Applying the Hearing Aid Fitting Standard to Selection for Adults

Abstract

The recent hearing aid fitting standard for adults outlines the minimum practice for audiologists fitting adult patients with hearing loss. This article focuses on three items of the standard (5, 6, and 7), which focus on the selection of unilateral/bilateral hearing aids, hearing aid style, and coupling, in addition to feature selection. The standard emphasizes that decisions around these three aspects should be recommended for a patient in an individualized manner, based on their needs assessment. For these decisions, the needs assessment might include measures of speech-in-noise ability, social network size, patient preference, and a trial period. Additional elements could include assessments of manual dexterity, binaural interference, and attitude toward hearing aids. However, there are a multitude of ways to practice clinically and still meet the items outlined in the standard. As long as the selection decisions consider individualized patient factors and are capable of meeting validated prescriptive targets, a clinician would be meeting the adult hearing aid fitting minimum standard guidance. In addition, despite the large number of past studies supporting these standards, additional, high-quality research including randomized, controlled, clinical trials are still needed to further support appropriate minimum standard recommendations.

STANDARDS DISCUSSED

• 5. Fitting of bilateral hearing aids is the recommended protocol if the patient is a candidate for hearing aids in both ears and it is supported by the needs assessment.

• 6. The hearing aid style and the ear coupling are chosen to be appropriate for the degree and configuration of the hearing loss. Style and coupling should reflect any physical limitations of the patient. Patient input regarding acceptable styles is taken into account.

• 7. The recommended hearing aids include signal processing and features that support the patient's listening needs. They have the appropriate gain and output, including reserve gain, to meet frequency-specific fitting targets as defined by a validated prescriptive method.

The Audiology Practice Standards Organization (APSO) recently published the first hearing aid fitting standard for adults available in clinical audiology. The standard, developed by a team of subject matter experts, verified by a panel of other experts in the field, and revised based on public feedback, was published on May 2, 2021. Available here ( https://www.audiologystandards.org/standards ), the standard outlines the minimum requirements for hearing aid fittings for adult patients in clinics in the United States. However, the standard itself, consisting of only 15 items, is densely packed with details about the recommended minimums for clinical practice. The focus of this article is on three standard items related to selection, specifically the fitting of unilateral versus bilateral hearing aids (item no. 5), hearing aid style and coupling (item no. 6), and features and processing (item no. 7). Below, some relevant literature related to these selection decisions is reviewed and example applications of the standard to clinical practice are provided. Note that these are not the only ways to follow the standard nor does this represent a comprehensive protocol for making selection decisions. Interested readers seeking more comprehensive coverage of hearing aid selection decisions are referred elsewhere. ^{1 2}

UNILATERAL VERSUS BILATERAL FITTING

Standard item no. 5 states, “Fitting of bilateral hearing aids is the recommended protocol if the patient is a candidate for hearing aids in both ears and it is supported by the needs assessment” (page 1).

Applying the Standard in Practice

The recommendation for bilateral fitting is supported by decades of research demonstrating laboratory benefits of two hearing aids for people with bilateral hearing loss. These benefits include, but are not limited to, better sound quality, localization, and speech recognition abilities with two hearing aids. ^{3 4 5 6 7} In addition, bilateral hearing aids are very common in the United States. Yet, not all real-world evidence supports bilateral fittings. ⁸ Even for patients with generally symmetrical, sensorineural hearing loss, estimates of preference for a bilateral fitting are quite variable; some investigators report most people prefer for bilateral fittings (e.g., 90–93%), ^{3 9} while others note a slight majority prefer bilateral fitting, ^{6 10 11} and still others report only a minority of people prefer bilateral fittings (e.g., 32–39%). ^{9 12 13} These data and discrepant findings highlight the inter-patient variability in preference for bilateral fitting. Reasons for preferring a single hearing aid could include cosmetics, financial, perceived benefit, or loudness comfort. ^{6 10 14 15}

Thus, this decision is based on individual patient tradeoffs. On the one hand, bilateral fittings reduce the risk of auditory deprivation, ¹⁶ offer potential communication benefits, and are preferred by many people (as reviewed earlier). On the other hand, the addition of a second hearing aid comes with additional cost, hassle, and potential stigma. For some patients, the decision is relatively straightforward because the trade-off weighs heavily in favor of one option or the other. For example, for someone with limited useable hearing in one ear (e.g., profound, sensorineural hearing loss and poor word recognition performance), a unilateral fitting would be preferred because the noted laboratory benefits of bilateral fittings would be difficult to realize. Similarly, if a patient has a medical contraindication in one ear, for example, a chronic, active infection, a unilateral hearing aid would be the best recommendation.

For other patients, especially those with generally symmetrical, bilateral hearing loss, the standard recommends bilateral hearing aid fitting, unless contraindicated by a needs assessment. Given the evidence that not everyone with a bilateral hearing loss will prefer a bilateral fitting, the strategy of fitting everyone with bilateral hearing aids, without consideration of a needs assessment, would not result in all patients being satisfied. ¹⁰ Thus, a needs assessment may improve the accuracy of the recommendation for bilateral hearing aids. However, many of the pre-fitting, patient-related factors that might be in a needs assessment do not successfully predict bilateral preference, including age or gender, ^{11 13} personality, ¹⁰ manual dexterity, ¹¹ or other social factors. ¹⁷ Interestingly, although one might expect people with more hearing loss to be more likely to prefer bilateral fitting, degree of hearing loss has been repeatedly shown to be unrelated to preferences for fittings in real-world settings. ^{9 10 11 13 17 18} The evidence indicates these components of a needs assessment are not as useful as one might expect for determining bilateral hearing aid candidacy.

However, there are two items that could be determined as part of a needs assessment that have been somewhat successful in predicting preference. First, some investigators have suggested that preference for a bilateral fitting based on hearing thresholds might be possible if degree of hearing loss is stratified, where people with pure-tone average thresholds greater than 40 dB HL might be more likely to prefer a bilateral fitting. ^{7 19} Second, several authors have suggested that a contraindication of a bilateral fitting is the presence of “binaural interference,” a term used to describe the phenomenon of speech recognition performance that declines with the addition of the second ear. Binaural interferences as a contraindication for a bilateral fitting is supported by case studies ^{20 21 22} and research studies. ^{10 18} However, even with a test battery that captures binaural interference, Cox et al ¹⁰ could only predict preference with 66% accuracy. Thus, although a binaural interference task could be included in the needs assessment for the purpose of identifying those who would be most likely to prefer a unilateral hearing aid fitting, caution is warranted when basing recommendations on the tests, due to the relatively low predictive ability of such a strategy.

The difficulty identifying pre-fitting factors that predict preference for bilateral hearing aid use has led some authors, including Cox and colleagues, to recommend utilizing the trial period to determine whether or not a bilateral fitting is most appropriate. This strategy, too, comes with risks, primarily of additional time and resources with clinic visits or follow-up care. On the other hand, trial periods allow patients to try their hearing aids in real-world situations that are important to them; these situations are difficult to simulate in laboratory or clinic settings. Trying hearing aids in a variety of listening settings is important because bilateral benefits vary considerably depending on the situation, with more bilateral benefits noted in noisy or complex environments ^{6 12 15} and unilateral hearing aids preferred in simple, quiet environments ¹² or in loud sounds. ^{3 10 17}

Because bilateral benefits can be situation-and person-specific, trial periods allow patients to fully explore their interactions with their typical auditory environments and identify for themselves which type of fitting they prefer. However, the order in which hearing aids are provided, sequentially or simultaneously, affects ultimate preference. About 33% of people, when given the chance during a field trial, switch from unilateral to more regular bilateral hearing aid use, whereas only 12% switch from bilateral hearing aid use to more regular unilateral use. ^{6 17} Furthermore, the addition of the second hearing aid reduced hearing aid usage for most participants. ²³ Thus, starting with a bilateral fitting, yet being open to transition to a unilateral fitting, is considered a good strategy for people without clear contraindications for bilateral fitting.

Case Studies

There are at least two ways to implement the standard's recommendation of bilateral fitting when supported by a needs assessment. A clinician could recommend bilateral fittings for all patients without clear contraindications (e.g., financial concern, medical contraindication, limited useable hearing, binaural interference, pure-tone average thresholds better than 40 dB HL). Another strategy would be to fit patients without contraindications bilaterally, but encourage exploration of unilateral fitting as a possibility during a trial period. Discussion of patient preference would be handled at follow-up visits. Both of these strategies are consistent with standard item no. 5.

Fig. 1 displays audiograms for two patients, Gunther and Rachel, who could both be candidates for bilateral hearing aids. Gunther (left panel of Fig. 1 ) is living on a fixed income with no family living nearby. He exhibits symmetrical, rising sensorineural hearing loss, with word recognition scores of 78% bilaterally. Gunther proceeds with a bilateral fitting initially; however, he returns to the clinic for follow-up and reports only using the right hearing aid. During the trial period, Gunther noted his own voice seemed loud and hollow when he used both hearing aids.

Figure 1.

Audiograms for example cases related to decision to fit bilateral hearing aids (standard item no. 5). Circles and red color indicate right ear; x's and blue color indicate left ear.

Rachel (right panel of Fig. 1 ) is an elementary school teacher and exhibits an asymmetrical, sensorineural hearing loss with good (84%) and poor (62%) word recognition scores in her left and right ears, respectively. Historically, only a unilateral hearing aid might be recommended (e.g., see recommendations in the study by Dillon ²⁴ ) because of the asymmetrical nature of her audiogram and word recognition scores. However, a needs assessment revealed she is really struggling to hear in the fourth grade classroom where she teaches. She wants to be able to understand her students and localize their voices, if possible. As a result, Rachel is fit with two hearing aids, and alternated between using the left hearing aid, the right hearing aid, and both hearing aids during her trial period. She reported a strong preference for the bilateral fitting, especially during the school week because she felt like she could monitor and understand her students better with both hearing aids. She ultimately kept both hearing aids and was very satisfied. Making assumptions in either case, with no trial period, would have resulted in dissatisfaction. Audiologists may consider extending trial periods beyond standard durations in some cases to allow the patient to truly experience bilateral and unilateral with either ear. Manufacturers are often accommodating about invoice payment with extended trials.

HEARING AID STYLE AND COUPLING

Standard item no. 6 states, “The hearing aid style and the ear coupling are chosen to be appropriate for the degree and configuration of the hearing loss. Style and coupling should reflect any physical limitations of the patient. Patient input regarding acceptable styles is taken into account” (page 1).

Applying the Standard in Practice

According to the most recent MarkeTrak survey, the most popular style of hearing aids currently is behind-the-ear (BTE), with approximately 75% of hearing aid users reporting BTE use, the majority of which were receiver-in-the-canal (RIC) style hearing aids. ²⁵ Among these RIC instruments, non-custom ear tips are commonly applied, many of which (40–70%) will be open fittings. ^{26 27} The popularity of these instruments is not surprising, given the noted benefits of open canal coupling, including reduced occlusion effect, cosmetic appeal, patient satisfaction, and same-day fitting possibilities. ^{28 29 30 31 32 33} Although these style and coupling options are popular and have benefits for many patients over alternative options, they are not appropriate for all patients. Indeed, some patients will benefit from RIC devices that implement custom ear tips (commonly referred to as an encased receiver) to aid in retention and consistency of coupling. ¹ Like selecting bilateral amplification, style and coupling decisions all require trade-offs and these trade-offs are patient, device, and situation specific. Standard item no. 6 captures three patient-specific factors that can affect style and coupling decisions: (1) audiometric information, (2) physical limitations, and (3) patient preference.

A patient's audiometric profile can affect their eligibility for hearing aid style and also coupling. Each manufacturer has recommendations for the fitting range of a particular instrument and style. Moreover, style considerations need to balance achieving adequate gain with power consumption and availability of features. For example, it would be difficult to fit a small hearing aid, which allows for a full day of wireless streaming, for a patient with severe, sensorineural hearing loss. Currently, power consumption limitations require balancing these needs.

The audiogram is a prime candidate for providing information about open canal candidacy, which allows patients with good low-frequency hearing thresholds to be fit with maximal venting and reduced occlusion effect. ^{28 34} An “open canal” fitting could be accomplished with a non-custom, non-occluding ear tip or with a custom earmold with considerable venting. However, some occluding, non-custom ear tips can also result in “open canal” fittings with significant venting, depending on the shape of a patient's ear canal and how the ear tip fits in it. ³⁵ Despite the benefits, there is a trade-off for open fittings. With more venting in a fitting, the trade-off for open fitting, especially as degree of hearing loss increases, there is potential for insufficient gain, ³⁶ which can result in reduced speech recognition and poorer hearing aid outcomes, ^{37 38 39} or increased risk of feedback due to re-amplification of sound leaking out of the ear canal. Audible feedback can have negative consequences, including reduced hearing aid satisfaction, ⁴⁰ hearing aid non-adoption, ^{41 42} interference with relationships, ⁴³ and hearing aid–related stigma. ¹

Fortunately, feedback reduction systems via digital signal processing are available and used widely in modern hearing aids. ⁴⁴ With feedback reduction system active in an open canal fitting, maximum stable gain on average is approximately 25 to 35 dB, across manufacturers. ⁴⁵ These results led to recommendations that open fittings are possible for losses up to 70 dB HL in the mid and high frequencies. ²⁹

However, this recommendation does not consider the large inter-patient variability noted in maximum stable gain. ^{45 46 47 48} For example, Marcrum et al ⁴⁵ reported there were some adults whose maximum stable gain with an open fitting was over 45 dB with several different hearing aid brands, yet other adults had maximum stable gain that never reached 25 dB, regardless of the brand. Within the context of a validated prescriptive target, 25 dB would be appropriate for approximately 50 dB HL thresholds, not 70 dB HL suggested by Winkler and colleagues. ²⁹ Marcrum and colleagues speculated that individual ear canal geometry, in addition to the type of feedback reduction system implemented by the manufacturer, interacted to limit open-fitting range for some people with all of the hearing aid models tested. Therefore, although a 70-dB HL limit is a reasonable approximation, a clinician should be prepared for the possibility that a person's ear canal geometry allows for significantly more (or significantly less) stable gain.

Ear canal geometry is just one of the physical limitations that needs to be considered during selection of style and coupling. For example, a missing or malformed pinna can limit the feasibility of a BTE fitting. Similarly, because BTE insertion/removal involves two separate manual processes, ²⁷ manual dexterity can be a limiting factor in BTE fittings. ^{30 49} Not all physical contraindications are immediately apparent. For example, a patient might be a hat and glasses wearer, but said presents to clinic hatless and with contact lenses for the purpose of dressing more formally for their professional appointment. It is incumbent on the clinician to explore, formally or informally, physical features that reduce the feasibility of BTE hearing aids. Of course, there are contraindications to ITE instruments as well. Deep fitting completely-in-the canal (CIC) instruments can be uncomfortable. In addition, with mandibular movement (e.g., while talking or chewing), ear canal variations in size and shape are natural, and variable across people. ⁵⁰ For some people, especially those with highly mobile ear canals, a hard ear tip or ear shell at the point of constriction might be uncomfortable and lead to disuse.

Importantly, to be successful and satisfied with a hearing aid fitting, a patient needs to have good hearing aid handling skills. ^{51 52} Fitting a patient with a style or coupling option that is associated with many subjective benefits, such as comfort and quality with open canal fitting, will not help a patient who cannot manage to insert or remove the hearing aids properly. Hearing aid handling issues, especially insertion/removal, have been linked to reduced hearing aid use ⁵³ and hearing aid returns. ⁵⁴ It is important the benefits of open canal or BTE hearing aids are weighed against the physical capabilities of a patient, including the sometimes hidden limitation of ear canal geometry, to maximize the chances of hearing aid success.

Finally, patient input is critical for the style, and somewhat for coupling, decisions. There is ample evidence that if a patient has negative feelings about hearing aids in general, or about a recommended style specifically, that patient will be less likely to be a successful hearing aid user. ^{55 56} If a patient feels more positively about one style over another style, it is prudent to follow the patient's suggestion, assuming it is appropriate for their degree and configuration of hearing loss. Fitting them instead, with what is popular or easy for the clinic, could negatively affect their attitudes toward the hearing aid, reducing both satisfaction and use.

Where does the information to help determine style and coupling recommendations come from? The audiometric profile results from comprehensive diagnostic testing, which is item no. 1 of the adult hearing aid fitting standard (see Messersmith and Benson, this issue). The preceding review reveals that additional information is necessary, however, for selecting hearing aid style and coupling. There are some validated questionnaires that could be used clinically, such as the Three-Clinic Hearing Aid Selection Profile (HASP), ⁵⁴ a 40-item scale which tackles a range of issues related to selection in a standardized way, including a patient's motivation, expectations, attitudes toward cost of goods and services, cosmetic concerns, attitudes about technology, physical function/limitations, communication needs, and lifestyle. Scores on the HASP, especially the manual dexterity and motivation subscales, have been related to return for credit rates, ⁵⁷ suggesting the tool might be a good predictor of hearing aid returns and also demonstrating the importance of hearing aid handling skills for hearing aid success.

However, the HASP is quite long for routine clinical use. Fortunately, a shortened, nine-item version of the HASP, the Characteristics of Amplification Tool (COAT), ⁵⁸ exists. The COAT addresses cosmetic concerns, attitude toward cost, attitudes toward technology, manual dexterity, and lifestyle. This shorter version still assesses many important factors beyond the diagnostic test results. It even includes pictures of a variety of hearing aid styles and allows patients to select which style they would not be willing to use, providing insight into a patient's preferences and willingness to try different hearing aids.

Outside of the HASP or the COAT, there are some measures that address specific factors in isolation, such as manual dexterity tests (e.g., Purdue Pegboard Test ⁵⁹ ), hearing aid expectations (e.g., Expected Consequences of Hearing Aid Ownership ⁶⁰ ), or attitudes toward hearing aids. ⁶¹ These factors could also be determined through careful case history and interviewing. Regardless of how this information is acquired, however, it is vital to determine patient-specific candidacy for style and coupling to balance the benefits and risks of fitting the most popular style and coupling combination for patients.

Importantly, the selection progress can, and should, be ongoing. A trial period could reveal previously unidentified contraindications to the selected style and coupling, in which case the selection should be reevaluated to maximize the chance of success. Again, the reevaluation could be informal, for example, by asking a patient to report if their hat use interferes with their BTE or if a deep fitting CIC is uncomfortable. However, there are also standardized methods for addressing these issues. For example, the Satisfaction with Amplification in Daily Life (SADL) ⁶² addresses positive effects, service and cost, negative features, and personal image. If a patient exhibits poor SADL scores, it is worth revisiting the reasons for those scores and reconsidering the selection. Specific to hearing aid handling, there are also standardized questionnaires available, such as Hearing Aid Skills and Knowledge Inventory (HASKI) ⁶³ and skills-based assessments, such as the Practical Hearing Aid Skills Test (PHAST), ⁶⁴ both of which could identify difficulty manipulating the hearing aids related to style choice. Standardized methods like these are sometimes preferred because relying on self-report for hearing aid management skills can be problematic. Specifically, some patients are confident in their abilities to manipulate hearing aids, but are not technically proficient at hearing aid management. ^{64 65}

Case Studies

In summary, selecting style and coupling choices for a hearing aid fitting needs to incorporate patient-related factors, including the audiometric profile, physical limitations, and patient preference. The selection process might be iterative, with a trial period potentially revealing contraindications to a chosen hearing aid. These next two cases, with similar audiometric profiles, demonstrate how the patient-specific factors affect the trade-off balance for particular style and coupling.

Rebecca (left panel of Fig. 2 ) is a 56-year-old business executive. She has good manual dexterity, is motivated to try hearing aids, wants wireless streaming capability, and is somewhat concerned about cosmetics (although she works in a very supportive environment). Her test results reveal she is a good candidate for open canal, BTE hearing aids bilaterally. She was fit with non-custom, non-occluding ear tips initially. However, during the trial period, she reported that the ear tips were uncomfortable. Visual inspect revealed she has small, elliptically shaped ear canals. As a result, her audiologist changed the ear tip to be a custom mold (slim tip with hollow cavity) and maximum venting. Her fitting was re-verified and the occlusion effect was measured to ensure the fitting was still meeting prescriptive targets and the fitting was non-occluding. This example illustrates how an audiologist might need to make adjustments during the trial period based on an individual's physicality, while maintaining and verifying appropriate venting.

Figure 2.

Audiograms for example cases related to style and coupling selections (standard item no. 5). Circles and red color indicate right ear; x's and blue color indicate left ear.

Ted (right panel of Fig. 2 ) is a 50-year-old male with a long career in sports. Ted's pure tone audiogram is identical to Rebecca's. He is very motivated to pursue hearing aids. His word recognition scores are 92% in both ears and his loudness discomfort levels (LDLs) are 110 dB in both ears for a 3,000-Hz pulsed tone. However, he mentions his hands have never recovered from an old sports injury and he thinks he has the beginnings of arthritis in both hands. His Purdue Pegboard Test results suggest he has borderline difficulty with fine motor control. When presented with the options, he chooses bilateral RIC hearing aids. After the trial period, he reported hating the fact that his hearing aids go behind his ears. At his second follow-up appointment, he reveals he usually wears a hat and sunglasses while working outside. As a result of these three factors (hat, sunglasses, some manual dexterity difficulties), he returned his RIC hearing aids and is fit instead with a pair of deeply seated half-shell, custom hearing aids. The aperture of the hearing aid is into the bony portion of the ear canal, which should reduce the occlusion effect. A recessed faceplate also cuts down on wind noise while he is working outside. Even though they are small, Ted finds he can insert and remove the hearing aids with practice. Further, selecting devices with wireless charging and training him to control the instruments with a cell phone app provides a good experience, despite his dexterity limitations. This example highlights the utility of using a manual dexterity test to evaluate hearing aid style candidacy and modifying the selection based on a patient's physical limitations.

HEARING AID PROCESSING

Standard item no. 7 states, “The recommended hearing aids include signal processing and features that support the patient's listening needs. They have the appropriate gain and output, including reserve gain, to meet frequency-specific fitting targets as defined by a validated prescriptive method” (page 2).

Applying the Standard in Practice

This standard item focuses on the selection and fitting of hearing aid signal processing, including gain and special features. The standard is based, among other things, on decades of research into benefits (e.g., on speech recognition, subjective hearing aid benefit, sound quality ratings) of input-specific gain configuration as specified by prescriptive fitting methods, ^{38 66 67 68 69} digital noise reduction, ^{70 71 72 73} unilateral beamforming, ^{5 74 75} bilateral beamformer microphones, ^{76 77 78} and frequency lowering. ^{79 80 81 82} Although these features and signal processing strategies have documented benefits, it is noteworthy the benefits can be small and person-specific. ^{66 75 79}

Therefore, the recommendation of hearing aid signal processing and features should be patient-specific, taking into account a patient's situation, recognizing that some recommendations can conflict with each other. For example, the magnitude of venting can affect the magnitude of signal-to-noise ratio (SNR) improvements associated with unilateral and bilateral beamforming technologies. With more venting, there is more direct sound in the ear canal, and noise cleaning algorithms including directional microphones are less effective. ^{83 84} Similarly, different gain considerations are necessary with wireless streaming with open canal fittings, relative to fittings with less venting as we alluded to in the example fitting of Rebecca. With large vents, direct sound from the environment will enter the ear canal and the low-frequency streamed signal from the hearing aids will leak out greatly reducing the signal level; the combined effect will likely be less benefit and poorer sound quality for wireless streaming. ⁸⁵ Thus, the recommendations need to be holistic, considering all patient-specific factors identified in a needs assessment that could affect outcomes.

How can these recommendations be made? A needs assessment for features or gain could come from an audiogram, unaided speech-in-noise testing, and patient-reported lifestyle and communication needs. First, audiograms can be used to predict eligibility for some features, most notably frequency lowering, where benefits are more likely for people with steep-sloping, high-frequency hearing loss than for other configurations or more moderate hearing loss. ⁸² As reviewed earlier, the audiogram can also affect style and coupling choices, which will help determine patient candidacy for some noise cleaning technologies. For example, a bilateral fitting is necessary to recommend bilateral beamformers. Similarly, CIC instruments might not offer enough physical space on the faceplate to allow for directional microphones, and this style provides some directionality naturally as a result of the microphone location. ⁸⁶

Speech-in-noise testing can complement the audiogram to provide insight into a patient's abilities in this more challenging situation. Such measures have been advocated to support microphone technology recommendations, with people who exhibit poorer abilities in the clinic being perceived as better candidates for more aggressive noise cleaning technologies. ^{1 87 88} However, such performance abilities need to be interpreted in the context of a patient's lifestyle and routine communication environments. Although most listening situations for older adults have favorable SNRs, where noise cleaning technologies such as digital noise reduction or beamforming microphones would not be expected to benefit a patient, some listeners are in acoustically unfavorable situations where listening can be very difficult (e.g., negative SNR with noise levels > 70 dB SPL ⁸⁹ ). Thus, the listening environments of patients can help select noise cleaning algorithms. One way to measure expected listening demand might be to measure social network size (e.g., Social Network Index ⁹⁰ ). Using a combination of dosimetry and personal diary entries, Wu, Bentler ⁹¹ reported size of social network was a good predictor of listening demand, more so than age alone. As size of network increased, so did listening demand.

Case Studies

In summary, audiometric information, which is critical for generating prescriptive targets, can also be instructive in the selection of features. Other useful elements of a needs assessment could include speech-in-noise testing and information about social network size. The following two cases highlight the importance of using audiometric data and a needs assessment for making patient-specific recommendations for hearing aid features.

Sam (left panel of Fig. 3 ) is a bartender at a local sports bar. He regularly has brief conversations with patrons; sometimes the bar is quiet and sometimes it is very noisy. In addition to his job, with high communication demands, Sam scores high on the Social Network Index, revealing his social network is large and so, too, are his auditory demands. His word recognition scores are good (80% bilaterally), but he reports considerable difficulty in noisy situations (confirmed with an SNR-loss score on the Quick-SIN of 8.5 dB indicating a “moderate loss” ⁸⁸ ). His manual dexterity is excellent and his audiologist helps him select bilateral RIC instruments with non-custom, dome ear tips with limited venting. The dome allows for some slit leak venting (limiting occlusion effect), while avoiding too much venting, which enables beamforming processing across the low and high frequencies. As a result of the specific patient and instrument factors (BTE, low-frequency hearing loss, noisy lifestyle, moderate SNR loss), Sam is also a good candidate for aggressive noise cleaning, including bilateral beamforming microphones, which are easily accessible through a smartphone application.

Figure 3.

Audiograms for example cases related to decision to hearing aid feature and signal processing selection (standard item no. 7). Circles and red color indicate right ear; x's and blue color indicate left ear.

Diane's audiogram is displayed on the right panel of Fig. 3 . Diane's word recognition scores are excellent (100%) bilaterally and her QuickSIN ⁸⁸ scores reveal SNR losses in the normal range (+1 dB bilaterally through headphones). Diane reports great difficulty understanding speech in her job and that she has a very active social life. However, the QuickSIN results suggest her needs are mainly related to improving audibility rather than sound cleaning such as beamforming. Therefore, her audiologist helps her select bilateral mini-RICs with non-custom, non-occluding ear tips. As a result of this combination of factors (significant venting, good speech in noise abilities, steeply sloping audiometric configuration, reported difficulty hearing), Diane is a good candidate for nonlinear frequency compression, assuming they are verified to improve audibility but do not introduce distortion audible to Diane.

CONCLUSIONS

The hearing aid fitting standard for adults describes the minimum procedures that should be applied for appropriate clinical practice. This article addresses three items of the standard (5, 6, and 7), which focus on the selection of unilateral/bilateral hearing aids, hearing aid style, and coupling, in addition to feature selection. The standard emphasizes individualized, patient-centered care, where the hearing aid selection recommendations holistically consider elements of a diagnostic test battery and a needs assessment. The preceding also reviewed evidence supporting the need for considering selection trade-offs in a patient-centered context. For example, despite the popularity and wide-spread use of open-fit, bilateral mini-BTE instruments, these are not appropriate for everyone and do not always lead to optimal benefits with all features. Some of the specific factors that might affect a selection decision include patient feedback from a trial period, audiometric profile, physical limitations, and social network size. Importantly, this article treated each of these decisions as separate, but in clinical practice these decisions will affect each other. For example, the occlusion effect is greater for a bilateral fitting than a unilateral fitting, but only for coupling that is generally occluding. ³³ Moreover, there is evidence that benefits of a bilateral fitting are greater for people with open-fit hearing aids. ³⁰ In addition, bilateral hearing aid and directional microphone benefits are additive; so to maximize the benefits of directional technology, a patient would need bilateral hearing aids. ⁹² This is especially true if a patient is a candidate for bilateral beamforming technology, which has shown significant benefits in the laboratory. ^{76 78} Resolving these complexities requires masterful clinical skill and can be accomplished in any number of ways. Consequently, as long as the selection decisions take into consideration patient factors and are capable of meeting validated prescriptive targets, a clinician can still meet the three selection items in the adult hearing aid fitting standard discussed herein. Additional research is necessary to further support the minimum standard recommendations. Although there are a large number of studies to support the standards, there are few high-quality, randomized controlled, clinical trials upon which to base selection recommendations.