Conventional Amplification for Children and Adults with Severe-to-Profound Hearing Loss

Abstract

The primary goal of amplification is to restore audibility without causing discomfort; for someone with severe-to-profound hearing loss, the reduced dynamic range poses unique challenges in hearing-assistive device fitting. These challenges, including physiological limitation, processing difficulties, technology constraints, and other confounding factors, must be considered when selecting, fitting, and counseling for appropriate amplification. Many of the advanced features in hearing aids do not adequately address the unique characteristics of patients with severe-to-profound hearing loss. This review article will attempt to unravel some of the challenges and associated considerations when fitting adults and children with severe-to-profound hearing loss.

Learning Outcomes: As a result of this activity, the participant will be able to (1) describe the necessary steps in fitting a child or adult with hearing aids; (2) describe the benefits and downfalls of technology choices for people with severe-to-profound hearing loss.

The primary goal of amplification for listeners with hearing loss is to restore audibility for speech and minimize the likelihood of loudness discomfort. Both of these objectives can be achieved in most listeners with mild or moderate degrees of hearing loss. For listeners with severe or profound degrees of hearing loss, however, providing amplification through conventional hearing aids presents audiologists with unique challenges. Severe-to-profound hearing loss is defined as having an audiometric pure-tone average greater than 70 dB hearing level (HL), which means that without amplification, access to communication under normal conditions is extremely limited. The restoration of audibility in listeners with severe-to-profound hearing loss is hindered by a reduced dynamic range between the listener's thresholds and the level where sounds become uncomfortably loud. Even when audibility can be achieved, listeners with severe-to-profound hearing loss are more likely to have significant suprathreshold deficits than listeners with lesser degrees of hearing loss. For these reasons, the provision of conventional amplification for listeners with severe to profound requires special considerations. In this article, we describe the factors that influence hearing aid benefit in children and adults with severe or profound degrees of hearing loss and how those factors influence the hearing aid fitting process. Additionally, clinical outcome measures that can be used to assess hearing aid benefit for listeners with the greatest degrees of hearing loss are presented.

Early Research on Listeners with Severe-to-Profound Hearing Loss

Despite severe-to-profound hearing loss being identified many centuries ago, it was not until the 1950s that there was an electronic technology which allowed for the widespread production of hearing aids as an intervention for individuals with hearing loss. ¹ Despite being provided amplification, the published research at the time on the auditory and communication capabilities of listeners with severe-to-profound hearing loss suggested that they had poor communication outcomes and minimal speech understanding ability. ^{2 3} Even with hearing aids, many listeners with severe-to-profound hearing loss were able to detect only the presence or absence of sound in their environment. The ability to discriminate between or identify specific speech sounds was often achieved only with substantial aural (re)habilitation and auditory training or with visual support. The limitations experienced by those with severe-to-profound hearing loss were due to a combination of three primary factors. First, there are fundamental physiological limitations in the function of the auditory system once hearing loss reaches a severe degree. Second, amplification technology was unsophisticated by modern standards and limited the potential improvements in audibility that could be achieved. Third, intervention was often provided after substantial periods of auditory deprivation and was not provided consistently. Modern hearing aids and earlier detection and diagnosis of hearing loss have overcome some of the technological limitations and minimize periods of auditory deprivation during critical periods for language development, but significant upgrades in technology have not provided solutions to all difficulties experienced by persons with severe-to-profound hearing losses.

While the limitations of the auditory system remain a consistent barrier for providing listeners with severe-to-profound hearing loss with access to acoustic hearing through hearing aids, substantial progress has occurred since that time in hearing aid signal processing and fitting strategies that promote more consistent access to a wide range of sounds. Additionally, intervention is provided more rapidly than ever before in the form of working with families of infants and young children with severe-to-profound hearing loss shortly after diagnosis of hearing loss or after the acquisition of severe-to-profound hearing loss in adults. The physiological limitations of the auditory system in listeners with severe-to-profound hearing loss related to fitting hearing aids will be briefly highlighted, followed by a discussion of how these factors influence the fitting, verification, and validation of amplification for children and adults with severe or profound degrees of hearing loss.

The Effects of Severe-to-Profound Hearing Loss on the Auditory System

Sensorineural hearing loss is most often the result of malformation or damage to the structures of the cochlea or auditory nerve that cannot be corrected by medical or surgical intervention. The normal cochlea is able to respond to a wide range of sound intensities because of an active amplification process that occurs as the result of outer hair cells that respond mechanically to sound. ⁴ Inner hair cells in the cochlea serve as sensory transducers for those amplified signals on the basilar membrane. It is not a coincidence that the nonlinear amplification provided by the cochlear functions for signals with intensities up to approximately 70 dB HL. ⁵ Mild and moderate degrees of hearing loss are often characterized by a partial loss of the amplification function of outer hair cells. Because the sensory transduction of the cochlear inner hair cells is often preserved for mild or moderate degrees of hearing loss, restoring access to soft sounds with hearing aids is often an effective solution for compensating for outer hair cell loss. In a case of a cochlea without outer hair cells but with fully intact inner hair cells, the degree of the resulting hearing loss should theoretically be around 70 dB HL because that is the level of sound that is sufficient to be transduced by the inner hair cells without additional cochlear amplification. Hearing losses of 70 dB or greater are characterized not only by a loss of amplification from outer hair cells but a loss of sensory transduction from inner hair cells, synapses, or auditory nerve fibers. Hearing aids compensate for the loss of cochlear amplification but are inadequate to compensate for the distortion of the auditory signal that occurs when damage to other structures of the auditory nervous system occur. ⁶

Loss of low-level audibility is not the only consequence of damage to the cochlea or auditory nerve. The loss of the cochlear amplifier also contributes to abnormally rapid growth of loudness perception, known as recruitment. ⁷ Effectively, the level where sound becomes uncomfortably loud for a listener does not change, but thresholds have increased. The difference between auditory thresholds and loudness discomfort levels across the frequency range of hearing is known as the dynamic range or residual auditory area. ⁸ In order for amplified sound to be both audible and comfortable, hearing aids must be able to amplify and compress the 30-dB range of the average speech signal to fit into a listener's reduced dynamic range. For listeners with severe-to-profound hearing loss, the dynamic range may be only 20 to 30 dB between thresholds and the loudness discomfort levels.

Additionally, severe-to-profound hearing loss may be accompanied by damage to cochlear hair cells or the auditory nerve and those regions may no longer transduce sound at all. The so-called dead regions in the cochlea ⁹ create significant challenges for providing amplification for individuals with severe-to-profound hearing loss. Dead regions have been identified in children with severe-to-profound hearing loss. ¹⁰ Because those regions are minimally responsive to acoustic stimuli, attempts to provide amplification are unlikely to contribute to perception. A risk of amplifying dead regions is that the amplified signal can potentially mask other signals at other frequency regions because of the mechanics of the cochlear traveling wave and tonotopic organization of the cochlea. ¹¹ However, data from studies with adults have shown that providing amplification to dead regions has limited potential for negative consequences, outside of creating acoustic feedback by trying to amplify the high frequencies. ¹² Audiologists should be aware of the potential for dead regions in the cochlea for individuals with severe-to-profound hearing loss and recognize situations where attempting to increase audibility with hearing aids does not result in improved perception. Individuals with extensive dead regions may not experience high levels of speech recognition with hearing aids.

Temporal and Spectral Resolution

Speech has additional temporal and spectral cues that are necessary to decode for speech to be accurately understood. Recently, it has been suggested that those with cochlear hearing loss have a reduced ability to process temporal fine structure (TFS) information, which is even more problematic for those with severe-to-profound hearing losses. Temporal resolution refers to the ability to detect changes in acoustic stimuli over time. Classically, the measure used to determine temporal resolution is gap detection threshold. This is completed by measuring the smallest silent interval a person can detect. Additionally, other tests of temporal resolution include amplitude modulation distortion, duration discrimination, temporal order judgment, and temporal masking. Many studies have been conducted to evaluate the patterns of temporal resolution in persons with hearing loss. ^{13 14 15} Listeners with hearing loss perform more poorly than normal hearing listeners at tasks that are thought to depend heavily on TFS information such as interaural phase difference discrimination ¹⁶ and low rate frequency modulation. ¹⁷ These deficits have a negative impact on a listener's ability to decode temporal cues that are important for understanding speech. ¹⁸

There are several mechanisms that could account for those with cochlear hearing loss' inability to process TFS information. People with hearing loss have poorer frequency selectivity, ¹⁹ and the information sent to the central system could be distorted and, therefore, uninterpretable by the central auditory system. Furthermore, people with hearing loss have a reduction in the number of auditory nerve fibers; ²⁰ this is particularly true for those with severe or profound hearing loss. People with severe-to-profound cochlear hearing loss have an abnormal basilar membrane ²¹ and, therefore, will have difficulty coding an accurate TFS. TFS information is important in understanding speech in the presence of background noise. Despite being provided with appropriate amplification, persons with severe-to-profound hearing loss will not be able to overcome these physiologic factors which impact the coding of TFS. While hearing aids can improve the audibility of cues that may help support temporal processing, amplification cannot directly compensate for deficits in temporal processing for listeners with severe-to-profound sensorineural hearing losses.

Additionally, perception of spectral cues is impacted by severe-to-profound cochlear hearing loss, but not to the same extent as cues for perception of TFS. Spectral cues, such as formant frequencies and formant transitions, are related to the spectrum of the sound energy in a particular phoneme. Spectral information is an important cue for the identification of segmental phonemes and leads to effective frequency resolution of the auditory mechanism. The accurate perception and identification of these cues is essential to accurate speech perception. As described earlier, studies have shown that cochlear hearing loss is strongly associated with widened auditory filters, resulting in poor frequency resolution. Thus, listeners with cochlear damage will not be able to effectively use some of the spectral cues in speech. ²² Several authors have reported that listeners with hearing loss, particularly those with severe-to-profound hearing losses, have poorer than normal speech recognition when compared with listeners with normal hearing. ^{22 23 24} Some investigators suggest that poor frequency resolution and spectral smearing underlie this deficit. ²⁵

For accurate perception of sound, it is necessary for the distinct frequency cues of speech sounds to be accurately perceived; hearing aids may help with the amplification of these sounds. However, they are not able to overcome some of the physiologic changes in the auditory system when someone has a severe-to-profound hearing loss. As the spectral and temporal cues are essential for accurate discrimination of the speech cues, the lack of this ability will impact speech perception. While audible sound is important to accurate speech perception, listening is a cognitive task and requires processing by a central system for speech perception and translation.

Cognitive Factors

The ability to understand speech when the acoustic cues of speech are degraded relies heavily on the listener's cognitive abilities, such as working memory, and linguistic knowledge and experience. ²⁶ Listeners with severe-to-profound hearing loss who may only have partial restoration of audibility through hearing aids are likely to rely on their working memory and language skills to help understand speech. Adults who acquire severe-to-profound hearing loss after having developed spoken language and cognitive abilities are able to use these skills to support their communication in everyday listening environments. Children with congenital or prelingual severe-to-profound hearing loss will face additional challenges in the development of these critical skills without early intervention and amplification.

Recent evidence suggests that children with prelingual severe-to-profound hearing loss may experience deficits in working memory, ^{27 28} and executive function. ^{29 30} These deficits may result in a double penalty for children with severe-to-profound hearing loss, as the cognitive skills that support listening when the input signal is degraded may also be negatively affected by prelingual severe-to-profound hearing loss. These deficits have been linked to speech recognition deficits even after children with severe-to-profound hearing loss receive cochlear implants. ³¹

It should be noted, however, that recent evidence has challenged the notion that there is a causal relationship between prelingual severe-to-profound hearing loss and deficits in working memory and executive function. Hall and colleagues ³² measured a sequential learning task designed to reflect executive function in children with normal hearing, children with severe-to-profound hearing loss who use cochlear implants, and children with severe-to-profound hearing loss who use sign language. Unlike some previous studies, Hall and colleagues ³² demonstrated that there were no differences between the groups on the sequential learning task, even though the children who were deaf and used sign language had limited auditory experience. These results and others ³³ suggest that the deficits in working memory and executive function in children with severe hearing loss may be related to language abilities rather than limited auditory experience. Audiologists who support children with severe-to-profound hearing loss should be aware of the potential for deficits in language and cognitive abilities that may compound listening and learning problems.

The Relationship Between Audibility and Speech Recognition

The restoration of audibility from hearing aids often results in improved speech recognition for children ^{34 35 36 37} and adults ^{38 39} who wear hearing aids. The Speech Intelligibility Index (SII; ANSI S3.5–1997) is a standardized method of quantifying the audibility for speech that is often used to predict the degree to which speech recognition will improve as audibility improves. Transfer functions that relate audibility from the SII and speech recognition for adults have been developed for a range of different speech stimuli from nonsense words ⁴⁰ to continuous discourse. ⁴¹ The audibility for speech from the SII is often used as an outcome measure for children ⁴² and adults ⁴³ who wear hearing aids.

However, the improvements in speech recognition that occur with increased speech audibility from hearing aids are not uniform across all degrees of hearing loss. Pavlovic ⁴⁴ compared adult listeners with normal hearing to adults with varying degrees of sensorineural hearing loss to determine whether increases in audibility would result in consistent improvements in speech recognition as predicted by the SII and related transfer functions. The listeners with normal hearing and mild or moderate degrees of hearing loss improved in their speech recognition as audibility for speech increased. However, listeners with severe or profound hearing loss had speech recognition that increased at a much slower rate than was predicted by the SII transfer functions. This finding led Pavlovic et al to propose modifications to the SII calculation, including a broadband desensitization factor that reduced predictions of speech recognition as the degree of hearing loss increased. ⁴⁵ Subsequent research has attempted to develop frequency-specific desensitization factors ⁴⁶ to account for differences in the relationship between audibility and speech recognition across different frequency regions for speech.

Limitations of Acoustic Amplification for Listeners with Severe-to-Profound Hearing Loss

Excessive Amplitude Compression

The small residual dynamic range for listeners with severe-to-profound hearing loss can mean that speech amplified through a hearing aid must be significantly compressed to achieve audibility without making sound uncomfortably loud. If the amplitude of the speech spectrum becomes too compressed, speech cues related to changes in amplitude over time may be diminished and limit the effectiveness of amplification. Bor et al ⁴⁷ compared the effects of a range of compression channels in hearing aids for vowel identification in adults with severe hearing loss. The results indicated that as the number of channels of amplitude compression increased, more flattening of six of the eight vowels occurred. This poor spectral resolution as a result of excessive amplitude compression resulted in a decrease in the users' ability to identify vowels correctly. Individuals with hearing loss need a wide range of spectral variety in comparison to individuals with normal hearing. ⁴⁸ Audibility did not have a significant impact on the listeners' abilities to correctly identify vowels. ⁴⁷ The impact on vowel identification performance was likely due to the decreased spectral resolution involving formant frequencies, the entire spectral shape, and individual audiometric features. These results demonstrate that restoration of audibility through hearing aids for listeners with severe-to-profound hearing loss may limit the ability of the listener to use those cues to support speech recognition. Audiologists may need to adjust the amount of amplitude compression for listeners with severe-to-profound hearing loss to balance audibility, distortion, and comfort.

Adequacy of Hearing Aid Gain/Bandwidth by Degree of Loss

The degree of an individual's hearing loss may affect how adequately the amplification utilized is able to provide gain and an appropriate bandwidth. Kimlinger et al ⁴⁹ examined the effects of individuals' audiometric thresholds, stimulus type, and their devices on the audibility of high-frequency stimuli. A wider bandwidth will likely benefit listeners if they are able to obtain high-frequency cues that are audible. The degree of high-frequency cues that are audible depends on the degree of the user's hearing loss. In addition, the hearing aid's output across a range of frequencies and the type of stimulus utilized to measure the output also will affect the amount of audibility that can be obtained. The configuration of the listener's audiogram will affect the audibility of high frequencies. Those with a sloping configuration will likely be more affected than those with a flat configuration. As clinicians, it is important that we take these factors into consideration when determining the adequacy of user's hearing aid gain and bandwidth.

Potential for Overamplification

A potential exists for children with severe-to-profound hearing loss to receive excessive amplification from their hearing aids. According to Byrne et al, ⁵⁰ individuals with severe-to-profound hearing loss may require more amplification than would be typically recommended using the National Acoustic Laboratory (NAL) procedure, particularly in the lower frequencies when compared with those with a lesser degree of hearing loss and the same configuration on their audiograms. Individuals who have thresholds exceeding 95 dB HL at 2,000 Hz are typically those who benefit from a frequency response with more amplification in the lower frequencies. Overamplification can cause a variety of concerns for children with hearing loss.

The use of nonlinear hearing aids to treat children with hearing loss has a risk of damaging the children's hearing. ⁵¹ More specifically, the National Acoustics Laboratories Non-Linear 2 (NAL-NL2) procedure can become harmful when an individual's hearing loss exceeds 90 dB HL and Desired Sensation Level (DSL) m[i/o] can be harmful when the hearing loss exceeds 80 dB HL for moderate-level inputs and 70 dB HL for high-level inputs. Those who receive too much amplification may experience temporary threshold shifts or permanent threshold shift. ⁵² Asymptotic temporary threshold shifts that are at safe limits and not typically connected with permanent threshold shifts can be seen in individuals with pure-tone averages greater than 60 dB HL and less than 100 dB HL. ⁵³ Macrae ⁵³ developed a model to determine the amounts of asymptotic threshold shift to be expected using real-ear insertion gains (REIGs) when also utilizing the recommended NAL procedure. The amount of asymptotic temporary threshold shift would be considered unsafe when REIGs exceed 15 dB greater than what is recommended for individuals with pure-tone averages greater than 80 dB HL. In addition, the amount of amplification needed for those who have a pure-tone average greater than 100 dB HL may result in a permanent threshold shift. There is a potential for overamplification, which is partially due to the degree of the individual's hearing loss.

Research by McCreery et al ⁵⁴ evaluated the changes in thresholds of children who were fit with hearing aids utilizing the DSL prescriptive targets with two varying safety limits. The first safety limit focused on the child's dB HL threshold and predicted hearing aid output for a high input level. The second utilized the child's dB SPL threshold and measured hearing aid output. Children who were fit with amplification above the safety limit did not experience changes in their thresholds that were increased to those children who were fit with amplification under the safety limit. As a result, it was determined that utilizing hearing aid verification along with prescriptive targets will provide children with a mild to severe hearing loss with an acceptable safeguard from receiving increased hearing loss due to over amplification.

Changes Related to Ear-Canal Growth in Children

When infants are born, their external auditory canal (EAC) consists of only a cartilaginous portion. ⁵⁵ The osseous portion of the EAC develops over the first 3 years of the child's life. The EAC of infants and toddlers is much more flexible than that of older children and adults because of the fact that their EACs are still composed of mostly cartilage. In addition, the EAC of infants and children is shorter and straighter than the EACs of adults. ⁵⁶ The EAC is not considered to be adult in size until 9 years of age. ⁵⁵ These changes related to the EAC growth in children can ultimately affect how their amplification is fit to prescriptive targets using real-ear measurements. The acoustics of children's EAC can vary, even among children of the same age range. ⁵⁵ As the child's EAC develops and changes, the acoustics of the child's EAC also will change. ⁵⁷ More specifically, smaller EAC volumes consist of larger resonant peaks in the response of the EAC. These peaks will likely occur at higher frequencies. When verifying the hearing aids of infants and children, real-ear aided response (REAR) is typically used instead of REIG. REIG calculations typically utilize an adult real-ear unaided response, which is why REAR is often the chosen method. The smaller volume of the EAC of children will produce increased SPL at the eardrum when the EAC is occluded with a hearing aid that is producing sound as compared with an adult-size EAC. It is critical to take the changes related to ear-canal growth in children into account when fitting them with amplification. The volume of a child's EAC will ultimately affect the output response of the hearing aid. Taking these differences and changes into consideration will help determine the appropriateness of the fitting of amplification.

Potential for Poorer Accuracy of Abr Thresholds for Infants with Severe-to-Profound Hearing Loss

Determining accurate thresholds for infants and children with hearing loss is a critical aspect of their audiologic care. Electrophysiologic testing, such as an auditory brainstem response (ABR), is considered an essential piece of diagnostic testing for infants and children who are not yet able to complete behavioral testing. ⁵⁸ Research by McCreery et al ⁵⁹ reconfirmed that ABR thresholds are a strong predictor of a child's behavioral thresholds; however, the amount of accuracy between the ABR thresholds and behavioral thresholds depends on the degree of hearing loss. For infants who have a severe-to-profound hearing loss, a potential exists for the accuracy of their ABR thresholds to be poorer.

According to McCreery et al, ⁵⁹ ABR thresholds often underestimate the hearing loss for individuals who have a moderate or greater degree of hearing loss. To account for differences between ABR threshold and behavioral threshold for individuals with greater degrees of hearing loss, a frequency-specific correction factor was developed. The correction factors that were created resulted in increased accuracy when predicting behavioral thresholds for a variety of hearing losses. As a result, these correction factors improve the accuracy of ABR threshold estimates of behavioral thresholds for infants and children with severe-to-profound hearing loss. With more accurate thresholds, children may see more improved outcomes related to the appropriateness of their hearing devices to more consistent audibility. This is critical in order for these children to benefit from amplification and to achieve more typical developmental outcomes.

Options for Acoustic Auditory Access for Patients with Severe-to-Profound Hearing Loss

For those with severe-to-profound hearing loss, amplification through hearing aids is the primary option for acoustic audibility. Hearing aids should be provided as quickly as possible once hearing loss is identified for both children and adults. In the case of adults with long-standing hearing loss, their success with amplification will not only depend on their degree of hearing loss but also on the length of time the hearing loss has persisted without amplification. ⁶⁰ The selected hearing aid needs to be able to provide ample amplification and power to meet the needs of persons with severe-to-profound hearing loss. When selecting the device, physical limitations should be considered (e.g., Does the patient have a pinna? Does the patient have dexterity problems:); and then the aid should be selected based on the audiogram and patient preferences. In the case of severe-to-profound hearing losses, listening needs and the audiogram would typically necessitate a behind-the-ear style hearing aid. One also could argue that this device should be able to be connected to assistive devices and have a telecoil option for connectivity; these features are highly desirable, as in some cases they are the only means for providing auditory access.

The use of validated prescriptive targets is best practice for hearing aid fitting. ^{61 62 63 64} Two prescriptive methods have been developed and updated regularly to account for the changes in signal processing: NAL-NL2 and DSL v5.0. Despite the differences between these methods, both are reliable methods that consistently provide good outcomes for hearing aid users. Both methods also suggest the measurement of soft, moderate, and loud speech to verify appropriate audibility and signal compression.

Verification of hearing aid output is critical for many reasons, but most importantly for persons with severe-to-profound hearing loss, to ensure that the sounds are audible and not painful to the patients. ^{65 66 67} To ensure an appropriate fitting with any degree of accuracy, it follows that the hearing aid output must be measured in the ear canal or test box. There is a robust body of research supporting the use of both verification and validation of hearing aid fittings. ^{68 69 70} Patients see real-life benefits of verification; the use of verification and validation of hearing aid fit reduces the number of visits and increases patient success with amplification. ⁷⁰ Additionally, it has been demonstrated that patients prefer verified prescriptive fittings when compared with initial-fit approaches. ⁷¹ Furthermore, best practice guidelines recommend the use of validated prescriptive targets verified by real-ear measurement. ^{61 62 63 64}

Hearing-assistive technology consists of a variety of products, each with their own purpose and benefit. Those with severe-to-profound hearing loss have great difficulty hearing to communicate during activities of daily living. They may have difficulty hearing environmental sounds. Hearing-assistive technologies work to keep individuals with hearing loss aware and alert of various signals. Hearing-assistive technology may be an integral part of individuals with hearing loss receiving positive results. ⁷² The type of technology that is chosen is focused on the individual's communication needs. The technology may be used to alert the individual, help them listen, or be used as a signaling device. Individuals with hearing loss report that they are able to communicate better when they are using a remote microphone system along with their hearing aid compared with when they are using their hearing aid alone. In addition, those who utilize hearing-assistive technologies often report an increase in the ability to understand speech in complex listening environments. ⁷³ Communication can be a critical aspect of life. Those who utilize hearing-assistive technologies find these devices to be helpful and effective. As a result, the quality of their communication may improve through the use of these technologies.

One specific type of hearing-assistive technology that is beneficial are systems that use a remote microphone with the signal then transmitted wirelessly to the hearing aids (transmission may be Bluetooth, FM, etc.). The transmitting microphone is placed a few inches away from the source, which could be the speaker's mouth. ⁷³ The listener has a receiver in the hearing aid (or in a body-worn device that communicates with the hearing aid) that receives the transmitted signal from the microphone. As a result, remote microphone systems provide individuals with an improved signal-to-noise ratio. Hearing-assistive technologies can be extremely beneficial for children with severe-to-profound hearing loss in the classroom. Use of these technologies in the classroom can result in improvements of speech understanding, psychoeducational, psychosocial, and academic improvements. ⁷⁴ These improvements can greatly impact the use of conventional amplification for those with severe-to-profound hearing loss.

Outcomes Validation for Patients with Severe-to-Profound Hearing Loss

Documenting outcomes for children and adults who wear hearing aids is an essential component of the amplification process. ^{37 42} For people with severe-to-profound hearing loss, monitoring outcomes can be helpful for determining the limits of performance with amplification and potential need for cochlear implantation. Given that many children and adults with severe-to-profound hearing loss will receive cochlear implants as their primary intervention, many individuals will be required to have a trial with hearing aids where outcomes will be documented prior to pursuing cochlear implants. Others may start with mild or moderate degrees of hearing loss and progress into the range of cochlear implantation. In any case, appropriate documentation of hearing aid outcomes will help support clinical decisions about cochlear implant candidacy or further optimization of hearing aids.

The ability to understand speech with hearing aids is an important outcome measure for any hearing aid user. Protocols and minimum test batteries have been reported for adults ⁷⁵ and children. ⁷⁶ The goal of aided speech recognition assessment is to determine how a listener can understand speech with their hearing aids. Generally, aided speech recognition for children and adults should be completed at levels equivalent to average speech (60 or 65 dB SPL) using materials that are appropriate for the listener's age and auditory skills. Speech recognition in noise should be measured for listeners who can achieve high levels of speech understanding in quiet (>84% correct). The interpretation of aided speech recognition testing is based on several factors, including the amount of aided audibility that has been restored with hearing aids, the listener's age, comorbid developmental conditions, and the type of stimulus used for the test. Several patterns of speech recognition results may indicate the need for further assessment or referral for cochlear implant candidacy evaluation. Listeners with appropriate audibility for their degree of hearing loss who have disproportionately poor speech recognition ⁷⁷ may have problems related to spectral or temporal resolution that are not reflected in the audiogram. In children, speech recognition skills are expected to progress as language and cognitive skills improve over time. A failure to improve in speech recognition abilities during preschool or elementary school years may be an indication that hearing aids are not providing sufficient access to support listening and learning. Overall, the utility of aided speech recognition is high and can be completed over a wide range of ages.

Self- or parent-report questionnaires are another option for assessing the impact of hearing aids on a listener's or caregiver's perception on their everyday listening situations. A large number of questionnaires have been recommended for both children ⁴² and adults. ⁷² Questionnaires for children are typically completed by the parents or caregivers and are focused on listening and language skills, as well as how the children function in a range of listening environments. Children should show progress over time on parent-report questionnaires ³⁷ and failure to improve over time may be an indication of limited benefit from amplification. However, because questionnaires for children are focused on broad areas that can reflect delays in language, cognition, and behavior, low scores on these measures cannot necessarily be attributed to auditory factors. Multidisciplinary developmental assessment including developmental pediatrics, speech–language pathology, occupational therapy, and other professions may be needed to fully characterize the contributions to limited progress on developmental questionnaires for children with severe-to-profound hearing loss.

Questionnaires for adults tend to focus on quality of life or specific problem areas that are important to the individual (listening in background noise, the ability to understand a significant other, etc.). Scores on questionnaires for adults can be useful in determining how well hearing aids are meeting the listener's expectations and the impact that their hearing loss might be having on their quality of life or relationships. Responses on these measures that indicate that an individual is experiencing a reduction in social activities, declining interpersonal relationships, hearing-related stress, or avoidance of social situations with hearing aids can be indicators of limited amplification benefit. In some situations, problems in these areas can be addressed by providing communication strategies, hearing-assistance technology, or tools to enhance connectivity. Solutions that focus specifically on the listener's stated needs and goals can help improve access and functioning in real-world listening environments.

Conclusions

There are a variety of options available for conventional amplification for children and adults with severe-to-profound hearing loss; additionally, there are many influencing factors when considering the appropriate technology choice. For some patients, the hearing aid is the only option that gives them access to auditory information. For other patients, it is the first step on their journey toward a cochlear implant. There are significant considerations that need to be made with regard to the technology choices including the features, accessibility and compatibility of hearing aids, and hearing-assistive devices. Personal factors such as cognition, age, and support systems should be considered when selecting devices and counseling. Appropriate and consistent counseling should be part of the audiologic rehabilitation process. Finally, outcome measures should be obtained at regular intervals to assess if the rehabilitation/hearing-assistive technology choices are appropriate and are providing the individual with severe-to-profound hearing loss the ability to achieve communication competence.