. Follow-up testing was conducted at 1 month, 4 months and 13 months post-fitting and subjects were specifically instructed to arrive at each appointment with the device on their overall preferred program and volume control setting. At each appointment, 2-cc coupler and real-ear measurements were obtained with hearing instruments at the preferred settings. Questionnaires were administered to record hearing aid usage time, ranking and performance of the three programs and to what extent the volume control was used. Loudness perception tests were performed using a categorical loudness scale test (Cox & Alexander, 1997) to determine the median SPL levels that were categorized as "comfortable".
The authors found that new and experienced users preferred the high-frequency cut (HFC) program most often. Initially, about 60% of the new users preferred the HFC program, but by 13 months post-fitting the preferences of new and experienced users were very similar with approximately half of the subjects still preferring the HFC program. Fewer than 10% of the users preferred the LFC program across the duration of the study.
On average, overall preferred gain was 3dB lower for new users and increases were noted at subsequent appointments. By the time of the final appointment, new users reported higher gain settings than they did before, but did not reach the preferred levels of experienced users. This suggests that the gain acclimatization process for some users may continue beyond the 13-month point. Degree of hearing loss had a significant effect, as subjects with moderate hearing loss preferred 6dB lower overall gain than those with mild hearing loss.
The findings of Keidser and colleagues offer important implications for clinical practice. First, it appears that new hearing aid users experience acclimatization with regard to comfortable loudness and preferred gain settings. This supports the use of adaptation levels in hearing aid software, though some adaptation managers may provide larger decrements in overall gain (5-10dB) than many hearing aid users require. The fact that new users with mild hearing loss did not prefer as much initial gain reduction as those with moderate losses indicates that audiometric thresholds should be considered. The authors noted that more information is needed about acclimatization effects in new hearing aid users with more than moderate hearing loss. However, it is probably appropriate for clinicians to assume that for patients with moderate to severe hearing loss, lower initial gain settings may be needed and an extended period of adjustment may be expected.
Recent emphasis on evidence-based clinical practice underscores the importance of verification measures to ensure adequate gain and frequency response from new hearing aids. However, study of auditory acclimatization demonstrates that it is equally important to evaluate the patient's perception of the amplified sound to ensure satisfaction. Ultimately, a patient with excellent aided test results may still reject new hearing aids if they are not comfortable.
Hearing aid acclimatization can be measured several ways, many of which are not viable for busy clinical practices. But there are two simple ways in which it should be addressed during the hearing aid fitting and follow-up appointments. At the fitting appointment, patients should be counseled about appropriate expectations for the adjustment process. For instance, patients who know ahead of time that it is normal to notice, and perhaps be slightly annoyed by, newly amplified sounds are less likely to be disheartened when this occurs. They should be advised to wear their hearing aids as consistently as possible and to report any discomfort or pain so it can be addressed with programming adjustments.
Initially, high frequency gain in particular may need to be reduced relative to target settings. However, care should be taken to determine each individual's comfort with high frequency sounds. In the current study, individuals were free to reduce high frequency gain at any time by selecting the HFC program. It seems appropriate to question whether this affected their ability to adjust to high-frequency gain and if they would have eventually been able to tolerate, even prefer, more high-frequency amplification had they not been able to switch at will into the HFC program. The importance of high-frequency information for speech intelligibility, especially in noise, is well established (Turner & Henry, 2002; Hornsby & Ricketts, 2003). To avoid detrimental effects on speech perception, high frequency gain should approach targets as closely as possible, while still maintaining patient comfort.
At follow-up appointments, patients should be questioned in detail about their comfort and overall progress with the new aids. Formal questionnaires like the APHAB (Cox and Alexander, 1995) can be used to determine specific sound preferences so that appropriate adjustments can be made. The more precise information a clinician obtains from a patient, the more likely they are to zero in on necessary programming changes. One important point to note is that this study evaluated gain preferences only. Most hearing instruments have several adjustable parameters, and some new users might respond as favorably to increased compression ratios or lowered compression kneepoints, thereby reducing louder sounds but maintaining gain for low to moderate level sounds.
Because it appears that the acclimatization process may continue beyond a year, follow-up care after the initial trial period should be planned accordingly. It may be appropriate to schedule check-ups at 4-months, 8-months and 12-months post-fitting. This way, final target settings can be approached systematically for each individual.
References
Bentler, R.A., Niebuhr, D.P., Getta, J.P. & Anderson, C.V. 1993a. Longitudinal study of hearing aid effectiveness. I. Objective measures. Journal of Speech and Hearing Research 36, 808-819.
Bentler, R.A., Niebuhr, D.P., Getta, J.P. & Anderson, C.V. 1993b. Longitudinal study of hearing aid effectiveness. II. Subjective measures. Journal of Speech and Hearing Research 36, 820-831.
Cox, R.M. & Alexander, G.C. 1992. Maturation of hearing aid benefit: Objective and subjective measurements. Ear and Hearing, 13, 131-141.
Cox, R.M. & Alexander, G.C. 1995. The Abbreviated Profile of Hearing Aid Benefit (APHAB). Ear and Hearing, 16, 176- 186.
Cox, R.M., Alexander, G.C., Taylor, I.M. & Gray, G.A. 1997. The contour test of loudness perception. Ear and Hearing, 18, 388-400.
Gatehouse, S. 1992. The time course and magnitude of perceptual acclimatization to frequency responses: Evidence from monaural fitting of hearing aids. Journal of the Acoustical Society of America 92, 1258-1268.
Hornsby, B.W. & Ricketts, T.A. 2003. The effects of hearing loss on the contribution of high- and low-frequency speech information to speech understanding. Journal of the Acoustical Society of America, 113(3), 1706-1717.
Horwitz, A.R. & Turner, C.W. 1997. The time course of hearing aid benefit. Ear and Hearing, 18, 1-11.
Keidser, G., Dillon, H., & Byrne, D. 1998. The change in overall level, spectral shape and loudness perception of speech produced with different vocal effort. Australian Journal of Audiology, 44, 656-670.
Keidser, G., O'Brien, A., Carter, L., McLelland, M., & Yeend, I. (2008). Variation in preferred gain with experience for hearing aid users. International Journal of Audiology, 47, 621-635.
Marriage, J., Moore, B.C. & Alcantara, J.I. 2004. comparison of three procedures for initial fitting of compression hearing aids. III. Inexperienced versus experienced users. International Journal of Audiology, 43, 198-210.
Munro, K.J. & Lutman, M.E. 2003. The effect of speech presentation level on measurement of auditory acclimatization to amplified speech. Journal of the Acoustical Society of America, 114, 484-495.
Olsen, S.O., Rasmussen, A.N., Nielsen, L.H. & Borgkvist, B.V. 1999. Loudness perception is influenced by long-term hearing aid use. Audiology, 38, 202-205.
Ovegard, A., Lundberg, G., Hagerman, B., Gabrielsson, A., Bengtsson, M. 1997. Sound quality judgment during acclimatization of hearing aid. Scandanavian Audiology, 26, 43-51.
Palmer, C.V., Nelson, C.T. & Lindley, G.A. 1998. The functionally and physiologically plastic adult auditory system. Journal of the Acoustical Society of America, 103, 1705-1721.
Philibert, B., Collet, L., Vesson, J.F. & Veuillet, E. 2002. Intensity-related performances are modified by long-term hearing aid use: A functional plasticity? Hearing Research, 165, 142-151.
Philibert, B., Collet, L., Vesson, J.F. & Veuillet, E. 2005. The auditory acclimatization effect in sensorineural hearing-impaired listeners: Evidence for functional plasticity. Hearing Research, 205, 131-142.
Smeds, K., Keidser, G., Zakis, J., Dillon, H., Leijon, A. 2006a. Preferred overall loudness. I. Sound field presentation in the laboratory. International Journal of Audiology, 45, 12-25.
Smeds, K., Keidser, G., Zakis, J., Dillon, H., Leijon, A. 2006b. Preferred overall loudness. II. Listening through hearing aids in field and laboratory tests. International Journal of Audiology, 45, 12-25.
Turner, C.W. & Henry, B.A. 2002. Benefits of amplification for speech recognition in background noise. Journal of the Acoustical Society of America, 112, 1675-1680.
Willott, J.F. 1996. Physiological plasticity in the auditory system and its possible relevance to hearing aid use, deprivation effects, and acclimatization. Ear and Hearing, 17, 66S-77S.
Posted by Jason Galster on Tue, Jun 08, 2010 @ 04:15 PM
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.