Impact of Aging and Cognition on Hearing Assistive Technology Use

Abstract

Many factors go into appropriate recommendation and use of hearing assistive technology (HAT). The aging auditory system presents with its own complications and intricacies; there are many types of age-related hearing loss, and it is possible that the underlying cause of hearing loss can significantly impact the recommendations and performance with HATs. The audiologist should take into consideration peripheral and central auditory function when selecting HATs for the aging adult population as well as when selecting appropriate types of technology including personal sound amplification products, hearing aids, cochlear implants, and other assistive technology. The cognitive ability of the patient plays a central role in the recommendations of HAT. It is possible that the use of HATs could mitigate some of the effects of cognitive decline and thus should be considered as early as possible. Assessment of ability and appropriate recommendations are crucial to consistent use of HAT devices.

Learning Outcomes: As a result of this activity, the participant will be able to (1) describe the impact of aging on the interaction between the peripheral auditory system and the central auditory system, and (2) describe the impact of cognitive ability on HAT recommendations and use.

For most aging adults, histopathological changes within the cochlea result in a sensorineural hearing loss often referred to as presbycusis; the degree of these changes and the resultant hearing loss increase with increasing age.¹ The psychophysical implications of this hearing loss include reduced frequency, intensity, and temporal resolution, which commonly have repercussions on an individual's listening and understanding abilities, increasing the difficulty they experience when listening in various environments. Hearing assistive technologies (HATs) are devices and strategies designed to lessen the impact of the specific challenges associated with hearing impairment and in turn improve quality of life for the user.

With current technology, there are several ways we can deliver a signal to the auditory cortex, each carrying unique considerations when interacting with the aging auditory system. Furthermore, that aging auditory system is housed within an aging individual, which will impact device selection, fitting, and rehabilitative care in ways that are not limited to enhancements to perception of sound. This article will discuss HAT options with respect to unique considerations for an aging adult, the impact of the aging auditory system and the individual on these potential auditory acoustical interventions, and the foundational auditory and technology knowledge necessary to appropriately fit these patients.

The Aging Auditory System

Changes in cochlear histopathology due to age have been classified into four types of presbycusis^{2 3 4}: sensory, neural, metabolic, and mechanical. Sensory presbycusis is the degeneration of hair cells, stereocilia, and supporting cells in the organ of Corti, which typically occurs in a basal-to-apical progression and as a result commonly presents as a high-frequency hearing loss. These degenerative changes usually begin in middle age, but advance slowly; thus, degeneration tends to be limited to the most basal end of the cochlea, with less impact on the cochlear regions encoding that are traditionally considered the speech frequencies. Neural presbycusis refers to hearing loss resulting from the loss of the auditory neuron beyond degeneration within the organ of Corti. Given that the auditory system typically has around 35,000 auditory nerve fibers, the perceptual impact of the loss of neurons may only become apparent across several decades. As such, this type of presbycusis often occurs later in life when the number of functional neurons falls below what is necessary for effective transmission of the signal. Metabolic presbycusis is damage to the stria vascularis and is associated with a characteristic flat hearing loss. If no pathologic correlates can be found in the organ of Corti, auditory neuron, or strial tissue, Schuknecht characterized the hearing loss as mechanical presbycusis.⁴ He postulated that the slowly progressive descending audiometric curve could be caused by an abnormality in the structures involved with the motion of the cochlea, possibly the basilar membrane or the spiral ligament. It should be noted that these changes within the cochlea cannot be characterized in someone who is living, and thus presbycusis is often used generically to describe age-related hearing loss. These changes in histopathology cause the changes in auditory perception associated with aging.

There are three components affecting an older person's ability to accurately perceive the intended auditory signal: audibility, cochlear pathology, and central auditory pathology. First, the signal may not be audible, meaning the sound is not sufficiently intense to cause adequate movement of the auditory structures necessary to excite the system and as a result hear the signal.^{5 6} This reduces access to sound and can cause changes to the perception of the signal. Second, in those with a sensorineural hearing loss, such as presbycusis, a cochlear pathology likely contributes to the hearing loss beyond the audibility of the signal—for example, reduced frequency discrimination^{3 4} and temporal encoding errors.^{7 8 9} Third, the system deficits that can be most difficult to describe are those within the auditory cortex. These are confounded by both changes in the input, as described previously, and also a potential neuronal or cortex-level auditory processing problem contributing to the inability to perceive, decode, and understand the signal.⁷ However, these systems are often dismissed and are not considered during the assessment of auditory function. More than 70 years ago, Karlin noted that traditional audiometric evaluations do not assess behavior in complex listening situations.¹⁰ Despite this assessment, most testing completed by audiologists evaluates audibility and fails to assess the entire auditory system. Furthermore, assessment of the auditory processing system in those with presbycusis, if completed, is confounded by the limitations of many of the tests of auditory processing that require normal audibility. Evaluation of speech understanding in elderly listeners is difficult because speech recognition itself is a complex process. Most models of speech perception maintain similar underlying mechanisms that rely on a central system for cognitive processing of speech^{11 12 13}; therefore, the complete understanding of the auditory system is often left to simply understanding the peripheral auditory system and assuming changes within the central system. However, as discussed in previous articles, adults with a compromised central auditory system may not capitalize on central system redundancies and therefore may not listen effectively. These deficits may be present during comfortable listening situations, but are especially apparent in difficult, noisy listening situations; these are the situations most commonly reported as difficult by patients who seek support from HAT.

Hearing Assistive Technology

HATs are any device that can help an individual interact with the acoustic world more easily. A variety of HATs are available, each with a differing function and fitting criteria. As adults age and face the consequences of presbycusis, it is likely that they would benefit from the use of a HAT. Despite their potential benefits, HATs are underused by older adults and the general population.

Types of HATs

Although HAT includes to a wide variety of technologies, one thing remains consistent: all of them require buy-in from the user for the best use, which will be discussed in depth later. There are a wide variety of assistive technologies available to consumers.

Personal Sound Amplification Products

Although it would likely prevent a lot of misuse, not all HATs require a visit to the audiologist and programming that requires frequency specific information. There are several over-the-counter products available to consumers without the need to visit an audiologist or hearing instrument dispenser. They can take many forms, including looking like a hearing aid or other ear-level device. These devices are described by the U.S. Food and Drug Administration (FDA) as products that are used to amplify sounds for persons who are not hearing impaired; they are not intended to compensate for hearing impairment.¹⁴ For some, such as those with temporary hearing losses or those for whom device loss is a concern, these may be an excellent alternative to hearing aids. Although superficially the function of personal sound amplification products (PSAPs) may appear similar to hearing aids, PSAPs are not regulated under the Food, Drug and Cosmetic Act as they are not intended for those with a hearing impairment. However, the FDA does regulate these devices under a provision of the Radiation Control for Health Safety Act of 1968, which covers products that emit acoustic vibrations.¹⁵ Other examples of devices falling under regulations of the Radiation Control for Health Safety Act include amplified telephones and television devices. Many of these devices are used by both persons with and persons without hearing impairment. Although audiologists often recommend more specifically adjusted devices for their patients, such as hearing aids, PSAPs should be considered for our patients as well, as they may be an appropriate addition to a hearing aid or cochlear implant for some patients and in rare occurrences may serve the needs of a subset of patients.

Hearing Aids

Changes in peripheral and central auditory ability can require the use of hearing aids to provide additional audibility.¹⁶ Significant consideration into style, level of technology, and patient needs should be considered and will be discussed in depth. No hearing aid should be prescribed without appropriate verification and outcome assessment of the treatment. Currently, the most efficient way to verify audibility is through real-ear probe microphone measurements compared with a valid and reliable prescriptive target (e.g., National Acoustics Laboratory method (NAL) or Desired Sensation Level method (DSL)). These measurements are part of recommended fitting guidelines set forth by the professional organizations of audiology.^{17 18 19} In addition to verification, outcome assessment is necessary to ensure that the hearing aid is benefiting the person. This can be completed through a variety of outcome measurements that have been discussed in previous issues of this journal (e.g., May 2013 (Vol. 34, Issue 2); February 2012 (Vol. 33, Issue 1)). It is through verification and outcome assessment of the treatment that audiologists can ensure patients and any reimbursement mechanisms that appropriate care was provided.

Cochlear Implants

When cochlear implants first received approval through the FDA, their use was restricted to those individuals with profound sensorineural hearing loss. Since 1985, the candidacy criteria for cochlear implantation has expanded, in large part due to the highly successful outcomes through use of the device. Current cochlear implant candidacy guidelines include two categories of implantable devices, a traditional cochlear implant and a hybrid cochlear implant. FDA criteria for a traditional cochlear implant includes audiometric thresholds of greater than a moderate to severe sensorineural hearing loss and speech perception scores in the aided condition of poorer than 50% in the ear to be implanted and poorer than 60% in the best aided condition (could be contralateral ear or both ears together). FDA criteria for a hybrid cochlear implant specifies a severe to profound high-frequency hearing loss (threshold average of ≥75-dB hearing loss in the ear to be implanted and ≥60-dB hearing loss in the contralateral ear at the test frequencies of 2,000, 3,000, and 4,000 Hz) and Maryland Consonant-Nucleus-Consonant (CNC) word list, word recognition scores of 10 to 60% in the ear to be implanted and poorer than 80% in the contralateral ear.

Prior to expansion of cochlear implant criteria to include the hybrid device, individuals whose etiology of hearing loss was strictly presbycusis were not commonly candidates for cochlear implantation until much later in life when the degeneration of sensory and neural structures was greatly advanced. Published data suggest, however, that aging adults' performance with a cochlear implant is enhanced if they are implanted at a younger age and with higher preoperative speech scores.^{20 21} There is an even greater delay in implantation for older adults receiving medical insurance coverage through Medicare due to strict cochlear implant candidacy criteria specified by the Center for Medicare and Medicaid Services (CMS). In contrast to the FDA criteria, CMS limits cochlear implantation to those individuals with aided speech perception scores of less than 40% in the ear to be implanted and less than 50% in the best aided condition. Furthermore, at the current time, CMS does not recognize candidacy criteria for the hybrid cochlear implant. As such, individuals receiving medical insurance coverage through Medicare must qualify for a cochlear implant under very restrictive traditional cochlear implant criteria. Due to mounting evidence that better preoperative speech perception enhances potential outcomes for cochlear implant use both in terms of speech perception outcomes and improvements to quality of life,^{22 23} the sentiment of Lin et al is valid: expansion of current CMS cochlear implant criteria to match the current FDA guidelines appears to be necessary to allow older adults to recognize the full potential of a cochlear implant.²⁰ Additional research is necessary to demonstrate the benefits (not just improvements to speech perception) of early implantation and intervention in older adults to support the recommendation for change to CMS cochlear implant criteria.

Additional Assistive and Alerting Devices

Given changes in auditory processing associated with aging, solely providing audibility may not improve a person's hearing ability, thus technology that improves the signal-to-noise ratio may be the best solution. These technologies include a remote microphone that is placed near the signal of interest; the signal is sent directly to the listener through wireless technology and is delivered to the listener through the personal hearing aids or through earphones. By virtue of the microphone location near the signal and the direct transfer of the signal to the listener, these systems enhance the signal-to-noise ratio for the listener. Changes in the auditory system require older adults to have a better signal-to-noise ratio than younger listeners²⁴; thus, devices that improve the signal-to-noise ratio are often beneficial for this population. This is even more so for those with cognitive decline who may not have the ability to attend to complex signals.

Enhanced alerting devices may be necessary for patients with hearing loss. We alert to auditory signals related to our telephone ringing, doorbells, and smoke detectors throughout the day and night. An individual with hearing loss may not hear any of these signals, or an individual who uses HATs may hear these signals during the day when they are wearing their amplification system but not at night when they remove the amplifying devices. Patients who cannot hear alerting devices, such as fire alarms, will not be able to respond to them. We want to ensure that our patients are safe and will be alerted when necessary. Our patients depend on us to ensure their hearing ability for safety, even when they are not wearing their HAT. For patients with cognitive decline who are living alone or in their own homes, we need to discuss alerting issues with their family members and caregivers.

Use of HATs in General Population

Healthy People 2020 has outlined several goals that relate to improving hearing health outcomes for adults. Specifically, the initiative calls for an increase in the number of adults over 70 who use hearing aids and HATs as well as the number of adults age 20 to 70 who have had a hearing evaluation in the past 5 years.²⁵ Currently, HATs are not used by all patients who could benefit from the use of such devices.²⁶ The most commonly cited work assessing HAT usage comes from The Better Hearing Institute and Sergei Kochkin; however, not all types of HATs are assessed in these surveys.²⁷ Specifically, these surveys only investigate the conventional hearing aid market. The reports suggest that for hearing aids, the market penetration is likely between 20 and 25%,^{27 28} constituting ∼8.2 million hearing aid users out of the 33.4 million people with hearing impairment. Some have suggested that of the 33.4 million people with hearing impairment, only half would need amplification²⁷; however, this is still results in only 51.3% of patients with hearing loss using appropriate amplification. Even if this is restricted to individuals over the age of 70 years, it is estimated that 16 million adults in the United States have hearing loss with the usage of HAT being related to the severity of loss.²⁹ Specifically, persons with lesser severity of hearing loss have a much lower usage of HAT (mild hearing loss, ∼3% use of hearing aids). Persons with a greater severity of hearing loss have a much greater usage of HAT (40% for moderate and over 75% for severe hearing loss). Although the usage of HAT for individuals with more severe degrees of hearing loss increases, data suggest that these persons may not be receiving the HAT most appropriate for their hearing loss. For example, with respect to cochlear implantation, over 150,000 of the 16 million adults over 70 years of age with hearing loss likely have a severity of hearing loss that would qualify for traditional cochlear implantation candidacy criteria.³⁰ Despite this, only 58,000 adults (all ages, not just restricted to those over 70 years of age) in the United States have received a cochlear implant as of December 2012.³¹ Thus, even if each of the 58,000 adults who have received a cochlear implant were over the age of 70, which is not the case, that would represent a penetration rate of less than 40%.

Despite reports that adults do see hearing aids as beneficial for those who need them,³² there continues to be low uptake of HAT. It is reasonable to consider that other factors may contribute to the small percentage of individuals with hearing loss who use HAT. Some of these may include residual perception of the hearing aid effect, personal judgments of the use of hearing aids, and unrealistic expectations of performance with the device. For example, results from older studies have suggested a possible hearing aid effect, where viewers judged wearers of hearing aids more poorly on intelligence and social behaviors^{33 34}; other studies have suggested that adults viewing other adults did not demonstrate a hearing aid effect.^{35 36 37} More recent data suggest that the hearing aid effect may have all but disappeared.³⁸ So it is of question why older adults do not consistently pursue HATs when they are clearly needed and when their peers do not appear to judge them critically. Kricos et al reported that 45% of adults had high expectations of hearing aids and their function³²; it is possible that these unrealistically high expectations of aids lead to increased disappointment by those that do pursue them. From these unrealistic expectations, friends and family could influence HAT perception as well. The factors contributing to lower usage of HAT by older adults must be addressed, particularly because there appears to be significant consequences of not treating hearing loss.

A study commissioned by the National Council on Aging reported that adults with hearing loss who do not use hearing aids have higher rates of depression, anxiety, and other psychological/psychosocial disorders than those without hearing loss and thus do not require the use of hearing aids.³⁹ This survey also looked at the positive benefits of using assistive technology and showed that appropriate use of HAT had a positive benefit on quality of life for the user as well as their significant other. This has been further demonstrated in other studies that showed significant decrease in caregiver stress with the use of appropriate amplification.⁴⁰ Mulrow et al demonstrated that those with hearing loss who did not use appropriate amplification had a decrease in social and emotional function including communication ability and cognitive function.⁴¹ A growing body of literature also has shown poorer cognitive performance in older adults presenting with untreated hearing loss.^{42 43 44 45 46 47} More remarkably, two longitudinal studies suggested an association between hearing loss and greater cognitive decline in a 6-year period of follow-up.^{48 49} It is possible that the use of assistive technology could mitigate some of these aging/cognitive effects; however, this has yet to be demonstrated.

In addition to treating hearing loss through the use of hearing aids, referrals for cochlear implantation should be made earlier in the process. The data demonstrating the benefits of early implantation in older adults were already discussed, but to summarize, older adults who are implanted at a younger age and with higher preoperative speech perception scores realize greater benefit from their cochlear implant with respect to postoperative speech perception and quality-of-life scores. The benefits of early implantation may result from the impact of electrical stimulation on the auditory system. Specifically, chronic long-term electrical stimulation has been shown to promote spiral ganglion cell survival with increased cell size and normal cell morphology, which leads to an increased number of surviving auditory neurons and increased spiral ganglion cell density.^{50 51} Spiral ganglion nerve fibers are lost throughout each decade of the aging process, with loss of nerve fibers being more aggressive in certain types of presbycusis (neural). The provision of electrical stimulation through use of a cochlear implant may stop or reduce the loss of neural fibers, which heightens the need to ensure appropriate treatment of hearing loss across the life span.

Although available usage data suggest that hearing aid and cochlear implant uptake is significantly lower than would be expected, the actual uptake of all assistive technologies remains unknown. Despite its high prevalence and consequences on health outcomes, hearing loss is largely underdiagnosed and thus undertreated.⁵² Although recent reports suggest that the negative public perception of HATs (also known as the hearing aid effect⁵³) is declining overall in the younger population,³⁸ there is still a potential negative self-perception of the use of HATs particularly in the older population. In the most recent Marketrak report,⁵⁴ psychosocial stigma ranked 15th in whether a person would pursue hearing assistance in the next 2 years; other factors, such as financial and product issues, were listed as more important. This represents a change from previous data suggesting that the stigma associated with hearing aid use was a prohibitive factor.

The Audiologist's Role in HAT Selection

It remains a problem that many older adults do not pursue diagnosis or treatment for hearing-related problems.⁵⁵ With this knowledge, audiologists take on the task of demonstrating the need and benefit of HATs to patients knowing that they may not routinely use the device if they do not believe they have a significant impairment or that they will not see benefit from such devices.^{30 56} Although the largest motivation for HAT use is patient confidence that communication will improve, the biggest barrier is the perception that hearing loss does not merit correction.⁴³ This is further complicated when someone has cognitive decline, as their ability to understand the diagnosis, treatment, and technology may be reduced.

Anecdotally, the use of HATs for someone with cognitive impairment has been questioned given the possibility of device loss, the inability to report problems/device failure, and the need for assistance with use. These arguments have been strengthened as studies have suggested that although the use of HATs does improve speech perception, there is no compelling evidence that the use of such devices improves cognitive ability.^{57 58} Lin et al suggested that people with hearing loss are more likely to have significant cognitive decline,⁴⁸ and Jorgensen et al suggested that those with unidentified and untreated hearing loss may be at increased risk for being diagnosed with cognitive impairment.⁵⁹ As discussed previously, the risk of depression, anxiety, and other psychological conditions increases as hearing ability decreases.⁶⁰ It is possible that the undiagnosed or untreated hearing loss leads to social isolation, which in turn may lead to other sequela. As many listeners wait years before seeking treatment for hearing loss, the effects of long-term untreated hearing loss may not be easily reversed. As with most diseases and disorders, early identification and intervention of hearing loss leads to the greatest potential for treatment outcomes and the greatest potential reduction in associated sequela.

Treatment of hearing loss in the adult population, however, is an issue of self-driven use. We rely on patients to appropriately use the technology. Overall, there is low use of durable medical equipment by the elderly population.⁶¹ This presents a problem when fitting patients who are not ready for HATs. If a patient is not ready, it is possible that the hearing aids will be unused and will not benefit the patient. This requires buy-in from patients prior to pursuance of the devices. This becomes even more complicated if patients do not have full cognitive capacity. Their buy-in may be present initially, but reduced cognitive capacity may limit potential benefits of the device. For example, an individual may be unable to remember to use the devices and may not understand how to use the devices once they are home. It is currently estimated that ∼70% of individuals with dementia live in the community where family caregivers are responsible for assisting them with daily tasks.^{62 63 64} As a result, the caregiver becomes responsible for the care and use of the HAT device. Although the care of the devices falls on the caregiver, Palmer et al reported reduced caregiver stress when appropriate HATs are used.⁴⁰ Recommending HATs for those with cognitive decline not only improves their lives, but also improves the overall well-being of their caregivers.

It is the responsibility of the audiologist to take into account the patient's ability, needs, and support when selecting appropriate HAT. As discussed previously, there are many options for assistive technology available to patients. For some patients, the best option may be a noncustom, simple amplifier, and for other patients personal hearing aids or cochlear implants may be more appropriate. It is essential that the audiologist use measurements of desire to hear in different situations and need and expectations prior to HAT selection to ensure benefit from the devices. A scale of readiness, such as the one presented by Palmer et al, demonstrated that patients who report more hearing loss are more likely to pursue amplification.⁶⁵ These types of scales/measurements are needed to determine if a patient is ready to pursue a HAT for his or her hearing impairment. Another potential outcome measurement could be the Client Oriented Scale of Improvement,⁶⁶ which could help the audiologist identify the specific needs of the patient and select the appropriate HAT strategy (device, communication strategy, etc.). Targeted interviewing skills are essential to extracting these patient-specific needs. Rather than a more traditional teaching/interview style, a conversational or patient-led discussion may be more appropriate for this population. It is possible that the goals of patients with cognitive decline may be very different than what would be gleaned from a formal interview. It is through the use of outcome measurements and good listening and counseling skills that our patients will feel that they are in control of their environment and the use/selection of their HAT device. This control is essential for long-term motivation for use.^{67 68}

HAT Selection, Fitting, and Beyond

The appropriate selection of HATs is one of the key steps in the process of treating hearing loss. Appropriate selection of HAT should be determined through thorough case history, comprehensive evaluation of audiometric abilities including speech-in-noise testing, and determination of patient needs, abilities, and desires for the device and treatment program. The device selection should include physical/cognitive abilities and limitations, audiometric results, and patient preference. This order ensures that patients are fit with technology that meets their needs.

It is essential to first consider the physical and cognitive limitations of the patient as this is fundamental to the appropriate use of the devices. One should consider not only the placement of the device(s) (e.g., on the ear, on the body, etc.), but also how the patient is going to manipulate controls on the device, if necessary. Physical anomalies, such as lack of pinnae or reduced elasticity of the cartilage of the pinnae, are important considerations; for the elderly population, it is also important to consider physical limitations that could impact HAT use. This could include examinations of physical dexterity, visual ability, and range of motion. Cognitive assessments to ensure device safety through the addition of battery door locks and additions of loss-prevention measures could yield better HAT use. Additional considerations, such as previous HAT use, could mitigate future problems associated with a change in HAT placement on the body (e.g., changing from in-the-ear style hearing aids to behind-the-ear style hearing aids). Taking these into consideration as the first step improves patient outcomes for those with and without cognitive impairment. Although audiometric considerations ensure patients are fit with appropriate technology, they should be considered once other factors related to physical/cognitive ability are taken into account. Selection of audiometrically appropriate technology decreases rates of dissatisfaction due to feedback and fit issues. The audiologist should not only rely on the pure tone behavioral thresholds when determining appropriate HAT; rather, they should rely on other measures of auditory ability such as word recognition ability in quiet and in noise. Once these criteria have been met, any additional patient desires should be taken into consideration.

Beyond selection of the device, implementation of features within the HAT technology may vary with older adults. Within each type of HAT device, it is necessary to consider what features would be appropriate for the patient. Determination of the appropriate features will be guided by the physical/cognitive limitations, audiometric results, and patient preference as previously discussed. Of particular importance for device features is the patient's cognitive limitations. Several studies have suggested that implementation of different features within hearing technology may reduce cognitive load based upon the theory of resource allocation. The premise of resource allocation is that an individual has a limited set of resources at their disposal and that this pool of resources is shared across each sensory input and cognitive demand. If one system, such as audition in the case of an individual with hearing loss, is using a larger portion of the available resources, then there is less of the resource pool available for integration or manipulation of other cognitive demands resulting in such things as longer response times or diminished comprehension. This resource pool may further diminish through aging and cognitive decline.⁶⁹ For example, Lunner and Sundewall-Thorén suggested that cognitive ability could have an impact on the benefit an individual receives from HAT.⁷⁰ They also found a correlation between compression (fast or slow) and score on a cognitive test, specifically that persons with higher cognitive ability performed better in a speech perception task using hearing aid technology with a fast compression onset than did persons with lower cognitive abilities. This result suggests that perhaps the capabilities of the cognitive system dictate whether or not an individual can take advantage of acoustic manipulations like fast-acting compression.

Other features have been suggested to reduce cognitive effort (e.g., see Desjardins and Doherty⁷¹); however, there is currently no truly accurate measurement of cognitive effort, so these studies cannot demonstrate the impact of technology on resource allocation ability directly. There are tactics such as dual-task paradigms that attempt to demonstrate changes in cognitive ability, but different modalities are taxed within these dual tasks. Some authors have suggested that hearing aid features such as directionality, noise reduction, and perhaps frequency lowering can provide benefit that cannot be measured by current auditory tests.⁷² With increased complexity and listening time, these studies do suggest that listening fatigue does have a significant impact on auditory perception. It could be concluded that for adults with untreated hearing impairment, the requirement that they use more attention and cognitive load to perceive the auditory stimuli means that the cognitive system is working harder, and through the use of HATs, the central system has more resources to do other things. As discussed in this and other articles within this issue, those with hearing loss have increased demands on cognitive processes and resources. Many situations require high-level cognitive effort on the part of the listener, such as listening in a restaurant. Due to hearing difficulty, many individuals withdraw from these situations—an effect that increases with more hearing loss.⁷³ A large body of research implies a link from hearing loss to social isolation to cognitive impairment⁶⁰; however, there is little, if any, research to help us understand the interaction between these factors. A better understanding of the cross section of hearing loss, social isolation, and cognitive ability is needed to develop improved rehabilitation strategies.

To date, there has been little research into the specific fitting protocols for older adults using hearing aid technology or cochlear implant technology. However, there have been anecdotal reports of recommended fitting practices for older adults. For example, there has been a longheld belief in cochlear implant clinics that older adults or individuals with cognitive decline perform better with programs that use a slower firing rate as opposed to programs that use a fast firing rate. At the current time, this recommendation is not founded in published research. Rather, when programming cochlear implants, steps should be taken to ensure that electrical dynamic range and electrical stimulation patterns are appropriate for the individual and their unique auditory system. One consideration with older adults is the pattern of neural survival at the level of the spiral ganglion and higher. When stimulating the auditory system electrically, the loudness perception of the electrical signal by the user is directly related to the total neural activity elicited by the signal. Given that older adults may have variation in the pattern of nerve survival along the length of the cochlea, the audiologist should take steps to ensure that the electrode configuration selected (common ground, monopolar, bipolar) will elicit a response from an adequate population of nerve fibers to allow for appropriate loudness perception while also maintaining some degree of region/frequency specificity within the cochlea. For older adults with a hearing loss etiology of presbycusis, the time between onset of hearing loss and receipt of cochlear implant may be quite long and as a result, neural survival may have suffered, particularly for those individuals with neural presbycusis. As such it is possible that this population may require electrode configurations that result in a broader spread of electricity in the cochlea.

As noted earlier, verification of the return of audibility is important no matter what device is being fit.^{74 75} Persons with hearing loss can have difficulty making loudness judgments and sometimes cannot provide accurate, reliable feedback regarding the sound.⁷⁵ Therefore, objective measurements are recommended for verifying the audibility of the signal provided by the amplification device. For those individuals who use a cochlear implant, there is no commonly accepted means for verifying device settings. The Minimum Speech Test Battery for Adult Cochlear Implant Recipients is the currently recommended battery of speech perception tests for use with adult cochlear implant recipients to evaluate and monitor performance with their cochlear implant.⁷⁶ This test battery, however, is a means to assess speech perception and is therefore really an outcome assessment rather than a verification technique. Verification of device function can only be obtained through an objective measure. The most commonly used objective measures of device function in the cochlear implant clinic are electrically evoked compound action potentials (ECAP) and electrically evoked stapedial reflex thresholds (eSRT). Results from a study currently being analyzed by these authors suggest that ECAP measures are more commonly use by cochlear implant audiologists than are eSRT measures. The greater use of ECAP likely stems from the integration of this measure into each of the cochlear implant manufacturer's software. The greater use of Neural Response Telemetry (NRT) measures over eSRT is of concern, however, because ECAP measures have not been shown to be highly predictive of the limits of the electrical dynamic range (threshold or comfort levels), but rather generally fall somewhere within the electrical dynamic range. As such, although ECAP may be useful for approximation of both threshold and comfort levels,⁷⁷ they should not stand alone for accurate approximation of psychophysical loudness judgments due to the weak relationship between ECAP measures and threshold and comfort levels.⁷⁸ At the current time, eSRT measures provide the best estimate of perceived comfortable loudness levels, as the measurement demonstrates a high correlation across all channels with behaviorally measured C/M levels (measures of the upper limit of the electrical dynamic range).^{74 79 80 81 82 83}

Data suggest that early intervention and use of hearing aids have been shown to improve outcomes for people with hearing loss.^{84 85} A large study by the National Council on Aging of adults demonstrated that early hearing aid use increased earnings power by ∼50% and improved general health.⁸⁶ Older adults receiving cochlear implants performed better with the device if they were implanted at a young age and had better speech perception scores preimplant. These data were more compelling in cases of unilateral implantation. For older adults receiving bilateral cochlear implants, the outcomes appear to be more variable.⁸⁷ Noble et al suggested that this variable performance may result from limitations in integration of binaural cues for some older adults.⁸⁷ Older adults using cochlear implants appear to realize greater benefit from the device if they are implanted in the right ear.²¹

Conclusions

The auditory system is highly complex and is exacerbated by the aging process. The interaction of the decline in peripheral and central function associated with aging presents unique challenges. The increased problems associated with dementia and other cognitive impairments further complicate an already arduous task. There are many causes of age-related hearing loss and, although it is not possible to diagnose the type or combination of types of presbycusis when the person is alive, the underlying cause of the hearing loss (i.e., type of presbycusis) will likely significantly impact the treatment plan. The best way to ensure optimal outcomes with an older adult is to consider the patient holistically, looking at their cognitive, physical, audiometric (including speech understanding in noise), and overall abilities when recommending and selecting HAT. Current data suggest significantly lower than would be desired HAT penetration in this population. This is concerning in an aging population facing possible cognitive decline given that there appears to be an interaction between cognitive performance and appropriate HAT use. If patient performance and preferences are taken into consideration, it is possible that HAT uptake will increase as patients feel that their input and functional abilities are being considered. The automatic response to a diagnosis of hearing loss is often recommendation of hearing aids and/or cochlear implants when other devices may be more appropriate. Overall, access to auditory information is key to interacting with the acoustic/auditory environment. The means through which auditory access is achieved is patient-specific. Regardless of type of HAT, published data suggest that earlier use of HAT is associated with improved performance in the short and long term.