Role of Auditory Training for Hearing Loss

Beyond hearing aids, is there a role for Auditory Training? – A Systematic Review

Hearing loss has been described as an invisible disability and currently affects over 466 million people worldwide, not surprisingly this number increases significantly in people of the age of 65 with one in every three people being affected by hearing loss.  It is estimated that by 2050 this number would have nearly double to over 900 million or one in every ten people worldwide being affected by a disabling hearing loss (World Health Organization, [WHO], 2019).  The impact of hearing loss is far reaching and includes not only significant difficulties in communication tasks, but also social, emotional and economic burdens.  Often, ironically, it is suffered in silence, with people withdrawing from social interaction due to an inability to communication affectively (Dalton et al., 2003).  With hearing impairment being linked to social and emotional isolation, cognitive decline, quality of life issues and general well-being (Hickson et al., 2008; Mick, Kawachi, & Lin, 2014) it is even more important that individuals with hearing impairment are provided with a rehabilitation solution that is more holistic in its delivery and provides optimum outcomes.

Traditionally the most common form of intervention for people with hearing loss is amplification provided by either hearing aids or some form of assistive listening device. 

Hearing aids can amplify the input sound pressure level of acoustic signals, improving the hearer’s detection of sounds which has been affected by peripheral hearing loss. However, as mentioned, peripheral hearing loss is the only one aspect of age-related hearing loss, and therefore also only one of the aspects which result in the oral communication difficulties observed in older adults.9 This is probably one of the fundamental reasons why around 15%–20% of older adults using hearing aids are dissatisfied with the results obtain and approximately 5% to 15% of hearing aids end up in the draw (MarkTrak Kochkin) do not continue to use them. Cardemil, F., Aguayo, L., & Fuente, A. (2014). Auditory rehabilitation programmes for adults: what do we know about their effectiveness?. Acta Otorrinolaringologica (English Edition), 65(4), 249-257.

The most common complaint expressed by adults with hearing loss is the inability to understand a speaker when listening in an environment of background noise. Katz, J., Chasin, M., English, K. M., Hood, L. J., & Tillery, K. L. (Eds.). (1978). Handbook of clinical audiology.

Speech comprehension is one of the problems which are most commonly present in older adults, especially when there is background noise or reverberation

Auditory training can be defined as formal listening activities whose goal is to optimize the activity of speech perception (Dr. Arthur Boothroyd) Boothroyd, A. (2010). Adapting to changed hearing: the potential role of formal training. Journal of the American Academy of Audiology, 21(9), 601-611.

Auditory training aims to increase auditory skills to enhance the individual’s ability to pick up the acoustic cues required for acquisition of auditory skills. 

Hassan, S. M., Hegazi, M., & Al-Kassaby, R. (2013). The effect of intensive auditory training on auditory skills and on speech intelligibility of prelingual cochlear implanted adolescents and adults. Egyptian Journal of Ear, Nose, Throat and Allied Sciences, 14(3), 201-206.

Auditory training aims to compensate for degradation in the auditory signal and is offered as an intervention to help alleviate the most common complaint in people with hearing loss, understanding speech in a background noise (Ferguson, M., & Henshaw, H. (2015, November). How does auditory training work? Joined-up thinking and listening. In Seminars in hearing (Vol. 36, No. 04, pp. 237-249). Thieme Medical Publishers.

  The results of this systematic review should provide information to adult rehabilitation clinicians regarding the efficacy of including some form of auditory training in their clinical practice.

The primary aim of this systematic review is to analyse existing research and determine if the inclusion of auditory training in an aural rehabilitation program provides additional benefit to adult hearing aid wears compared to rehabilitation programs that provide hearing aids alone. 

Methods

Types of studies

The studies selected for inclusion in this systematic review were those that used a high level of evidence and included randomized control trials, within group repeated measures or before/after with control group, all other research designs were excluded from this evidence-based search. 

Types of participants

Participants in the studies selected were required to be adults (≥ 16 years old) with postlingual bilateral sensorineural hearing loss.  For inclusion the reported pure tone average was required to be greater than 25dB hearing level (HL) in the better ear averaged across three frequencies (500Hz, 1000Hz and 2000Hz), pure-tone thresholds no better than 40dB in the better ear at either 1000Hz or 2000Hz or the description of the hearing loss was noted as mild to moderate, which WHO (2013) defines as being – mild 26 to 40dB HL or moderate 41 to 60dB HL.  All participants where currently wearing hearing aids and were either new or experienced users. 

Types of interventions

The accepted methods of AT intervention included were computer-based software packages performed on-line or programs delivered via DVD at home. Participants performed intervention tasks that required them to use either analytic training (bottom-up) which focuses on individual sound recognition and words rather than whole sentences or synthetic training (top-down) which involved approaches such as improved hearing attention, use of context and repair strategies that focus on gaining enhanced meaning of the message (Ross, 2011) or a combination of the both tasks. 

Types of outcome measures

Outcome measures performed in the selected studies were either behavioural or electrophysiological measures or a combination of both.  The primary outcome measures collectively used across all studies were: Words in Noise Test (WIN) (Wilson, Carnell & Cleghorn, 2007), Revised Speech in Noise (R-SPIN) (Bilger, Nuetzel, Rabinowitz, & Rzeczkowski, 1984), Hearing in Noise Test (HINT) (Nilsson, Soli & Sullivan, 1994), Connected Speech Test (CST) (Cox, Alexander & Moore, 1987), Rapid Speech Test (RST), Competing Word Test (CWT), Digital Span (DS), Speech in Noise Test (SIN), Memory for Verbal Sounds (MVS), Memory for Nonverbal Sounds (MNVS), Word Recognition Score Tests (WRS), Synthetic Sentence Identification (SSI) (Speaks & Jerger, 1966), sound localization, speech perception test, cognitive test and electrophysiological testing. Secondary outcome measures were subjective in nature and looked a patient reported outcomes for both hearing and health quality of life, these included: Abbreviated Profile of Hearing Aid Benefit (APHAB) (Cox & Alexander, 1995), Hearing Handicap Inventory for the Elderly (HHIE) (Ventry & Weinstein, 1982), Communication Profile of Hearing Impaired (CPHI) (Demorest & Erdman, 1987), Device Oriented Subjective Outcome Scale (DOSO) (Cox, Alexander & Xu, 2009).  

Search Strategy

This systematic review of literature followed guidelines explained by Perestelo-Pérez (2013).  A comprehensive investigation was undertaken by means of a computerised database search in PubMed, Medline, Google Scholar, ScienceDirect and Microsoft Academic. A combination of the following key words was used to conduct the search: “adult” and “hearing impaired” or “hearing loss” or “hearing aids” or “hearing difficulties” and “auditory training” or “aural rehabilitation” or “auditory rehabilitation” or “communication training” or “hearing training”.  Limiting factors for the search were adult participants and publications in English language, no restrictions were placed on year of publication. 

Selection of Studies

A total of thirty-two articles were identified during the computerized database search and a preliminary review of article abstracts was undertaken with regards to selection criteria. Fourteen articles were eliminated following this initial review of abstracts, with the remaining articles retrieved and evaluated thoroughly.  Following this detailed review, a further thirteen were eliminated based on inclusion criteria leaving five articles to be reviewed.  Figure 1 is a flow chart which provides information regarding the process of exclusion.

Data Extraction

The information extracted from the studies included: study design, methods of randomization and blinding, inclusion and exclusion criteria, type of intervention and control, outcome measures and statistical tests.  For both the intervention and control groups, data extraction included: participant characteristics (number, sex and age), details of their hearing loss (mean, standard deviation or range) and participant adherence to the training intervention.  Where available for both the intervention and control groups, further information was extracted that related to participants experience with hearing aid use and hearing aid information (bilateral or monaural hearing aid fittings, style of device fitted, prescriptive fitting formula and fitting verification procedure used if reported). 

Assessment of Quality and Risk of Bias

Six measures where used to assess study quality and methods adopted to minimize bias: control group, level of evidence (study design), blinding, power calculations, validated outcome measures, inclusion/exclusion criteria and participant drop out.  Measures were rated as either meeting criteria, not meeting criteria or information not available and are summarized in Table 2.  Three of the five studies were randomized control trials (Bock & Abrams, 2014; Gil & Iorio, 2010; Saunders et al., 2016), which offer the highest level of evidence, four reported inclusion of a control group (Bock & Abrams, 2014; Gil & Iorio, 2010; Kricos & Holmes, 1996; Saunders et al., 2016) and only one study incorporated blinding (Gil & Iorio, 2010).  Due to differences in heterogeneity between the studies in regards to training protocols, outcome measures implemented and participant variables, it was not possible to group results across all studies and a narrative synthesis is provided to assist with elucidation of outcomes across the five studies in this review.

Results

  Table 1 provides a summary of information extracted from each of the five studies and includes study design, participants, interventions used, outcome measures and results.  There was a total of 430 participants across the five studies with ages ranging from 16 to 85 years.  Only one study included younger participants aged 16 years and older (Gil & Iorio, 2010), with the other four studies (Bock & Abrams, 2014; Henshaw & Ferguson, 2013; Kricos & Holmes, 1996; Saunders et al., 2016) focusing on older participants aged 60 years or above. Only one study had a sample size of over 40 participants (Saunders et al., 2016) per group, with the other studies varying from 7 to 30 participants per group.  Kricos & Holmes (1996) was the only study that provided information regarding gender and included a fairly even distribution of both males and females in the study with similar demographic information.  All of the studies included participants that were currently wearing hearing and one study separated hearing aid wearers into either new users (worn hearing aids < 6 months) or experienced users (worn hearing aids for > 6 months) (Saunders et al., 2016).  Other inclusion criteria commonly applied across studies was that participants had a sensorineural hearing loss described as mild to moderate, have English as their first language, have corrected vision and have no evidence of dementia or cognitive disturbance.

Training interventions, number of training sessions and training period varied considerably across the five studies.  Two studies employed analytic training that involved verbal repetition, pointing to sentences, figures and completing puzzles (Bock & Abrams, 2014; Gil & Iorio, 2010) and three studies focused on an intervention with both analytic and synthetic training (Henshaw & Ferguson, 2013; Kricos & Holmes, 1996; Saunders et al., 2016).  Two of the studies involved training programs totally eight hours which was completed over a four week period and was made up of an hour session performed twice a week (Gil & Iorio, 2010; Kricos & Holmes,1996).  Another study varied slightly from this with a total of ten and a half hours of training across a three week period involving thirty minutes of training each day (Bock & Abrams,2014) and one study had a much shorter training period, only 7 days with a total of three and half hours training which consisted of two fifteen minute sessions per day (Henshaw & Ferguson, 2013).  One study had training programs that varied across the two intervention groups, with one group receiving a total of five hours training delivered over two weeks with five thirty minute sessions a week and the other received a total of ten hours training over four week with five thirty minute sessions a week (Saunders et al., 2016).

Compliance to the training programs was reported by three of the five studies, with Bock & Abrams (2014) recording very low compliance, only four of the fourteen participants completing the full training task of 630 minutes and one participant in the intervention group did not completing the program.   Henshaw and Ferguson (2014) did not indicate dropout rate by participants in the study, but reported the average time the participants spent on the training task was 197.8 minutes which was less than the 210 minute required to complete the intervention program design.  Saunders et al. (2016) indicated that compliance was measure differently across the two intervention groups.  The LACE-DVD relied on patient reported compliance which was approximately 85% following completion of the ten sessions.  For the LACE-C group data was accessed from the LACE server and of the 65 participants in this group data was retrieved from 50 and compliance was 84%, with 42 completing all 20 training sessions.  Compliance with the training program and participant dropout rate was not reported in the studies performed by Gil and Iorio (2010) or Kricos and Holmes (1996).

Outcome measures varied across all studies and include a combination of behavioural measures, electrophysiological evaluations and self-reported questionnaires and the results can be seen following review of Table 1.  All studies implemented at least one of the following validated speech in noise tests (SIN, WIN, R-SPIN, CST, HINT or MCRM) with all except for one (Saunders et al., 2016) reporting statistically significant improvements following AT intervention.  Kricos and Holmes (1996) study included two treatment groups, one underwent analytic AT and the other active listening training.  Speech recognition was measured using CST under two conditions, auditory alone and auditory-visual, compared to the analytic and control group, the active listening group showed improvement in speech recognition post training for auditory-visual condition.  Two studies reported significant improvement in speech in noise on the HINT and WIN (Bock & Abrams, 2016) and SIN (Gil & Iorio, 2010) for the intervention group following treatment.  Henshaw and Ferguson (2013) study showed a significant main effect of time on speech reception thresholds using the MCRM.  The also reported results for on-task learning and found highly significant main effect of both block and phoneme discrimination over time, suggesting generalisation of on-task learning. 

A number of studies reported on measures of self-reported hearing handicap with Gil and Iorio (2010) demonstrating an improvement in reverberation and background noise sub-scale on the APHAB following AT intervention.  Kricos and Holmes (1996) demonstrated a significant main effect for the verbal, nonverbal and behaviour subscale in the active listening group as measured by the CPHI, but did not find any treatment effects when using the HHIE to assess self-reported hearing difficulties.  Both Bock and Abrams (2016) and Saunders et al. (2016) investigated hearing handicap measured by using the APHAB and found no significant improvement post training between groups.  Bock and Abrams (2016) also measured hearing aid outcome using the DOSO and again found no significant improvement post training between groups.  Only one study reported on electrophysiological evaluations (Gil & Iorio, 2010) and found a statistically significant reduction in P3 latency in the experimental group when comparing pre and post training evaluations.

Discussion

We cannot exclude the possibility that other studies have been published showing positive or negative results, which have not been included here, but we are confident that the extensive electronic search and subsequent reference checking has captured most of the relevant literature. However, we invite readers to notify us of any trials or studies we may have missed so that they might be included in subsequent updates to this review. Similarly, although we did make efforts to contact study authors directly to clarify study methods and obtain raw data where possible, we were not always able to do so. We would very much welcome contact from any of the authors cited in this review who feel that their data could be included in the meta-analysis in future updates.  Some of the studies were excluded on the basis that their outcomes did not meet the inclusion criteria for this review. As far as we are aware, based on an assessment of the methods sections of these studies, the relevant outcomes were not available because they were not measured. However, it is possible that other outcomes were measured and not reported. We invite the authors of these studies to contact us if additional outcomes, which could be included in future updates, were measured but not reported.  Two review authors independently selected trials, extracted data, assessed risk of bias and graded the quality of evidence in order to minimise bias in the review process.  None of the review authors had any involvement in any of the trials. This has not been the case in some previous systematic reviews in the context of hearing healthcare.

P3 latency which has been reported to occur when completing tasks that require attention to stimulus (Foss-Feig, Stone, & Wallace, 2012).

auditory training can alter the preconscious neural encoding of complex sounds by improving neural synchrony in the auditory brainstem (Russo, N. M., Nicol, T. G., Zecker, S. G., Hayes, E. A., & Kraus, N. (2005). Auditory training improves neural timing in the human brainstem. Behavioural brain research, 156(1), 95-103.)

This review aimed to look at long-term outcomes as hearing loss is a long-term condition requiring self-management on the part of the patient over many years. Only six of the studies we

identified looked at outcome over one year or longer (Andersson 1994; Andersson 1995; Cherry1994; Chisolm 2004; Oberg2008; Oberg 2009), and only two of these addressed the primary outcome of hearing aid use (Oberg 2008; Oberg 2009) (see Summary of findings 3)

Due to the nature of the interventions in this context it is difficult to design studies that are blinded to participants and those delivering the intervention so performance bias is difficult to control for.

A strength of the studies we identified is that they had low dropout rates even for long-term follow-up periods of over a year and there were only occasional instances of unexplained losses to follow-up.  With a few exceptions, studies were small and lacked power calculations. Some studies were funded by hearing aid manufacturers, although this should not introduce undue bias as both control and interventions groups were provided with hearing aids in all cases.

References

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