Background and Rationale for a Transitional Intervention for Debilitating Hyperacusis

Abstract

Purpose:

This report provides the experimental, clinical, theoretical, and historical background that motivated a patented transitional intervention and its implementation and evaluation in a field trial for mitigation of debilitating loudness-based hyperacusis (LH).

Background and Rationale:

Barriers for ameliorating LH, which is differentiated here from other forms of hyperacusis, are delineated, including counterproductive management and treatment strategies that may exacerbate the condition. Evidence for hyper-gain central auditory processes as the bases for LH and the associated LH-induced distress and stress responses are presented. This presentation is followed by an overview of prior efforts to use counseling and therapeutic sound as interventional tools for recalibrating the hyper-gain LH response. We also consider previous efforts to use output-limiting sound-protection devices in the management of LH. This historical background lays the foundation for our transitional intervention protocol and its implementation and evaluation in a field trial.

Conclusions:

The successful implementation and evaluation of a transitional intervention, which we document in the outcomes of a companion proof-of-concept field trial in this issue, build on our prior efforts and those of others to understand, manage, and treat hyperacusis. These efforts to overcome significant barriers and vexing long-standing challenges in the management and treatment of LH, as reviewed here, are the pillars of the transitional intervention and its primary components, namely, counseling combined with protective sound management and therapeutic sound, which we detail in separate reports in this issue.

In this report, we review the theoretical, clinical, and empirical background and historical literature motivating the development and evaluation of a patented transitional intervention (Eddins et al., 2020) for primary loudness-based hyperacusis (LH; Tyler et al., 2014). The rationale for our patented intervention, which incorporates a structured counseling protocol together with protective output-limiting sound management and therapeutic low-level broadband sound from fully digital bilateral ear-worn devices, follows from evidence that ongoing sound avoidance and isolation are counterproductive (Formby et al., 2003; Formby, Sherlock, et al., 2007). In contrast, sound-enriching treatments and behaviors of the kind described below promote amelioration of the LH condition with marked increases in quality of life. We overview prior efforts to use counseling for treatment of hyperacusis, including LH and associated variants variously categorized as annoyance hyperacusis (AH; misophonia), fear hyperacusis (FH; phonophobia), and pain hyperacusis (PH; see P. J. Jastreboff & Jastreboff, 2000, 2014, 2015, 2016; Tyler et al., 2014). The success of these various counseling approaches and models shaped the counseling protocol (Cherri et al., 2024), which we developed for use in our transitional intervention. We also review past efforts to engineer output-limiting sound management strategies with high-compression electronic ear-worn devices as a protective tool for LH patients. These early attempts to use active output-limiting devices to restrict exposures to potentially offending sound levels guided our efforts to devise a progressive protective sound management protocol for LH. The resulting device and fitting protocol, developed for use by LH patients in safe, controlled sound environments (without output-limiting sound protection) and in high-risk, uncontrolled sound environments (with output-limiting protection), is described in a separate companion report in this issue (Eddins et al., 2024). The latter report also details our primary therapeutic tool for promoting improved sound tolerance and resolution of LH using neutral, low-level, broadband sound delivered bilaterally by ear-worn sound generators. Here, we review the empirical and clinical evidence that supports this use of sound therapy for treating LH. In this context, we also review related scientific evidence and theoretical conjecture that links LH to maladaptive hyper-gain central auditory processes and the use of therapeutic sound for recalibrating these gain processes. At the conclusion of this report, we overview our interventional protocol, which is designed to restore homeostatic gain within the central auditory pathways leading to resolution of LH and improved quality of life in typical everyday sound environments. Subsequently in this issue, we describe the successful implementation and evaluation of our transitional intervention in a 6-month field trial and the promising outcomes of the trial (Formby et al., 2024).

Background and Rationale

The Many Faces of Hyperacusis

In its classical presentation, LH (Tyler et al., 2014) is an atypical condition that is characterized by an unusual intolerance to everyday sounds (Vernon, 1987). LH reflects inordinately enhanced activation of the auditory pathways (P. J. Jastreboff & Hazell, 2004) and abnormally increased suprathreshold sensitivity to sound levels that are not bothersome to most individuals.

Sound is omnipresent in our natural environments, existing over a wide range of levels. Indeed, the normal auditory system is remarkable in that it has a very large dynamic range defined by the continuum of levels between audiometric threshold and the loudness discomfort level (LDL). In some individuals, this range can be as great as 120 dB or a staggering 1,000,000,000,000-fold change in sound intensity levels from low to high. We rely on this large dynamic range in our everyday lives as we encounter, create, enjoy, and make use of the sounds in our environments. Patients with LH have a markedly reduced dynamic range, resulting from lower-than-normal LDLs and, in some cases, higher than normal audiometric thresholds. LH is related to acoustic features that impact the loudness of a sound (i.e., level, duration, and spectral content) rather than the context, meaning, source, or other aspects of the pitch or quality of the sound.

For most individuals with hyperacusis symptoms and complaints, there is no known cause, despite large numbers of auditory and nonauditory conditions and disorders variously linked with hyperacusis (McFerran, 2018). While hyperacusis may or may not be observed together with measurable audiometric hearing loss, hyperacusis has often been associated with acoustic trauma or ototoxicity (see the following reviews: Auerbach et al., 2014; Eggermont, 2018; Pienkowski et al., 2014; Roberts et al., 2018; Salvi et al., 2021; Schaette, 2018). This apparent causal association has led to consensus that decreased sensory output from damaged cochlear and peripheral auditory processes evokes compensatory increases in neural activity within the central auditory pathways; the resulting hyper-gain response ostensibly gives rise to hyperacusis (see above reviews). Consistent with the involvement of higher auditory processes, hyperacusis is almost always a bilateral condition and most often a symmetric problem affecting the loudness of sounds relatively uniformly across frequency (Aazh & Moore, 2017; Baguley & Hoare, 2018; Formby, Gold, et al., 2007; Sheldrake et al., 2015). As the severity of the hyperacusis condition increases, accompanying problems often manifest, including negative emotional and physiological reactions that amplify and compound the hyperacusis condition. These negative reactions may affect the thoughts, hearing, sleep, and concentration of the individual with hyperacusis (Tyler et al., 2015).

As noted above, a growing body of research links LH with central neuronal hyperexcitability both within and outside of specific auditory areas of the brain (Chen et al., 2015; Gu et al., 2010; Salvi et al., 2021). This elevated central neural activity is commonly associated with reduced sound input from the auditory periphery. Use of hearing protection devices (HPDs) represents a form of partial sound deprivation with some consequences common to peripheral hearing loss. Reduced input to the auditory system, in the cases of documented audiometric pure-tone hearing loss and other forms of auditory processing disorders, including hidden hearing loss (Hickox & Liberman, 2014; Liberman et al., 2016), can induce compensatory changes that give rise to increased neuronal activity within the central auditory pathways (see Auerbach et al., 2014; Eggermont, 2018; Henry, 2022; Roberts et al., 2018; Salvi et al., 2017). It is this heightened neural response (i.e., maladaptive hyperneural gain) that we and others now believe underlies the abnormally increased suprathreshold sensitivity of the LH patient (Auerbach et al., 2014; Brotherton et al., 2015; Eggermont, 2018; Formby & Gold, 2002; Hazell & Sheldrake, 1992; Henry, 2022; P. J. Jastreboff & Hazell, 1993; Roberts et al., 2018).

There is no consistent estimate of the prevalence of hyperacusis in the general population. This difficulty estimating prevalence stems largely from challenges in specifying and defining the nature of the hyperacusis problem (see below). A recent review of the literature reported a prevalence range of 0.2%–17.2% (Ren et al., 2021), with most prevalence estimates less than 10% (Baguley, 2018). Approximately 2% of affected individuals are estimated to suffer a clinically significant problem (Baguley, 2018; P. J. Jastreboff & Jastreboff, 2015). Furthermore, a wide range of conditions that include symptoms of hyperacusis also have tinnitus as common comorbid condition (Tyler et al., 2014).

It is important to distinguish classical LH from other forms of abnormal suprathreshold sound sensitivity. These anomalous conditions are variously considered generically as hyperacusis. Over the past 20 years, specific symptomology and characteristics of abnormality have been recognized for the different forms of hyperacusis delineated in the categories below. There is no definitive audiometric cutoff below which LH can be ascribed; however, for debilitating conditions of LH, LDL judgments for tonal signals are typically less than ~75 dB HL (see below), with associated reported distress. Individuals who experience LH characteristically report that sounds of moderate level, and sometimes less intense sound levels, are perceived as uncomfortably loud. LH contrasts with the condition of supersensitivity for which the audibility of sounds is atypically keen and reflects better than normal audiometric detection thresholds (Tyler, 1999). Likewise, LH, characterized by abnormally low LDLs, differs from sound tolerance conditions for which a reduced dynamic range arises from an individual's elevated audiometric thresholds with typical LDLs (i.e., loudness recruitment). The latter characterization of a reduced auditory dynamic range is perhaps most relevant in classifying loudness-based disorders for which the dynamic range of an individual with hearing impairment is much less than 60 dB (Goldstein & Shulman, 1996). This is not a target group for implementation of our current treatment device and transitional protocol. However, our treatment device and protocol can be adapted for persons with hearing impairment, including those with borderline normal sound tolerance and those with loudness recruitment and limited dynamic ranges for loudness. These are individuals who may be unable to tolerate amplified sound but can be treated successfully with counseling and sound therapy as described by Formby et al. (2015, 2017).

Other atypical sound-induced conditions are characterized by responses to sounds that may be largely unrelated to the physical properties of the offending sounds (see Henry et al., 2022; M. M. Jastreboff & Jastreboff, 2001, P. J. Jastreboff & Jastreboff, 2016; Phillips & Carr, 1998; Tyler et al., 2014). These conditions include misophonia and phonophobia (i.e., dislike of or annoyance with and fear of exposure to specific sounds or classes of sounds, respectively), which have clusters of characteristics that are quite distinct from LH (and the LH-related distress and stress responses). These latter conditions may require interventional approaches that are different from, or in addition to, those described here for treating LH (see P. J. Jastreboff & Jastreboff, 2014). In part, because of confusion with the usage of the term “misophonia” and its subsequent promotion as a distinct psychiatric disorder in the psychology and psychiatry community (Brout et al., 2018; Dozier et al., 2017; Schröder et al., 2013), Tyler et al. (2014) proposed simpler descriptive terms for both misophonia and phonophobia. They recommended the use of “AH” and “FH,” respectively, to replace the terms misophonia and phonophobia. However, the distinction between LH (primary hyperacusis) and misophonia may become complicated in severe cases of hyperacusis. P. J. Jastreboff and Jastreboff (2014) posit that debilitating LH can induce misophonia and phonophobia, thus, exacerbating the angst to specific sounds or classes of sounds. Indeed, P. J. Jastreboff and Jastreboff (2014) have reported that 92% of a patient sample of 201 individuals with decreased sound tolerance (including some with primary hyperacusis) suffered some degree of misophonia. They note that this form of hyperacusis-induced misophonia is different from that which has been proposed as a distinct psychiatric condition (P. J. Jastreboff & Jastreboff, 2014) and, also, presumably different from the typical distress and stress responses that often accompany LH. Pain associated with offending sound is yet another form of atypical sound-induced response that may or may not be associated with LH. This poorly understood condition is commonly referred to as “PH” (Tyler et al., 2014).

The above four categories of sound-related hyperacusis conditions (LH, AH, FH, and PH) provide clinicians and researchers with a framework with which to disentangle the phenomenological characteristics and associated symptoms leading to appropriate diagnoses for planning management and treatment of hyperacusis. However, two or more of these categories may co-occur for some (if not most) individuals with hyperacusis complaints, requiring differential treatment strategies for the respective categorical components of the decreased sound tolerance condition. Most notably, P. J. Jastreboff and Jastreboff (2014, 2016) report that LH can be successfully treated with sound generators and other forms of neutral enriched low-level sound therapy per the desensitization strategy outlined originally by Hazell and Sheldrake (1992), whereas AH cannot be successfully treated with this approach. Instead, AH (and FH) may require sound-specific desensitization approaches to remediate the condition. Such desensitization strategies with low-level and high-level sound protocols have been proposed, respectively, by Tyler and his colleagues (Tyler et al., 2015) and by Vernon and his colleagues (Vernon, 1987, 2002; Vernon et al., 2002). In this report, our focus is on classical LH and its management and treatment with a transitional (low-level sound enrichment) intervention protocol. In debilitating cases of LH, the limbic and autonomic nervous systems may become involved, giving rise to untoward emotional distress and physiological stress responses. The current treatment may be effective in reducing these and possibly some of the maladaptive responses encountered in the other forms of hyperacusis.

Barriers to Successful Treatment of LH

The most successful intervention strategies to date for treating LH have used some form of therapeutic sound (Fackrell et al., 2017). There are two major challenges for any interventional approach that promotes the use of therapeutic sound for treating debilitating LH, namely: (a) transitioning the affected individual from counterproductive use of HPDs to acceptance and use of safe, controlled, enriched therapeutic sound (i.e., typically from ear-worn devices and healthy environmental sound sources within the home) that, through auditory gain modification, induces expansion of their dynamic range for loudness and, ultimately, alleviation of the hyperacusis condition; and (b) empowering the affected individual to leave behind their comfort zones associated with isolation and silence. This latter unhealthy lifestyle is often self-imposed through extreme isolation from family and friends, augmented by their overuse of HPDs (Vernon, 2002; Vernon et al., 2002). Vernon et al. (2002) aptly described these detrimental effects in terms of “a vicious circle,” which they relate as follows:

The typical hyperacusis patient initially wears ear plugs upon venturing outdoors. Then such patients discover that ear plugs alone are not sufficient protection and they begin to wear earmuffs over their ear plugs. And then in short order they find that this dual protection is insufficient causing them to become reclusive, not venturing out at all. They mistakenly attribute the increase in their hyperacusis to the presence of the uncomfortable sounds they have had to endure when, in fact, the increased hyperacusis has been due to their over protection and not the sound discomfort they had experienced.” p. 173, Vernon et al., 2002)

Consequently, the first challenge in our intervention (or any intervention) for LH is to disrupt this “vicious circle.” It is only then that we can initiate treatment to resolve the hyperacusis.

Consistent with Vernon et al.'s (2002) description above, it is common for a patient who develops LH to engage in forms of self-treatment focused on sound avoidance. The simplest self-avoidance behavior is to alter routine activities to avoid visits to locations or sound environments where one is likely to encounter loud, bothersome sounds. This maladaptive behavior often leads to major life-altering changes that limit comfortable enjoyment of many previously normal activities and, ultimately, to a diminished quality of life. These detrimental sound avoidance behaviors are typically viewed by the affected individual as necessary coping mechanisms, and often are supplemented using HPDs, including ear plugs, ear muffs, or both. HPD use and sound avoidance behaviors may be rational responses to LH; however, both require irrational efforts to implement. For example, it is impractical to be perpetually prepared to don HPDs just in time before an unexpected offending loud sound is present. As a result, HPDs are often overused and misused in anticipation of potentially offending sounds. While HPDs offer a protective benefit to the patient by limiting exposure to offending sound levels, the resulting attenuation affects the full dynamic range of sound levels. This adverse effect deprives the auditory system of healthy exposure to sound levels that are comfortable without attenuation and that are essential for maintaining the typically large auditory dynamic range for loudness, which normally spans about 95 dB (Sherlock & Formby, 2005). As described below, this sort of sound deprivation also has been shown to induce mild forms of suprathreshold hypersensitivity in persons with normal-hearing sensitivity and loudness tolerance (Formby et al., 2003; Formby, Sherlock, et al., 2007); the resulting adverse and counterproductive effects of HPDs may be that of exacerbating the hyperacusis condition. If the patient also has hearing loss, then the use of HPDs compounds that condition by further reducing audibility and the dynamic range for loudness. Thus, hyperacusis patients who present wearing ear plugs, ear muffs, or both, as a “treatment” for hyperacusis represent a major clinical challenge.

To overcome these major barriers to a successful intervention for LH, the clinician must help the patient to understand the importance of safe and healthy sound exposure throughout the day. The clinician also must encourage the patient to reduce and successfully end their reliance on HPDs so that they can benefit from healthy sound exposure as well as sound enrichment therapy (described below). Counseling is obviously important for addressing these issues and any associated inordinate negative emotional or physiological responses, or both (i.e., distress, stress) to LH.

Negative Effects of Sound Attenuation and Positive Effects of Sound Enrichment

The negative effects of sound-attenuating treatments and the positive effects of sound-enriching treatments for hyperacusis are perhaps best exemplified in our past research with sound-attenuating ear plugs and ear-worn sound-enriching generators used bilaterally by listeners with normal-hearing sensitivity and normal loudness perception. These respective treatment effects conceptually reflect the adaptive plasticity of underlying central auditory gain processes in the control of loudness judgments. In the first of our two studies designed to delineate these opposing effects in individuals with normal hearing sensitivity and normal loudness tolerance, Formby et al. (2003) assigned one group of eight individuals to use of bilateral ear plugs for 23 hr a day for a duration of 2 weeks. At the end of the sound-attenuating treatments, the participants' categorical loudness judgments for warble-tone levels judged to be “comfortable” and louder decreased in level by 5–8 dB. In contrast, a similar group of eight participants, exposed to continuous low-level broadband noise from bilateral sound generators (under comparable conditions of usage to those wearing the ear plugs), judged the loudness of warble-tone levels corresponding to categorical judgments of “soft, but comfortable” up through “uncomfortably loud” to increase in level by 4–8 dB. Thus, posttreatment, the partially sound-deprived participants using sound-attenuating ear plugs became more sensitive to the loudness of the warble tones, whereas the sound-enriched participants using sound generators were less sensitive to the loudness of the same tones (Formby et al., 2003). This differential plasticity of the auditory system to chronic use of the sound-attenuating and sound-enriching treatments reflects decreases and increases, respectively, in the peripheral sound input to the central auditory pathways. The resulting decreases and increases in sound exposure, in turn, affect predictable compensatory changes in central auditory pathway gain with the former inducing increased gain and the latter affecting decreased gain. Notably, these treatment effects were the same when measured at either 500 or 2000 Hz even though both treatments produced shifts in audibility thresholds mainly at 2000 Hz and had little to no effect on audibility at 500 Hz. This result strongly implicates centrally mediated treatment effects consistent with modification of central gain processes.

Formby, Sherlock, et al. (2007) replicated the results of Formby et al. (2003) in a subsequent study using a cross-over design in which eight participants were randomly assigned initially to either ear plugs or sound generators used bilaterally for 4 weeks and then, after a washout period, were switched into the alternative treatments. In both the 2003 and 2007 studies, the respective treatment effects tended to increase with the increasing sound level associated with the categorical loudness judgments (Formby et al., 2003; Formby, Sherlock, et al., 2007). Thus, these results are consistent with those of other investigators who have variously demonstrated central auditory plasticity in both the brainstem and auditory cortex in response to prolonged unilateral ear plug use (see Hutchison et al., 2023). Together, this and related lines of research indicate that the auditory system is plastic and the gain of the system can be manipulated adaptively by taking advantage of this plasticity in response to appropriate sound deprivation and enrichment.

Our clinical and related research studies (e.g., Formby & Gold, 2002; Formby, Gold, et al., 2007; Formby et al., 2015, 2017; Gold et al., 1999, 2002) and those of others (e.g., Dauman & Bouscau-Faure, 2005; Hazell & Sheldrake, 1992; Henry, 2022; Henry et al., 2022; P. J. Jastreboff & Jastreboff, 2000) also have demonstrated that sound (enrichment) therapy, implemented using low-level broadband noise from bilateral sound generators, is effective in treating LH and decreased sound tolerance. This evidence has been revealed in multiple ways: systematic expansion of the auditory dynamic range for loudness; incremental shifts in LDLs (or uncomfortable loudness levels) for tones, white noise, and speech signals; and subjective improvements in sound tolerance often leading to resolution of the hyperacusis condition of the individual with enhanced quality of life. These positive treatment effects have been reported among persons with varying conditions of hyperacusis, with and without hearing loss and tinnitus. These latter conditions may complicate and, in some cases, confound the treatment of LH. As described below, these positive sound therapy effects often are meaningfully enhanced in the treatment of LH when combined with counseling.

Treatment Approaches for Hyperacusis

Comprehensive reviews of treatment approaches for hyperacusis and decreased sound tolerance can be found in several recent publications and are beyond the scope of this report (see Fackrell et al., 2017; Fagelson & Baguley, 2018; Henry et al., 2022; Pienkowski et al., 2014). Incorporated into the treatment approaches reviewed above are counseling (Fackrell et al., 2017), cognitive behavioral therapy (CBT; Aazh et al., 2019; Jüris et al., 2014), sound therapy (Formby et al., 2015; Hazell & Sheldrake, 1992; Henry, 2022; Pienkowski, 2019; Tyler et al., 2015), social support (Fagelson & Baguley, 2018), medication, (Pienkowski et al., 2014), Hyperacusis Activities Treatment, (Perreau et al., 2019; Tyler et al., 2022), Tinnitus Retraining Therapy (TRT; P. J. Jastreboff & Hazell, 2004), use of HPDs (Formby et al., 2003), and combinations of those treatments. The most successful interventions reported to date for hyperacusis have used therapeutic sound in some form, usually combined with counseling, but not always (see Noreña & Chery-Croze, 2007). Notwithstanding a single-site survey in which 92 hyperacusis patients ranked counseling to be the most effective treatment for their condition (Aazh et al., 2016), counseling alone is rare (see Fackrell et al., 2017) and when reported most often follows principles of CBT (Aazh et al., 2019; Jüris et al., 2014). CBT has been used with some success for treating hyperacusis; however, CBT and related counseling treatments for hyperacusis routinely include and use desensitizing exercises with sound. This includes Hyperacusis Activities Treatment, which offers hyperacusis patients the options for at least three different desensitizing sound therapy approaches (Perreau et al., 2019). The resulting treatment-related effects for CBT, at least as measured by incremental LDL change, are typically not as large as those reported for protocols combining ear-worn sound therapy (i.e., use of low-level broadband sound generators) and counseling (see Formby et al., 2015, 2017; Formby, Gold, et al., 2007).

To our knowledge, the earliest research documenting audiometric evidence for use of ear-worn therapeutic-sound devices for treatment of LH is a seminal proceedings report from Hazell and Sheldrake (1992). They described clinically significant increases in LDLs bilaterally, on the order of 8–10 dB across most of the audiometric frequency range, among a group of hyperacusic tinnitus patients who used incrementally increasing low levels of neutral broadband sound from bilateral tinnitus “maskers.” The maskers were in use ~6 hr each day. After 6 months of this “desensitization” intervention, about 75% of their patient group (n = 30) achieved positive treatment effects. They ascribed their impressive results to modification of maladaptive auditory gain processes, ostensibly mediated through efferent neuronal mechanisms. Although Hazell and Sheldrake reported the use of counseling as part of the sound therapy intervention, the nature of this counseling was not specified in their report. Subsequently, their sound therapy protocol was married with principles espoused by P. J. Jastreboff (1990) in his neurophysiological model of tinnitus. Their combined counseling and sound therapy approach evolved into the intervention known popularly today as TRT (P. J. Jastreboff & Hazell, 2004). TRT now includes dedicated protocol components for treatment of LH, AH, and FH, each of which can be offered separately from the TRT protocol for primary tinnitus (P. J. Jastreboff & Jastreboff, 2014, 2016). TRT-related LDL change for individuals using bilateral sound generators for debilitating primary LH may exceed 20 dB over the course of treatment (see Formby, Gold, et al., 2007). Corresponding subjective improvements in sound tolerance typically track closely with the objective changes in the individual's LDL judgments over the course of treatment (Gold et al., 1999, 2000, 2002).

Protective Management for Hyperacusis

Several investigators have described interventions that formally embrace protective sound management for hyperacusis. For example, Vernon et al. (2002) stated that their protective strategy and sound-limiting instruments (the Star 2000 and 2001) arose as a tool to mitigate overprotection of the hyperacusis patient. This idea, also described independently by Preves et al. (1995) and by Nunley (1996), was to engineer a loudness-suppressing wearable device that would limit exposure to offending higher level sounds, while ensuring audibility for soft sounds and comfort and tolerance for moderate level sounds. In short, the protective output-limiting strategy in each case above was achieved by engineering a special hearing device. The best description of one of these device designs was reported by Sammeth et al. (2000). It followed from Preves et al. (1995) and required the use of a snugly fitting, unvented, full-concha, in-the-ear device that functioned as an HPD to produce large amounts of attenuation. The resulting attenuation served to reduce exposure to offending high-level sounds within the environment. The insertion loss from the occluded ear was offset with low-level unity-gain amplification. The unity gain (ideally) restored audibility of low-level sounds across frequency and promoted typical transmission of all sound levels below an upper-limit. Above this level, all sound levels were uniformly compressed (with a high compression ratio) such that the perceived loudness of these potentially offending sound levels was suppressed and remained tolerable for the hyperacusis patient. It appears that the output limiting compression affording this loudness suppression (LS) was adjustable (above ~65 dB SPL) in most or all these devices and was designed to achieve a lower threshold setting for activation of the compression than would typically be set for most hearing-aid users.

We are not aware that any of these early device reports implicitly or explicitly described or considered an adaptive treatment-related strategy for adjusting the output-limiting, perhaps because there was no consensus evidence for an effective treatment approach for hyperacusis at that time. Indeed, the recommendation for sound-attenuating ear plugs as an intervention for hyperacusis was still common at the turn of the century (Formby et al., 2003). However, Vernon and his colleagues (Vernon, 2002; Vernon et al., 2002) were promoting a “pink noise” desensitization treatment protocol in his reports in which the Star 2000 and 2001 devices were described. Although Vernon's desensitization approach, as he described it, would seem to offer an ideal strategy for directing adaptive treatment–driven adjustment of the output-limiting settings in the Star devices, he never linked device adjustment with his adaptive treatment approach for LH. Westcott (2006) would later suggest the idea of adaptive treatment-related adjustment of output-limiting for LH in a report adopting Vernon's protective strategy; however, she also apparently did not implement adaptive adjustment of output-limiting in her research. (We should note here that other investigators, including Searchfield and Selvaratnam [2018] and Tyler et al. [2022], have since proposed adjustment of output-limiting settings in hearing aids as a tool for managing the sound tolerance problems of hyperacusis patients with hearing loss.). Despite the promise of these early sound-protection devices and suggestions for their usage, none of these devices or strategies described above achieved clinical or commercial success for managing and treating hyperacusis, and none of these products are being manufactured today (see Eddins et al., 2024).

Wearable Sound Generators for Treatment of Hyperacusis

The use and evolution of wearable sound generators for treatment of hyperacusis follows from the seminal report by Hazell and Sheldrake (1992). Their broadband “noise maskers” were relatively crude analog devices designed for tinnitus masking protocols. Similar devices were being used in the early and mid-1990s for treatment of hyperacusis in the Tinnitus and Hyperacusis Center at the University of Maryland, Baltimore. These sound therapy devices included behind-the-ear units (models AMTi, ARPPTi, and Silent Star, from Viennatone, a subsidiary of GN ReSound) fitted with nonoccluding earmolds (Formby, Gold, et al., 2007), and later an all-in-the-ear nonoccluding digital unit (the Tranquil model, General Hearing Instruments [GHI]). The latter was commissioned to produce a stable wide-band noise source, with low-noise background, adjustable to a quiet noise floor (this latter product evolved out of efforts to engineer the digi-K-amp per Roger Juneau, personal communication, 2022). Notably, the nonoccluding feature of these units was designed to facilitate communication and ensure the audibility of sound sources within the environment. Subsequently, Henry et al. (2002) related that only three models were deemed acceptable for use in TRT, including the Viennatone Silent Star, the GHI Tranquil, and a Spanish-built Audiphon device. These and similar ear-worn sound generation devices, now offered in some configuration by most major manufacturers of hearing devices, have since been used in various treatments (primarily based on TRT or related protocols) to achieve incremental shifts in the LDLs of patients with primary tinnitus, hyperacusis, or some combination of the two conditions. These treatment effects for primary hyperacusis, reflecting incremental change in the LDLs on the order of 20 dB, are appreciably larger than those originally reported by Hazell and Sheldrake (1992; or by others subsequently) for tinnitus patients with hyperacusis or similar treatment effects reported for primary tinnitus (see Formby, Gold, et al., 2007). In general, among those individuals with hyperacusis who have been responsive to their treatments, lower pretreatment LDLs tend to be predictive of larger treatment-related LDL change (Formby, Gold, et al., 2007). Finally, at least one early study reported a treatment effect slightly smaller in magnitude than that found by Hazell and Sheldrake for a group of tinnitus patients (who denied hyperacusis) using a combined sound generator and hearing-aid product (McKinney et al., 1999). Larger treatment-related LDL change would be anticipated for hyperacusis patients with hearing impairment using modern combination devices that are now widely available from a variety of manufacturers.

Overview of Our Transitional Intervention Protocol

Based on our understanding of the literature reviewed above and our experience with interventions for decreased sound tolerance and hyperacusis, we devised and patented a transitional intervention protocol for LH (Eddins et al., 2020). Our protocol begins and ends with structured counseling (see Cherri et al., 2024) in which the counselor explains the “vicious circle” of debilitating hyperacusis (Vernon, 2002; Vernon et al., 2002), and the importance of weaning the hyperacusis patient away from self-isolation and sound avoidance toward healthy exposure to comfortable sound levels. This includes weaning the affected patient from counterproductive overuse and overprotection against perceived offending sounds, outwardly manifested by the patient's ongoing reliance on ear-worn sound-depriving HPDs. This counterproductive usage of HPDs in the safety of the quiet home and other similar environments is strongly discouraged in our protocol. The importance of ongoing healthy sound exposure is emphasized in the counseling, with assurance that our protective sound management approach (described below) will enable the patient to be safely exposed to tolerable sound levels in both controlled and uncontrolled sound environments during the intervention. After educating the patient about their hyperacusis condition and explaining the principles and goals of the intervention, protective sound management and therapeutic sound are introduced as our tools for promoting the transitional intervention. The protective sound management is achieved with a bilateral device configuration that ensures the patient's audibility of low-level sounds, while limiting their exposure to potentially offending higher level sounds; this protection is attained by implementing output-limiting compression at levels just above levels of running speech that are judged to be “loud but OK” on a categorical loudness scaling task (Eddins et al., 2024). The output-limiting setting associated with LS is treatment driven by the participant's response to therapeutic sound delivered from low-level broadband sound generators integrated within the ear-worn devices. This neutral therapeutic sound is intended to downregulate abnormally elevated central auditory gain processes, which are widely believed to give rise to LH (see Henry, 2022), thereby restoring neuronal homeostasis and normal gain function within the central auditory pathways (Brotherton et al., 2015). The output-limiting threshold settings are adjusted incrementally in the programmable digital devices per a progressive protocol based on treatment-driven incremental change in the patient's loudness judgments to running speech (Eddins et al., 2024). As the patient's sound tolerance improves with treatment, the treatment-driven adjustment of the output-limiting sound protection allows for incremental exposure to progressively higher healthy sound levels, in turn, leading to an expanded dynamic range. These latter treatment effects would otherwise be impractical to achieve with ongoing use of HPDs alone. In risky, uncontrolled sound environments, the therapeutic sound is offered with the output-limiting sound protection. As the intervention progresses and the patient's sound tolerance improves, reliance on the sound protection is progressively reduced. In controlled sound environments, the patient's use of the low-level sound generators (and low-level household environmental sound sources) is encouraged without the use of protective sound management. Over the course of the transitional intervention, the need for this dual management approach lessens as the treatment increasingly promotes the patient's exposure to and acceptance of safe, healthy, higher sound levels that are essential for establishing and sustaining typical sound tolerance and mitigating primary hyperacusis. Accordingly, these protected and unprotected sound management approaches, together with our therapeutic sound and structured counseling protocols, collectively constitute our transitional intervention for debilitating LH. The implementation and evaluation of this comprehensive strategy is described by Formby et al. (2024) in a 6-month field trial of the transitional intervention. The latter companion report also includes the promising outcomes of that trial, which support the proof of concepts and principles that are the bases of our transitional intervention as reviewed in this report.

Conclusions

This report has reviewed the historical literature and relevant theoretical background that motivate the development of and delineate the rationale for a patented transitional intervention for debilitating LH. Our implementation and evaluation of this intervention are reported in this issue by Formby et al. (2024), who share the promising outcomes from a 6-month field trial. Fully detailed descriptions of the counseling (Cherri et al., 2024) and device and fitting (Eddins et al., 2024) protocols, which were integral to the success for the intervention, also are published in companion reports in this issue. These reports collectively characterize a transitional intervention that offers real potential for meaningful benefit across a broad range of individuals who experience primary hyperacusis and related conditions of decreased sound tolerance.

Funding Statement

The preparation of this report was supported by an award from the National Institute on Deafness and Other Communication Disorders Grant R21DC015054 (awarded to the principal investigators, C. Formby and D.A. Eddins).