A recent study finds that annoyance ratings for new wearers of digital hearing instruments are equally distributed across intensity and duration. This supports the concept that signal processing algorithms designed to reduce annoyance of noise should not only address stationary noise but also be able to efficiently attenuate transient noises.

Fingernails scraping down a chalkboard. A squealing smoke alarm. A jackhammer pounding through concrete. These are just a few of the images that come to mind when we think of sounds that are annoying. But this is just the tip of the auditory iceberg for new wearers of amplification. Annoyance of sounds comes in many forms and at many different loudness levels.

Presbycusis occurs gradually over time, resulting in progressively less input to the auditory cortex. As the range and intensity of incoming sounds is reduced, the individual’s perception of sound is altered by a commensurate amount. It is reasonable to assume that the longer the auditory stimulation is reduced, the greater the disparity between perception and reality. This same principle would apply to the visual cortex by placing a person in darkness for a prolonged period of time. As their exposure to light is redu

ced, the eyes become increasingly sensitive to it. As light is reintroduced to the eyes, acclimatization takes place and eventually the eyes readapt to the light spectrum. We know that this acclimatization is not nearly so analogous when presenting amplified sounds via hearing instruments to a person with hearing impairment, which makes auditory rehabilitation a considerable challenge.

A primary consideration when reintroducing sounds to the brain via amplification is the individual’s perception and tolerance of real-world sounds. In this sense, we do not necessarily mean “tolerance” of uncomfortably loud sounds, but rather tolerance to unwanted sounds in general. While normalizing speech is of primary interest from a rehabilitative perspective, we must consider that speech is but one of many sounds to which a person with hearing loss will have to reacclimatize through the use of amplification.

A confounding variable is amplified background noise, a necessary byproduct of making speech audible. Considering that better understanding in background noise is the number one improvement sought by hearing instrument wearers,1this should be a primary area of interest for hearing care professionals, manufacturers, and researchers alike. Not only does background noise often reduce speech understanding, but in many cases it creates annoyance, making hearing instrument use an overall unpleasant experience.

Annoyance to noise is subjective—and therefore specific to each individual. Research has shown that new wearers of hearing instruments report that background noise becomes significantly more annoying after being fitted with hearing instruments.2-4 We are assuming that annoyance is similar to aversiveness. These studies have shown that the aversiveness score for the Abbreviated Profile of Hearing Aid Benefit (APHAB)5 becomes worse for the majority of subjects when fitted with hearing instruments.

Recent research by Palmer et al6 was specifically designed to quantify aversiveness and annoyance ratings for a group of moderately hearing-impaired individuals. Their data substantiates the previously cited research that annoyance of sounds is increased for wearers after they are fitted with new hearing instruments. Within the hearing-impaired group there were both new and experienced wearers. The new wearers answered the APHAB pre-test in the unaided condition, and the experienced wearers answered the APHAB wearing their current hearing aids. The aversiveness ratings were significantly worse following the fitting, although these ratings were within the 90th percentile of individuals with normal-hearing. In a separate experiment these authors evaluated hearing aid wearer’s annoyance to two different noise sources on an 11-point scale. These noises were rated significantly more annoying when aided (DNR activated) than when unaided. However, one important fact is that the participants’ annoyance ratings were not significantly different from normal-hearing young adults.

As discussed by Mueller and Powers,7 it is possible that long-term auditory acclimatization may assist the hearing instrument wearer in adapting to environmental noises (some of which are initially perceived as annoying). It is also possible, however, that the annoyance may prompt the wearer to stop using the hearing instruments.8That is, the annoyance level may prevent them from using the hearing instruments long enough to allow acclimatization to occur.

Where Does This Leave Digital Noise Reduction Hearing Aids?
This poses an interesting quandary for the hearing care professional. Traditional thinking has taught us that one goal of the hearing instrument fitting should be to minimize the annoyance level for background noise. However, the research by Palmer et al6strongly suggests that counseling and realistic expectations regarding sound annoyance also must be adequately addressed to better ensure success by the wearer of new amplification.

Though an altruistic goal and a necessary component of auditory rehabilitation, extensive counseling is unfortunately not a universally adopted practice; therefore, technology often is sought to help bridge the gap between reality and wearer expectations. To this end, there is limited research to show that, when digital noise reduction (DNR) technology is properly employed, user benefit regarding background noise is possible.9-12 Further study is needed, however, to understand the type of DNR algorithms needed to address the variety of noise situations in the real world.

In determining how best to reduce annoyance from noise, it is first important to consider the range of noises which the hearing instrument wearers experience in their everyday life. For example, how do these noises vary in intensity and in duration? Referring back to the annoyance ratings reported by Palmer et al,6only two noises were evaluated in that study—traffic and dinner party noise. While it is likely that some noises are amplified to the extent that they really are different from what normal-hearing people perceive, there are little data available describing what types of noises and the variety of noises that are bothersome to hearing aid wearers.

The purpose of the present research was to determine the extent of annoyance from different types of noises, and to assess the types of noises commonly encountered by new hearing instrument wearers.  

Methods
Subjects. Participants (n= 31) were recruited from nine different dispensing clinics. There were no criteria as to audiometric configuration or degree of hearing loss, other than no recent history of middle or inner ear disease. All subjects had bilateral sensorineural hearing loss and were fitted bilaterally. Participants ranged in age from 52 to 81 years old with a mean age of 73.

Hearing aids. All subjects were fitted with wide dynamic range compression (WDRC) hearing instruments ranging in models from completely-in-the-canal (CIC) to behind-the-ear (BTE) devices. The hearing aids were all multichannel, from a variety of manufacturers. The majority of fittings employed directional microphone technology and all utilized digital noise reduction.

Procedures. In general, each clinic was instructed to use their standard protocol when fitting and adjusting the hearing aids. There was one exception, however. Because of the evidence supporting the relationship between hearing aid output and the patient’s loudness discomfort level,13 and the probability that excessive output would influence annoyance ratings, care was taken to ensure that improperly set maximum power output (MPO) levels were not contributing factors in this study. The fitting protocol therefore required that frequency-specific loudness discomfort levels (LDLs) were measured for each subject using the Cox loudness anchors.5 The resulting MPO of the hearing instruments was set accordingly so as not to surpass the wearers’ LDLs. Final settings were verified via 2cc coupler measures incorporating average real-ear to coupler differences (RECD) for each individual.

Following the hearing aid fitting, the new hearing aid wearers were asked to report their listening experiences in their everyday environment. Using a daily diary, the new hearing instrument wearers compiled a list of the noises they experienced during the first week of hearing instrument use, and also rated their annoyance level for these noises. Annoyance was rated on a 0-10 11-point scale (0=not annoying at all; 10=very annoying). The task was not to specifically identify annoying noise, but simply to report all different noises experienced, even the ones that were not annoying.

A panel of five audiology judges, all experienced with real-world noise measurements, rated the different noises. Each noise was rated based on what the judges believed would be the most common intensity (soft, average, or loud) and the typical duration of the noise (transient, medium, or continuous). For ratings of intensity, soft was considered to be any sound less than 55 dB SPL, medium was considered to be any sound between 55-75 dB SPL, and loud was any sound greater than 75 dB SPL. For questionable noises reported by the participants, or those believed to be of borderline intensity, the judges were encouraged to search out similar noises and conduct measurements with sound level meters provided for each judge. Noise was considered transient if it was 1 second or less in duration, medium if it was between 1-2 seconds, and continuous if it was considered to be longer than 2 seconds. The combined judge’s ratings were tallied and the final classifications for intensity and duration were based on a majority rule for each category.

Results
The preliminary analysis of the results involved summarizing the different noises that were reported. As expected, several wearers reported identical or similar noises; however, even after merging the data, over 100 different environmental sounds were identified. Some subjects reported significant annoyance from loud continuous noises (eg, a motorcycle), while others report annoyance from transient duration soft sounds such as computer key strokes. Reported sounds ranged from the expected (clattering dishes, children screaming) to the more obscure (fly buzzing in the room, cat in the litter box), further lending credence to the fact that individual perception is a consideration which must be addressed. Table 1 shows three typical noises reported for each of the nine categories.

The distribution of the ratings for the different environmental noises is shown in Figure 1. Observe that the type of noises experienced were distributed relatively equally throughout the different categories, with very similar distribution for the three duration times summed across loudness levels. While it is often long-duration (or continuous) sounds that are thought to be most annoying, these findings show that 33% of the environmental sounds reported were of transient duration in nature.

As previously mentioned, the part­icipants in this research also rated the annoyance level of the different sounds. This, of course, is an important distinction; if a given environmental sound is not annoying (eg, birds singing), then this sound is of less concern, and it is therefore unlikely that it would discourage hearing instrument use. As shown in Figure 2, there is not a large difference among the different annoyance ratings given for the environmental sounds.

Soft transient sounds are least annoying on average (annoyance level of 4.9). However, annoyance ratings in this category cover an extremely large range from 0 (computer keystrokes) to 10 (second hand on clock). Consequently, the standard deviation of annoyance level is much higher (4.05) than in the other categories (1.14 to 2.51).

As might be expected, the greatest annoyance was for loud continuous sounds. However, even the transient noises were rated as quite bothersome (5.8 averaged across loudness levels), and loud transient sounds were not significantly less annoying than those of medium or long duration. This is interesting in that it lends credence to the notion that sounds of all intensities and duration need to be considered when not only developing, but also when fitting, new technology on individuals with hearing loss.

Summary
Recent research has shown that hearing instrument wearers rate background noise as more annoying than the same noise is rated by normal-hearing listeners.2-4Unfortunately, high annoyance caused by everyday noises may prevent hearing instrument wearers from using their hearing aids. This paper summarizes annoyance ratings for new wearers of digital hearing instruments, which in general, were equally distributed across intensity and duration. This supports the concept that signal processing algorithms designed to reduce annoyance of noise should not only address stationary noise but also be able to efficiently attenuate transient noises.

It is accepted that background noise, in general, is especially annoying to hearing instrument wearers and thus a leading reason why people do not use their hearing instruments—or realize the full benefit from them. This annoyance level is likely increased for new wearers of amplification due to varying degrees of auditory deprivation. While traditional thinking has led us to identify continual background noise (eg, fans, motors, traffic, etc.) as the primary culprit, the subject surveys in this study indicate that annoying environmental noise can be soft or loud, and can have a duration that is short, medium, or continuous.

Most interesting is the finding that one-third of the environmental noises experienced by these subjects are of transient duration, and these sounds were rated essentially as annoying as sounds of medium or continuous duration.

These results indicate that signal processing techniques which only attenuate stationary noise are insufficient for significantly reducing the annoyance of everyday noise. As we continue to develop technology to better address the needs of the hearing-impaired population, it is clear that ongoing research into the perception and real-world experience of the wearer be examined and considered.

References
1.   Kochkin, S. MarkeTrak VI: On the issue of value: Hearing aid benefit, price, satisfaction and brand repurchase rates. The Hearing Review. 2003;10(2):12-25.

2.   Boymans, M., Dreschler, WA. Field trials using a digital hearing aid with active noise reduction and dual-microphone directionality. Audiology. 2000;39,260-268.

3.   Surr R, Walden B, Cord M, Olsen L. Influence of environmental factors on hearing aid microphone preference. J Am Acad Audiol. 2002;13,208-322.

4.   Ricketts T, Henry P, Gnewikow D. Full time directional versus user selectable microphone modes in hearing aids. Ear Hear. 2003;24,424-439.

5.   Cox, RM, Alexander, GC, Taylor, IM, Gray, GA. The Contour Test of loudness perception. Ear Hear. 1997;18: 388-400.

6.   Palmer CV, Bentler RA, Mueller HG. Amplification with digital noise reduction and the perception of annoying and aversive sounds. Trends Amplif. 2006;10:95-104.

7.   Mueller HG, Powers TA. Considerations of auditory acclimatization in the prescriptive fitting of hearing aids. Seminars in Hearing. 2001;22(2):103-124.

8.   Kochkin, S. MarkeTrak VII: Customer satisfaction with hearing Instruments in the digital age. Hear Jour. 2005;58(9): 30-38.

9.   Ricketts, TA, Hornsby, BW. Sound quality measures for speech in noise through a commercial hearing aid implementing digital noise reduction. J Am Acad Audiol. 2005;16(5):270-277.

10. Mueller HG, Weber J, Hornsby BW. The effects of digital noise reduction on the acceptable noise level. Trends Amplif. 2006;10: 83-93.

11. Powers TA, Branda E, Hernandez A, Pool A. Study finds real-world benefit from digital noise reduction. Hear Jour. 2006;59(2): 26-30.

12. Burton P, Smaka C, Powers TA. Digital Noise Reduction: Yes, there is research supporting its effectiveness. The Hearing Review. 2006;13(3):82-87.

13. Mueller HG, Bentler RA. Fitting hearing aids using clinical measures of loudness discomfort levels: an evidence-based review of effectiveness. J Am Acad Audiol. 2005;16(7):461-472

Correspondence can be addressed to HR or August R. Hernandez, 24398 Overlake Lane, Lake Forest, CA 92630; e-mail: [email protected]