Non–organic hearing loss (NOHL) involves inconsistencies in a hearing test that raises suspicions of authenticity. These can be challenging to manage depending on the reason for the evaluation. This literature review located and synthesised existing practical strategies for Australian hearing care professionals (HCPs) working in retail clinics to identify, detect and manage non–organic hearing loss (NOHL). Academic articles between 2000–2020 were reviewed from PubMed and Google Scholar—26 articles were included after preliminary reading. NOHL can be detected to a degree without referring on unnecessarily, by routinely using standard equipment. Recognising the reasons for the audiological evaluation, basic psychological motivations and behavioural indicators in the clinic, assists HCPs to better manage NOHL cases.
Keywords: Non–organic hearing loss, Audiometry, Acoustic Reflexes, Otoacoustic Emissions
In practical terms and from the author’s clinical experience, NOHL is potentially at play when the client’s observed behaviour and reports of hearing loss do not match the results of a hearing test. This paper accepts the Austen and Lynch (2004, p. 450) definition of NOHL “Responses to a hearing test indicating a deficit greater than can be explained by organic pathology”. Different terminology was found across all the articles and in Internet searches to refer to NOHL: pseudohypacusis, aggravation, malingering, psychogenic hearing loss, functional hearing loss, conversion disorder, hysterical hearing loss, factitious disorder and simulation. The contemporary term of ‘non–organic hearing loss’ is used throughout this paper to maintain neutrality and consistency (Austen & Lynch, 2004; Morita, Suzuki, & Iizuka, 2010).
It was hypothesised that NOHL presentations pose challenges for retail HCPs due to its infrequent presentation and lack of knowledge around detecting it. This results in the client being referred back to their medical doctor for further audiological investigation. In Australia, audiology is no longer solely based on a quasi–medical model. Some of the major hearing health clinics are owned by ‘international hearing device manufacturers which operate largely within in a self–regulated industry’ (Standing Committee on Health, Aged Care and Sport [SCHAS], 2017). Clients are commonly seen for audiological evaluations in a retail setting within a “vertically integrated” model (SCHAS, 2017, para. 5.7), which has a primary focus on hearing device sales and fittings over diagnostic tests. Access to some specialised equipment for electrophysiological tests is limited therefore requiring onward referral. Understanding practical strategies to identify and manage these cases is useful and efficient for both the client and HCP. It can also prevent unnecessary referrals and sometimes invasive interventions, for example implant surgery (Drouillard, Petroff, Majer, Perrot, Quesnel, & François, 2014; Mistry, Carr, Tapper, Meredith, Strachan, & Raine, 2016). Detection of NOHL is also important for an HCP to ensure their client management is satisfactory.
This paper focuses on themes that were common across the reviewed literature which may assist the retail HCP. It defines NOHL and provides common referral indicators. Basic psychological motivations associated with NOHL using a model are summarised. Estimated prevalence rates and demographics are provided. A short explanation of the audiogram and degree of loss is followed by a brief outline of auditory physiology. Referral reasons, common behavioural signs and audiometric features are highlighted. Common tests that can be used in a retail hearing clinic to help identify NOHL are then set out.
The questions this paper wanted to answer were: “What are the commonly reported behavioural indicators of NOHL?” and “What practical strategies and tests can HCPs working in retail hearing clinics use to detect and manage NOHL?”.
Academic journal articles in English were sourced through PubMed and Google Scholar, using Boolean search terms between the years 2000—2020 (Table 1). First, 52 articles’ abstracts were read and then narrowed down to 37 articles which included reading the conclusions. Of those, 26 articles were chosen and read in detail to form the literature review base. Individual article quality was assessed through strong relevance to theme as preliminarily defined by its abstract. The search was narrowed and organised into relevance using a scale of low, medium or high with a preference towards puretone and speech audiometry used in conjunction with physiological tests. Duplicate and low–relevance articles were excluded. The Handbook of Clinical Audiology reference textbook (Katz, Chasin, English, Hood, & Tillery, 2015) is a comprehensive guide to audiological practices and was used to summarise some concepts.
Table 1. PubMed and Google Scholar Search Terms and Results
“Nonorganic” + “hearing loss”
“Nonorganic” + “hearing loss” + “pseudohypacusis”
“Malingering” + “hearing loss”
“Functional” + “hearing loss”
1 040 000
“Functional” + “auditory” + “disorder”
“Psychogenic” + “hearing loss”
“Exaggerated” + “hearing loss”
“False” + “exaggerated” + “hearing loss”
The literature concurred with the concept of NOHL as being subjective hearing thresholds that are inconsistent with objective test results. Sixty-nine point two percent of the articles consistently stated that the most common factor in NOHL cases was financial gain, reward or benefit. These also stressed the importance of recognising the reasons for the audiological evaluation and the source of the referral. The prevalence rates were significantly variable, ranging from 0.21% to 90% depending on the population tested. This variance was supported by the issue of financial gain, such as compensation which is commonly involved in NOHL cases, thus distorting the rate. Most authors touched on the basic psychological motivations, with 46.1% referring to the Austen and Lynch model (2004). General observation of a client’s behaviour was a dominant theme in 53.8% of the articles. The majority of articles referred to puretone audiometry (80.7%), acoustic reflex testing (73%) and otoacoustic emissions (69.2%) to test for NOHL. Some articles mentioned that the most common audiometric configuration was flat and sensorineural. Avoiding unnecessary medical intervention was an issue that most articles mentioned. One cochlear implant clinic reported 2% of people being excluded from implant surgery on the basis of NOHL (Mistry, Carr, Tapper, Meredith, Strachan, & Raine, 2016). The literature review included information over a period of twenty years with the bulk of articles older than 2015. There is an opportunity for future researchers to consolidate recent data and compare these against historical information, to assess prevalence for example.
What is NOHL?
NOHL refers to a hearing loss that cannot be explained by organic pathology and is neither supported by objective tests (Georgescu, Stan, Marinescu, & Pǎun, 2014; Saravanappa, Mepham, & Bowdler, 2005). Most authors included a definition which was an interpretation of “NOHL is a decrease in hearing that is unexplained by anatomic or physiologic abnormalities… a disparity between subjective and objective results” (Cullington, 2017, p. 8; Lin & Staecker, 2006, p. 321). Audiometry is usually repeatable and the client’s responses uniform, whereas NOHL responses are variable. The client might show exaggerated responses or no responses at unexpectedly high intensity levels, when they were able to follow normal conversation before the hearing test and the clinical history contains no information to support the results. Essentially, no factor was identified to explain the degree and configuration of the loss (Hiraumi, Tsuji, Kanemaru, Fujino, & Ito, 2007). It is important to note too, that both an organic and non–organic hearing loss component can be present, such as in a noise–induced loss (Lin & Staecker, 2006). Audiometry heavily relies on subjective input from the client which makes these cases more challenging to identify because of underlying motivations for the audiological evaluation.
Underlying Motivations of NOHL
The reason a person presents and who has referred them for an audiological evaluation is important in detecting NOHL (Table 2). Uncovering motivations increases the HCPs requirement to proceed with caution and ensure where necessary that the person is referred on to obtain specialised support.
Table 2. Common Referral Indicators of NOHL
Although it is outside HCPs’ scope of practice to diagnose psychological factors within a NOHL case, a basic understanding assists in effective audiological management and appropriate referral (Austen & Lynch, 2004; Martin & Clark, 2015; Z. Mehta, 2003). There has been discussion about the conscious and unconscious reasons for NOHL since the 1940s (Austen & Lynch, 2004; Morita et al., 2010; Zhao, Dai, Chi, & Wang, 2008). According to the Austen and Lynch hypothesis, there is more psychology involved in some cases which does not limit the reasons to intentional deception (Austen & Lynch, 2004). Their model categorised motivations using a theory of reward and intention (Austen & Lynch, 2004; Lin & Staecker, 2006). It also linked to the Diagnostic and Statistical Manual of Mental Disorders enabling a stronger psychological connection to NOHL.
Although prevalence appeared to vary dependent on the population, 69.2% of the articles consistently stated that the most common factor in NOHL cases was financial gain, reward or benefit (Austen & Lynch, 2004; Durmaz, Karahatay, Satar, & Hidir, 2009; Thompson, 2017). This supported the assertion of prevalence variability between and within populations. Authors’ examples included people applying for disability benefits (Holenweg & Kompis, 2010), head injury compensation (Erdal, 2004; Georgescu et al., 2014) and military contexts (Mehta & Singh, 2000). Where the results of an audiological evaluation may assist a person to obtain a financial benefit, such as compensation, it was strongly recommended that the HCP apply a rigorous test battery.
The second most common reason cited by 46.1% of the articles was associated with avoidance of a duty or situation (Austen & Lynch, 2004; Zhao et al., 2008). This included children manifesting hearing loss because of problems at school and adults experiencing a traumatic incident (Austen & Lynch, 2004). Where the results of an audiological evaluation may assist a person to avoid a duty or obligation, such as military service, it was recommended that the HCP apply a rigorous test.
The third most referenced reason by 42.3% of the articles was associated with emotional gain. The HCP is more likely to refer on for psychiatric help in these cases as the reasons for the hearing evaluation might not be as forthcoming or easy to discover (Austen & Lynch, 2004; Morita et al., 2010).
Table 3 shows prevalence to be variable and ‘dependent on the population of people’ as examined in the literature (Austen & Lynch, 2004, p. 329; Lin & Staecker, 2006, p. 321). The articles included in this review reported prevalence of NOHL as ‘fairly common’ (Mehta & Singh, 2000, p. 79) to ‘not very frequent’ (Musat, Sarafoleanu, & Stelea, 2013, p. 45) with a ‘peak in adults in the early 40s’ (Holenweg & Kompis, 2010, p. 1218).
Prevalence of NOHL in Reviewed Articles
Mean Age in Years
10 – 50 %
General population Compensation or military
6 – 17
Austen & Lynch, 2004, p. 449
10 – 50%
9 – 34%
Balatsouras et al., 2003, p. 518
Cullington, 2017, p. 8
Drouillard et al., 2014, p. 1633
Holenweg & Kompis, 2010, p. 1213
2 – 90%
Lin & Staecker, 2006, p. 321
Dumaz et al., 2009, p. 840
14 – 82
Mistry et al., 2016, p. 2
Morita et al., 2010, p. 444
Adults and children
Psarommatis et al., 2009, p. 1859
Rowan et al., 2012, p. 179
Adults and children
8 – 45%
15 – 20%
5 – 7%
Adults and children
Saravanappa et al., 2005, p. 1235
The Austen–Lynch Model.
The categories of NOHL are named malingering, factitious and conversion, with the underlying motivation plotted across a corresponding spectrum of intent and gain (Austen & Lynch, 2004; Balatsouras et al., 2003; Mistry et al., 2016).
Malingering. Associated with a high level of intent to obtain an external reward (Austen & Lynch, 2004; Lin & Staecker, 2006) whilst being fully aware of their actions (Mistry et al., 2016). This conscious type, commonly referred to as malingering, connotes negativity and intentional deception (Holenweg & Kompis, 2010; Lin & Staecker, 2006); something a person does to cheat the system or obtain something unfairly by pretending (Georgescu et al., 2014). “It is the intentional production of false or grossly exaggerated physical symptoms which is typically motivated by external incentives” (Austen & Lynch, 2004, p. 451).
Factitious. Moves across the spectrum to a lower level of intent and higher internal gain. Factitious was described as “an intentional feigning of physical symptoms to be rewarded psychosocially” rather than pure financial gain (Austen & Lynch, 2004, p. 451). The underlying concept of this disorder in NOHL, is to obtain a reward that is more emotionally based. Such as, being considered sick and cared for by others, facilitating ‘avoidance of self–fulfillment when there is fear of failure’ (Austen & Lynch, 2004). There remains a degree of intention and an element of external gain in this category, albeit, not as high as malingering which is deliberate and overt.
Conversion. The outlier in this model, proposed to be the most pathological of the three variants, even though it was associated with low intention and low external gain (Austen & Lynch, 2004). It was this client who particularly warrants psychiatric intervention and assessment for appropriate care and management (Austen & Lynch, 2004; Holenweg & Kompis, 2010). Although low in reported numbers, these people were the most likely to submit to invasive and unnecessary surgeries such as cochlear implantation (Austen & Lynch, 2004; Saravanappa et al. 2005). Children were thought to be represented in this cohort, in part due to immaturity and reliance on parental involvement, resulting in misdiagnoses (Morita et al., 2010).
Audiogram and Degree of Hearing Loss
An ‘audiogram’ is a graph of frequency and intensity that plots hearing thresholds conducted by puretone audiometry (PTA). It indicates the lowest intensity a person can perceive sound, thus revealing the degree of hearing loss (American Speech Language Hearing Association [ASHA], 2015). Thompson (2017, p.17) reported a widely accepted hearing loss categorisation (in dBHL): normal 0–20, mild 21–40, moderate 41–55, moderately–severe 56–70 and severe between 71–90. Profound hearing loss was determined to be greater than 91. It is these basic audiometry results that are primarily incongruent with observed behaviour that raises HCPs’ suspicions about potential NOHL. The HCP can seek out past audiological evaluations if available for comparison purposes. The authors also emphasised the importance of obtaining a thorough clinical history and asking open questions, whilst observing the client’s body language.
The most common reported audiometric configuration was flat or asymmetrical (Balatsouras et al., 2003; Holenweg & Kompis, 2010) and predominantly sensorineural (Georgescu et al., 2014).
False–positives and False–negatives. The “hallmark of NOHL is the lack of test–retest and inter–test consistency” (Lin & Staecker, 2006, p. 322). A false–negative occurs when the client fails to respond at levels close to the true threshold which is common in NOHL (Balatsouras et al., 2003; Martin & Clark, 2015). False–positives happen when a person responds to no tone being presented and these rates tend to be lower in NOHL cases (Lin & Staecker, 2006) because a “conscientious responder” acknowledges tones that are non–existent at or above threshold (Martin & Clark, 2015, p. 619).
Lack of Shadow Curve. Crossover occurs when sound from one side of the head reaches the other. Interaural Attenuation (IA) influences cross–heard signals (Martin & Clark, 2015). In Australia, the generally accepted IA values for air–conduction are 40dB under headphones and 60–70dB for inserts, depending on the HCPs educational institution. Bone conduction is 0dB, however Steiger (2015, p. 57) accepted up to 15dB at some frequencies. When the IA is exceeded, the contralateral ‘better’ ear should perceive the stimulus, resulting in a positive response from the client. Essentially, a ‘shadow curve’ is representative of the test ear being stimulated but the sound is perceived by the non–test ear. When a unilateral or asymmetrical hearing loss lacks a shadow curve, it is “suspicious” (Al-dujaily, 2015, p. 65; Lin & Staecker, 2006, p. 324; Musat et al., 2013, p. 41). NOHL clients may respond to tones in the better ear and none in the poorer ear. No response, especially to bone conduction, in the absence of contralateral masking is an indicator that the poorer ear’s threshold is likely better than admitted. Contralateral masking was recommended to exclude cross–heard signal whenever appropriate (Thompson, 2017).
Behavioural Indicators of NOHL
HCPs should be aware of signs exhibited by a client during a hearing evaluation that can indicate deception and raise suspicion (Table 4). Observing the client’s general behaviour during the appointment was the strongest indicator found in the literature (53.8%). Exaggerated mannerisms, quality of voice, following conversation at a normal volume or when the speaker is faced away, unnatural lipreading, whispering to another person, asking for repeats, lack of eye contact and nervousness were some of the common indicators (Holenweg & Kompis, 2010; Psarommatis, Kontorinis, Kontrogiannis, Douniadakis, & Tsakanikos, 2009; Thompson, 2017).
However, it is important to balance suspicion with other factors happening on the day—there could be a misunderstanding of the audiometric task, the client is unwell, psychological influences are present or even equipment failure. There are also genuine pathologies that may present as NOHL, such as Auditory Neuropathy Spectrum Disorder (Lin & Staecker, 2006), which is beyond the scope of this paper and covered in depth elsewhere. If faced with inconsistent results, reinstruct and encourage whilst providing positive feedback. Avoid confrontation when explaining results to clients, because the true results rely on the client’s subjective opinion and cannot be conclusively inferred by supposition (Norrix, Rubiano, & Muller, 2017). Most authors recommended that HCPs consider the information that is gained in context from a battery of tests and not rely on an individual one. Cross–check consistency with other tests, including tympanometry and acoustic reflex testing, in conjunction with observing general behaviour (Kreisman, Smart, & John, 2015, p. 119). Confirmation through specialised electrophysiological testing, such as Auditory Brainstem Response (ABR), may be required (Durmaz et al., 2009; Norrix et al., 2017).
Observation of general behaviour
Quality of voice
Responding to non–visual or normal conversation
Asking for repeats, Exaggerated straining to hear,
Lack of eye contact, Whispering ability
Awareness of environmental sound, Cup hand
over ear, Irregular use of hearing aid
Decreased physical movement
Observing the general behaviour of the client provides vital clues regarding hearing acuity. Someone claiming a significant hearing impairment usually results in them speaking loudly. If the quality of voice remains at a normal intensity or they are able to ‘whisper to a companion in the room’, this gives the HCP a hint (Drouillard et al., 2014, p. 1634). Lack of eye contact and discrepancies in observing lip movements which is common in people with hearing impairment was another indicator widely mentioned. Checking the volume and usage of hearing devices can be helpful (American Speech Language Hearing Association [ASHA], n.d; Holenweg & Kompis, 2010). Assess responses when speaking at a normal conversational volume whilst facing away, or from behind was another strategy (ASHA, n.d; Hiraumi et al., 2007). If conversation or environmental sounds, like a ‘telephone ringing in the background’ are heard (Mistry et al., 2016, p. 6) and a normal voice quality is maintained during the hearing test, ensure a rigorous battery is completed.
An uncommon tactic found in the review, was to make an abrupt, loud sound near the client to ‘startle’ them (11.5%). An example is observing the person ‘jump’ at the sound, which would not be likely in cases of severe losses. If it is heard, ‘physical ear movement and eye blinking’ might also be exhibited—the postauricular reflex which occurs in response to abrupt sounds (Benning, 2018; Lin & Staecker, 2006; Musat et al., 2013).
Results of individual tests should not be considered as solely indicative of NOHL. Rather, a battery of tests provides more information helping the HCP to come to an informed and reliable conclusion (Lin & Staecker, 2006). Use a robust yet flexible battery.
Pure Tone Audiometry
Acoustic Reflex Thresholds
Distortion Product OAE
Transient Evoked OAE
Speech Reception Thresholds
Speech Delayed Auditory Feedback
Auditory–Palpebral Test, Doerfler–Stewart
Callhans Voice, Chimani–Moos, Coggins Stethoscope, Erhards, Hummel Double, Swinging Story, Teals, Teuber Two
CON–SOT–LOT, Langenbeck, LING, Rinne,
Tone–in–Noise (TIN), Weber
HCPs can perform a number of tests to detect NOHL in conjunction with tonal and speech audiometry, with ARTs and OAEs dominating the literature (Table 5). The exception was Martin, Martin and Champlin who asserted that although ARTs and OAEs are reliable, they are limited because of ‘equipment requirements and time constraints’ (2000, p. 46).
This is supported to an extent in Australia, where many retail audiology clinics focus on the sale of hearing devices over diagnostic testing (SCHAS, 2017; Han, 2017). Appointment times are generally limited which constrains the examinations to reinforce the provision of hearing devices. The flow–on effect is that some retail HCPs have minimal clinical training in, or knowledge of, OAE interpretation and end up referring on. Regardless of audiology qualification level, educating those HCPs in performing and interpreting OAEs would be beneficial for increasing the range of tests available to detect NOHL in retail clinics. Further, the equipment across these clinics can vary in capability depending on what modules are included. For example, a modern tympanometer brand that is widely used in Australian retail clinics, might be set up to conduct tympanometry only, not ARTs and OAEs. Some ART and OAE modules can be purchased as an add–on to perform these objective tests. Given the low number of NOHL presentations, the return on investment for these added modules and equipment might outweigh their cost, which is one reason retail clinics may choose not to purchase the modules. However, OAEs are regularly used for varying purposes within an audiological test battery in other settings, thus lending support to its equivalent use in retail.
Specialist Referral. The tests outlined here do not propose to negate the requirement to refer to specialists for further tests such as ABR, when results are simply ‘inconsistent’ or support suspicions of NOHL. The HCPs role is to obtain the hearing thresholds as accurately as possible without failing to account for other reasons that contribute to NOHL, which may or may not be organic. Austen and Lynch supported ‘detecting NOHL in early stages and acknowledging the requirement to refer for medical and psychological assessment’ (2004, p. 454). It is important for implant clinics to be made aware of the potential NOHL to help to avoid ‘surgical risk and permanent hearing loss’ (Drouillard et al., 2014, p. 1633; Mistry et al., 2016, p. 1). This awareness is passed on when reports are provided to the medical practitioner from the HCP.
Although there is “not one method that predicts hearing loss without error” (Al-dujaily, 2015, p. 65), ABR is considered to be the “gold standard” (Al-dujaily, 2015, p. 67; Durmaz et al., 2009, p. 841). However, it cannot provide exact thresholds (Mahdavi & Peyvandi, 2006; Morita et al., 2009; Norrix et al., 2010) and is beyond the scope of this paper and covered extensively elsewhere. The six prevailing tests which were administered in the articles are briefly explored below.
Test Order. Individual HCPs and audiology clinics likely have a preferred routine for evaluating hearing loss or follow Audiology Australia’s Clinical Standards (2013, p. 63). If NOHL is suspected, begin with the objective tests (Figure 1). These provide information that is not reliant on the client’s subjective involvement and reduces the need to work backwards to rule out NOHL (Kreisman, Smart & John, 2015). Lateral Thinking is useful on occasion. For example, using variations and alternative techniques within some flexible tests, such as audiometry, further supports conclusions when faced with a challenging NOHL case. Reinstructing without judgement, gently pointing out the results were inconclusive or inconsistent can help. Demonstrating hearing devices under Real Ear Measurements that are set to prescription targets based on the hearing test results to observe a client’s reaction and body language.
Figure 1. Suggested test battery order. Adapted from Katz, Chasin, English, Hood & Tillery, 2015, pp. 122, 626.
The majority of articles (80.7%) favoured using PTA as a basis for measuring hearing threshold levels, which was unsurprising given its long history. The Hughson–Westlake method is a widely used method of assessing hearing threshold levels to produce an audiogram. It consists of a series of puretones presented one at a time unilaterally in a descending–ascending manner which relies on the positive or negative responses from the client before proceeding to the next presentation. The main issue that an HCP may encounter using this method, is the high reliance on the client’s subjective input and their ability to manipulate loudness perception and adjust responses accordingly. Thompson’s study showed the two most used strategies in ‘malingering participants’ (2017, p. 2). One was maintaining a consistent interval between responses and the second was comparing the tones to the participant’s perception of what was ordinarily a soft, average and loud sound. A modified ascending technique instead of the Hughson–Westlake method, improved thresholds between 34.5–36dB (Balatsouras et al., 2003). Where there is a difference between ascending and descending technique results in the puretone average of 5dB or more, consider NOHL (Martin et al., 2000; Musat et al., 2013).
When performing audiometry with a NOHL client, try ‘jumping’ between traditional frequency sequencing to limit anticipation and familiarity (ASHA, n.d). In some cases, it may be helpful to start at a different frequency, use a warble stimulus, change between ears regularly or even put a low level of masking in one ear intermittently during the test. Lengthening the duration of tone stimulus and increasing the interval times between presentations assisted in improving thresholds (Balatsouras et al., 2003; Martin & Clark, 2015).
This useful test can be performed relatively easily in a retail audiology clinic because of the accessibility to standard equipment. The majority of articles (73%) mentioned the usefulness of ARTs. Psarommatis et al. (2009, p. 1860) cautioned against “relying on this for threshold determination” because of physiological variances, which was strongly supported by Al-dujaily (2015). The bilateral reflex occurs at high intensities essentially increasing acoustic impedance. The ART is generally 70–95dB above the 3 Frequency Average Hearing Level (3FAHL) or ‘puretone average’ in normal hearing ears (Al-dujaily, 2015; Musat et al., 2013; Zhao et al., 2008) although it can be “absent in a small number” of this population (Mistry et al., 2016, p. 6). It can also be limited in the presence of an organic sensorineural hearing component due to cochlear recruitment (Balatsouras et al., 2003; Martin & Clark, 2015). The difference between ipsilateral and contralateral acoustic reflex thresholds are between 5–10dB.
Physiology of ART. The physiology enabling this reflex is controlled primarily by the lateral superior olivary which determines the relative intensity of sound stimulus. It controls efferent fibres to the olivary cochlear bundle triggering prestin in the outer hair cells lengthening the cell and reducing the action potentials, to protect against loud sounds. The reticular formation activates the facial and trigeminal nerves which lead to the middle ear via efferent pathways. The facial nerve enervates the stapedial muscle that is connected to the stapes. This muscle contraction restricts the movement of the stapes on the oval window (Feeney & Schairer, 2015). The trigeminal nerve leads to the tensor tympani, attached to the medial part of the malleus, contracting the muscle thus tightening the tympanic membrane, dampening sound stimulus by stiffening the ossicular chain. The contractions result in a change in compliance of the tympanic membrane indicating the loud stimulus was processed by the auditory system (Lin & Staecker, 2006).
A reflex is not usually present with hearing losses greater than the moderately–severe degree, if it is, this test further supports the possibility of NOHL. If the reflex is present within 5–10dB sensation level below (louder) the hearing threshold, it can indicate NOHL (Lin & Staecker, 2006; Martin & Clark, 2015). If the ART is elicited above (softer) the purported hearing threshold, it should be taken as a strong indication of NOHL (Al-dujaily, 2015; Thiagarajan, 2012).
OAEs are low–intensity sounds generated by the stereocilia in the outer hair cells of the cochlea which are measured in the external auditory meatus (Balatsouras et al., 2003; Lin & Staecker, 2006; Prieve & Fitzgerald, 2015). Hearing loss caused by damage to the outer hair cells results in a reduction in or absence of OAEs (Al-dujaily, 2015). OAEs do not evaluate the integrity of the inner hair cells or neural transmission (Durmaz et al., 2009; Lin & Staecker, 2003) nor are they a substitution for puretone audiometry as they do not provide hearing loss degree or type (Rasetshwane, Fultz, Kopun, Gorga, & Neely, 2015).
This electrophysiological test is objective and non–invasive, which broadly assesses cochlear function in the absence of middle ear pathology or ear canal obstruction. Two common evoked OAEs are Distortion Product Otoacoustic Emissions (DPOAEs) and Transient Evoked Otoacoustic Emissions (TEOAEs). Both are expected to provide results where the hearing thresholds are 30dBHL or better. The majority of authors (18 / 26 or 69.2%) supported using OAEs (with 6 / 18 indicating a preference for TEOAEs and 3 / 18 for DPOAEs). These are relatively uncontroversial and have had the benefit of years of testing so enjoy a high acceptance within the clinical community. Rasetshwane et al. (2016) contended that both methods provide reliability and high sensitivity in normal hearing ears, however it is dependent on the stimulus level and frequency.
TEOAEs. Uses a short click or tone–burst wideband stimulus between 1–4kHz, measuring emissions between the clicks, which stimulates a greater area of the basilar membrane of the cochlea (Rasetshwane et al., 2015). TEOAEs are not usually present in hearing losses greater than 30–40dBHL and provide a weaker correlation to the puretone audiometry results (Al-dujaily, 2015: Morita et al., 2010; Rasetshwane et al., 2015).
DPOAEs. Presents two puretones simultaneously between 1–10kHz (equipment dependent) and the emissions are measured during the stimulus presentation and are not usually present in hearing losses greater than 40–50dBHL (Durmaz et al., 2009; Rasetshwane et al., 2015). DPOAEs provide better frequency–specific indications above 1kHz and have a stronger correlation to the puretone audiometry results (Balatsouras et al., 2003; Rasetshwane et al., 2016).
A speech test assesses the ability of a person to understand and discriminate speech. There are two important factors involved with the intensity of a speech signal and the listener’s ability to both detect and understand (Schlauch & Nelson, 2015). The Speech Reception Threshold (SRT) is the lowest intensity that a person can understand and detect 50% of spondaic words correctly. It is used to cross–validate the audiogram and a person with normal hearing should score close to 50% correct at 30dBHL (Lin & Staecker, 2006; McArdle & Hnath-Chisolm, 2015). Half of the reviewed authors favoured this test. In NOHL cases, the SRT is typically better than the 3FAHL, indicating disparity. Thompson’s study (2017) supported this assertion with over 86% of participants having a significantly better SRT than 3FAHL.
Agreement with Puretone Average. The 3FAHL, or puretone average, is calculated as the average of the air–conduction thresholds at 500Hz, 1kHz and 2kHz for each ear. The 3FAHL should agree closely with the SRT (Al-dujaily, 2015). Kreisman et al. (2015, p. 120) recommended using a two-frequency hearing level average for sharply sloping or rising audiograms, to prevent SRT being better than PTA.
Acceptable Variance. The literature revealed a small variance of acceptable limits between the 3FAHL and SRT, of 10–20dB. Georgescu et al. (2014) stated the puretone average should be within 10dB, whereas Schlauch et al. supported 12dB (2015), Lin and Staecker (2006) and Holenweg and Kompis (2010) accepted 15dB of the SRT. Drouillard et al. (2014) allowed a 20dB difference which was the largest variance found in the literature. The majority however, applied 10dB.
The majority of authors favoured the Stenger test, which can be used in asymmetrical losses (of no less than 10dB–40dB) or unilateral losses (Durmaz et al., 2009; Martin & Clark, 2015; Norrix et al., 2017). The combined reliability of sensitivity, specificity and predictive value was reported to be between 70–99.4% (Durmaz et al., 2009; Georgescu et al., 2014). It is an effective, useful test for NOHL, yet seems to be underused in this country. When two sounds of the same frequency but at different intensities are presented simultaneously, the brain perceives one central sound as a result of “binaural fusion” which localises to the better ear (Lin & Staecker, 2006, p. 322; Martin & Clark, 2015, p. 617; Norrix et al., 2017, p. 1). It can be performed using tuning forks, but the contemporary method is via a two–channel audiometer under headphones or inserts.
Positive or Negative Stenger. The literature revealed a small variance of the initial presentation level. Authors recommended between 5–20dB (Durmaz et al., 2009; Musat et al., 2013). In a screening Stenger, the first presentation level is generally 5–20dB softer than the purported threshold in the poorer ear and 5–20dB louder than the threshold in the better ear. Both tones are suprathreshold—the tone is louder than the true threshold of the poorer ear which prevents the better ear from hearing the tone (Martin & Clark, 2015; Norrix et al., 2017). Usually, the NOHL client will not respond, because they are trying to maintain that they have a poorer hearing ear (Norrix et al., 2017).
A ‘positive Stenger’ means the client did not respond, which indicates the tone was heard in the poorer ear, because the tone lateralised to the best ear. A ‘negative Stenger’ is obtained when the client acknowledges the tone, indicating it was perceived in the better ear and is considered an appropriate response. The Stenger test can use either puretones or speech and the same principles apply to speech as to tonal stimuli (Martin & Clark, 2015).
The greatest limitation of the Stenger test is that it cannot be used in symmetrical hearing losses. Rowan, Morris, Adewale and Millgate (2012) studied a Tone–in–Noise (TIN) test which can be used in bilateral NOHL. It compares PTA under ipsilateral narrowband masking, i.e., the tone and masking is presented in the same ear. The concept was that ‘supra–threshold noise would interfere with a subject’s judgement when feigning’ (Rowan et al., 2012, pp. 179, 182). A limitation here is the potential of the masking to cause a threshold shift. A simple test similar to the TIN that can be used in bilateral symmetric losses, would be helpful for the HCPs toolkit. Further research in this area would be highly beneficial in identifying NOHL.
Although only 38.4% of the articles mentioned tympanometry, it was included given its close association to the ART and the equipment that is used. Tympanometry is a commonly used test in retail audiology clinics. It is an objective, physiological measure of acoustic admittance and impedance of the middle ear which is graphically depicted. The pressure variance causes the tympanic membrane and ossicles to flex and stiffen, demonstrating increased and decreased admittance to sound energy. Peak admittance is greatest when middle ear pressure is equal to the atmospheric pressure. Tympanometry is an indicator of middle ear pathology which might impact the PTA results. The HCP can be more informed about this possibility before proceeding to PTA and better able to account for its involvement. There are longstanding accepted types and norms for tympanometry which are associated with various middle ear conditions (Hunter & Sanford, 2015).
The literature review provided strategies for HCPs working in retail audiology to identify NOHL by being aware of a client’s behaviour and motivation in conjunction with audiometric results. Financially motivated clients are cause for a ‘red flag’ alerting the HCP prior to audiometry. Balancing caution and suspicion can be difficult, depending on the individual circumstances as not every case is NOHL. Lateral thinking is helpful when considering how to modify test methods and sequence. Discrepancies between subjective tests and associated behavioural cues can be explained by performing both ARTs and OAEs in the clinic. Upskilling HCPs in the interpretation of OAEs as well as providing them with the required equipment is crucial to completing a full test battery. Two areas of future research proposed in this paper were for a fast and easy test for a bilateral, symmetrical NOHL and the other, to compare current data against historical prevalence rates. Using a robust yet flexible test battery reduces unnecessary interventions and informs other health professionals to possible underlying issues. As a result, efficiency for both the HCP and client is improved and the potential for unnecessary referrals can be reduced.
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