Hearing loss is a globally prominent health condition, which is especially prevalent in the older population. Untreated hearing loss is known to cause communication problems, which might result in social isolation, depression, and reduced quality of life (Morris et al. 2013; Davies et al. 2017). Auditory rehabilitation aims to enable an individual with hearing loss to regain the ability to hear and actively communicate. Auditory rehabilitation requires the active participation of the individual, including the decision on how rehabilitation can be achieved (Boothroyd 2007). The most common intervention for auditory rehabilitation from sensorineural hearing loss is hearing aids (Chisolm et al. 2013; Ferguson & Henshaw 2015). However, it is estimated that a large proportion of persons that would benefit from hearing aids are currently not using amplification (Davies et al. 2017). Another issue is that, despite the technical achievements over the past years, amplification by hearing aids alone does not prevent elderly individuals with hearing impairment from struggling in difficult listening situations (Humes et al. 2009a; Kaplan-Neeman et al. 2012). A potential underlying cause could be reductions in cognitive abilities such as memory performance, speed of processing, and executive functions that are relevant for everyday communication and that are known to occur in individuals with peripheral or central hearing loss (Lin et al. 2011a,2011b; Fulton et al. 2015). Thus, additional rehabilitation strategies are needed that increase the acceptance of hearing aids and the success of auditory rehabilitation.
A complementary option that is used to support rehabilitation is auditory training (AT). By actively training auditory skills, individuals learn to make perceptual distinctions of sounds with the goal to increase communication skills (i.e., speech perception) (Henshaw & Ferguson, 2013; Olson, 2015). Structured AT is often used as a self-management tool during auditory rehabilitation, adapted toward the need of the individual (Dubno 2013; Henshaw & Ferguson 2013; Olson et al. 2013; Ferguson & Henshaw 2015). Several AT programs are commercially available.They are computer-based and can be easily accessed through the internet, or on a personal computer with software installation. Examples for AT programs are: BrainHQ (Posit-Science), Listening and Communication Enhancement (LACE; Neurone), or clEAR (clEAR LLC). AT programs are often game like and should not be tedious for the patients to ensure their compliance. An advantage of structured, computer-based AT programs is that individuals can train at home and only need to see the clinicians/hearing care professionals at regular appointments to monitor effects of training (Tye-Murray et al. 2012; Henshaw & Ferguson, Reference Note 1; Henshaw et al. 2015). The effect of training is assessed by measuring the performance on the trained tasks (on-task learning). A generalization of learning toward a more real-world like benefit of training should be assessed by testing performance in untrained tasks (Wright & Zhang 2008; Henshaw & Ferguson 2013). Generally, to assess the actual training effect, it is important to compare the performance of the intervention group with a nontraining or placebo-training group in a randomized control trial (RCT) to rule out other confounding factors.
Evidence from studies published in recent years supports the idea that AT might be a tool to improve speech perception and other auditory cognitive skills in individuals with hearing impairment (with and without hearing aids) and cochlear implant users (for a review cf. Henshaw & Ferguson 2013). A recent review and meta-analysis suggests that auditory and cognitive training in individuals with hearing impairment can additionally improve cognitive skills such as working memory and overall cognition (Lawrence et al. 2018). Hence, training auditory and cognitive skills in combination with amplification seem to be one option to enhance auditory and cognitive rehabilitation and therefore to enhance communication skills in elderly individuals with hearing impairment (Henshaw & Ferguson 2013; Anderson & Jenkins 2015; Lawrence et al. 2018). However, previous research showed that the outcome of AT studies varied substantially and that a generalization of training benefit is not consistently measurable (Henshaw & Ferguson 2013).
Aim and Research Questions
The aim of this state-of-the-art review was to summarize and discuss current evidence on AT in the process of auditory rehabilitation published after the systematic review by Henshaw and Ferguson (2013). This present review focused on improvements in auditory outcome measures, specifically speech perception abilities, after intensive auditory or auditory–cognitive training, which is in contrast to a recent review and meta-analysis by Lawrence et al. (2018). Lawrence et al selected and analyzed studies for their review and meta-analysis that used cognitive outcome measures. An improvement in auditory performance was not assessed in the work of Lawrence et al. In addition, in the present state-of-the-art review, only RCTs were included. Therefore, only four out of the 16 studies in this review overlap with the review by Lawrence et al (see Table Supplemental Digital Content 1, http://links.lww.com/EANDH/A579: Anderson et al. 2013; Ferguson et al. 2014; Abrams et al. 2015; Saunders et al. 2016). A critical reflection on current standards and future research perspectives is included in the Discussion.
The target group of this state-of-the-art review was individuals with hearing impairment, with and without hearing aids, and including novice and experienced hearing aid users. To get a valid picture on the effectiveness of AT, only studies measuring training effects on untrained tasks in comparison to a control group were included. A meta-analysis of the compared studies did not seem appropriate as the studies were highly heterogenous in terms of samples size, participant groups (mixed group of individuals with normal hearing and individuals with hearing impairment, individuals with hearing impairment versus individuals with normal hearing versus individuals wearing hearing aids), training setup (duration and type of training), and chosen outcome measures. For the current review, the reporting of findings is a narrative approach to interpret the effectiveness of AT based on the outcome of the selected 16 studies.
MATERIALS AND METHODS
Generally, state-of-the-art reviews focus on the most recent literature and point out priorities for future research (Grant & Booth 2009). Guidelines from the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement were used to report about selected studies (Moher et al. 2009). Only articles published between December 2012 and December 2018 (last search was conducted on December 7, 2018).
The participant, intervention, control, outcome, and study design (PICOS) criteria (Moher et al. 2009) were used to define inclusion and exclusion criteria for the revealed articles.
- Participants: adults with hearing impairment; severity of hearing impairment was defined to be mild to moderately severe; groups with or without hearing aid intervention were included.
- Intervention: intensive auditory or auditory–cognitive training programs with one or more training sessions per week over several weeks. AT included training on auditory stimuli such as tones, phonemes, vowels or consonants, words, or sentences. Some training protocols involved audiovisual stimuli. Other forms of training were defined as auditory–cognitive, which is a more hybrid form of auditory and cognitive training. Trained tasks included auditory tasks, cognitive tasks (e.g., working memory or attention training), as well as training on communication strategies.
- Control: comparison to a control group either undergoing placebo training, hearing aid fitting without further intense training, or no training.
- Outcome: one or more objective outcome measures related to speech perception. Subjective improvements (self-reported communication improvement) were considered only in combination with objective outcome measures.
- Study design: RCT or pseudo-RCTs, non-RCTs, repeated measures including the comparison to a control group.
Furthermore, only studies published in English and in peer-reviewed journals were included. Studies investigating children, cochlear implant users, or tinnitus patients were excluded for the current state-of-the-art review. Excluded were also studies presenting research protocols or pilot data, reviews, and meta-analyses.
The search was conducted using the electronic databases PubMed, Web of Science, and Medline. Similar key words as suggested by Henshaw and Ferguson (2013), including “hearing loss OR hearing aid* OR hearing impair* AND auditory training OR auditory learning OR perceptual training OR perceptual learning,” were applied. Web of Science database was used to check studies citing the Henshaw and Ferguson review, and additional screening of reference lists was conducted. The search revealed 259 records after checking for duplicates, of which 53 articles were included in the full-text analysis. In total, 16 articles met all criteria and were included in this review (see Fig. 1). An overview of the 37 excluded studies can be found in the supplementary (see Table Supplemental Digital Content 2, http://links.lww.com/EANDH/A580, and reference list Supplemental Digital Context 3, http://links.lww.com/EANDH/A581).
The 16 studies considered for the present state-of-the-art review are summarized, see Table Supplemental Digital Content 1, http://links.lww.com/EANDH/A579 for the overview.
Training groups included individuals with hearing impairment above the age of 49 years. Participants were individuals with hearing impairment without any hearing aid experience (Anderson et al. 2013a,2013b; Ferguson et al. 2014; Kuchinsky et al. 2014; Karawani et al. 2015; Morais et al. 2015), individuals with hearing impairment who were fitted with hearing aids at the beginning of the study (Lavie et al. 2013; Lessa et al. 2013; Abrams et al. 2015; Rishiq et al. 2016; Rao et al. 2017; Yu et al. 2017), or experienced hearing aid users (Barcroft et al. 2016). Two studies compared novice and experienced hearing aid users (Olson et al. 2013; Saunders et al. 2016), and one included a mixed group of individuals with hearing impairment with and without hearing aids (Humes et al. 2014). Overall, the sample sizes of the different studies ranged from n = 16 to n = 279, with a median group size of n = 54 participants (SD = 60.7).
There were large variations in training stimuli, frequency and duration of training, as well as overall complexity of the training program among the 16 studies (see Table Supplemental Digital Content 1, http://links.lww.com/EANDH/A579). Auditory material included nonlinguistic sounds like pure tones or instrumental sounds as well as speech-related stimuli such as phonemes, words, and sentences. One study applied a music training protocol (Lessa et al. 2013), in which the participants trained auditory temporal processing skills. Tasks in the music training protocol included discrimination of frequency and duration of sounds, directed listening, rhythm, and auditory closure. Cognitive skills such as auditory attention and auditory working memory were trained as well.
Other studies used a single training task, which included either phoneme discrimination using phoneme continua (Ferguson et al. 2014; Yu et al. 2017) or speech perception training in noise using words and/or sentences (Humes et al. 2014; Kuchinsky et al. 2014; Abrams et al. 2015; Rishiq et al. 2016; Rao et al. 2017). Three of the studies that trained speech perception in noise focused their training on audiovisual speech comprehension (“ReadMyQuips”) (Abrams et al. 2015; Rishiq et al. 2016; Rao et al. 2017). For this training protocol, auditory speech was presented in noise in combination with visual input on a computer screen. The training of another study was based on the involvement of the participant in active conversations over a certain time (Lavie et al. 2013).
Seven studies used a more complex auditory or auditory–cognitive program including several training tasks. These protocols included commercially available programs such as LACE program (Olson et al. 2013; Karawani et al. 2015; Saunders et al. 2016), “BrainFitness” (Anderson et al. 2013a,2013b), “clEAR” (formerly “I hear what you mean”) (Barcroft et al. 2016), or other, self-developed, protocols (Morais et al. 2015). “LACE” is a training program that focuses on speech perception training in the form of speech-in-noise perception, competing speaker paradigms and compressed speech. Cognitive skills are also trained in a word memory task. “BrainFitness” includes temporal processing tasks such as discrimination of frequency-modulated sweeps and speech perception training. These tasks include discrimination of syllable pairs, or matching pairs of syllables and words, and more cognitive tasks like remembering multipart commands or details of stories, or the repetition of sequences of words or syllables. The training protocol of “clEAR” included matching audiovisual pairs of words or sentences, target-sound identification in presented words, filling in the last word of a sentence, and a discourse comprehension tasks in which participants had to answer questions about a speech passage that was presented in noise.
According to the inclusion criteria of this review, all studies compared the results of the training group to a nontraining or placebo-training group. In 13 of the 16 publications, the control groups either did not get any training intervention or an unrelated placebo-training. Among these 13 studies, six studies compared the improvement in communication skills between two groups of newly fitted hearing aid users. Both groups were fitted with hearing aids (including some information sessions on the new devices and hearing with hearing aids) in the beginning of the trial. The control group only experienced the acclimatization to the hearing aids without any further training (Lavie et al. 2013; Lessa et al. 2013; Abrams et al. 2015; Rishiq et al. 2016; Rao et al. 2017; Yu et al. 2017). Three studies applied a repeated measures design with a delayed training protocol in which the waiting group served as control group (Olson et al. 2013; Ferguson et al. 2014; Karawani et al. 2015).
Outcome Measures •
An inclusion criterion for studies in this review was that training benefits were assessed for at least one untrained, objective speech perception measure comparing pre- and post-training results. Speech perception measures were typically standardized speech perception tests assessing the recognition of words, pseudowords, or sentences in silence or in noise pre- and post-training. Additional outcome measures reported were other untrained auditory skills such as frequency or duration discrimination or gap detection (Karawani et al. 2015; Morais et al. 2015) and cognitive performance, that is, auditory attention or auditory working memory (Anderson et al. 2013a,2013b; Ferguson et al. 2014; Saunders et al. 2016; Rao et al. 2017). In three studies (Olson et al. 2013; Ferguson et al. 2014; Saunders et al. 2016), self-perceived benefit of AT was measured with well-established questionnaires (e.g., the Glasgow Hearing Aid Benefit Profile [GHABP] Gatehouse 1999) or the Speech and Spatial Qualities of Hearing Scale (SSQ, Gatehouse & Noble 2004). Neural correlates (Anderson et al. 2013a,2013b; Morais et al. 2015; Rao et al. 2017) or pupillometry (Kuchinsky et al. 2014) were included in a few studies, as well as indirect measures such as compliance of participants, or hearing aid usage.
Study Design •
All but two (Lessa et al. 2013; Kuchinsky et al. 2014) studies reported about a (partly) randomized or pseudorandomized assignment of their groups into intervention and control groups. All training protocols required regular training with µ = 18 training sessions. Only few studies applied less than 10 training sessions (Lavie et al. 2013; Lessa et al. 2013; Morais et al. 2015), whereas others applied up to 40 sessions (Anderson et al. 2013a,2013b). Training duration and frequency also varied strongly. Participants trained for 15 to 90 minutes per session on 1 to 6 days per week for about 4 to 8 weeks (see Table Supplemental Digital Content 1, http://links.lww.com/EANDH/A579, training frequency). In the study by Abrams et al. (2015), it was noted that the participants in the training group spent overall less time with training than prescribed by the study protocol.
On-task learning is defined as a measurable improvement in the trained task. Nine out of 16 studies did not report about on-task effects after AT. All seven studies that reported on-task effects observed a significant improvement in the trained tasks (Ferguson et al. 2014; Humes et al. 2014; Kuchinsky et al. 2014; Karawani et al. 2015; Barcroft et al. 2016; Saunders et al. 2016; Rao et al. 2017; Yu et al. 2017). A few studies reported on-task benefits tested with new talkers or stimuli materials but for the same task (Kuchinsky et al. 2014; Barcroft et al. 2016).
Transfer of Learning
In total, 10 out of 16 studies showed a significant improvement of the training group on the objective speech measure (Lavie et al. 2013; Lessa et al. 2013; Olson et al. 2013; Anderson et al. 2013a,2013b; Kuchinsky et al. 2014; Karawani et al. 2015; Morais et al. 2015; Rao et al. 2017; Yu et al. 2017). The remaining six studies did not reveal a significant transfer effect of AT (see Table Supplemental Digital Content 1, http://links.lww.com/EANDH/A579, and Table 1).
In the studies that used more than one speech perception outcome measure to assess training benefit, the training effect was found for all applied outcome measures, with a few exceptions. For example, Olson et al. (2013) evaluated the LACE protocol in novice and experienced hearing aid users. Pre- and post-training, speech perception skills were tested with three objective tests, i.e., QuickSIN, compressed speech perception, and synthetic sentence identification. Improvements after training were observed for the QuickSIN and for the synthetic sentence identification, whereas compressed speech perception did not improve. Similarly, Yu et al. (2017) showed an improvement for novice hearing aid users in sentence recognition after training of consonant, vowel, and sentence discrimination in noise, whereas vowel discrimination performance remained unchanged after training
Effects on Neural Correlates
Some studies assessed AT effects on complementary neural measures. For example, Anderson et al. observed improved neural representation of speech presented in noise after AT (Anderson et al. 2013a,2013b). On the other hand, differences in event-related potentials after the training could not be observed (Morais et al. 2015; Rao et al. 2017). Rao et al. (2017) reported that in novice hearing aid users P300 event-related potential components reduced during the acclimatization phase after fitting hearing aids, but no further reduction was observed after AT. However, the reduction in amplitude was correlated with a change in signal detection, and this correlation was maintained in the training group and absent in the control group after AT. Kuchinsky et al. (2014) recorded pupillometry data in their groups of individuals with hearing impairment and showed that AT resulted in faster peaking and larger pupil response in the training group for untrained word identification, which was not the case in the control group.
Effect on Cognition
Studies using additional outcome measures to assess the transfer of AT on cognition observed varying results. A few studies found beneficial effects on auditory attention tasks (Anderson et al. 2013a; Rao et al. 2017) and processing speed (Anderson et al. 2013b) after training. However, effects did not generalize to cognitive functions in all studies; improvements in working memory skills were observed only by Anderson et al. (2013b), whereas others did not observe any improvement (Ferguson et al. 2014; Morais et al. 2015; Saunders et al. 2016). However, it should be noted that in the studies showing an improvement in cognitive functions, training included cognitive aspects (e.g., Anderson et al. 2013a,2013b).
Ferguson et al. and Olson et al. measured self-perceived benefit of AT, with varying results. Olson et al. (2013) assessed changes in the International Outcome Inventory-Hearing Aid, the International Outcome Inventory-Alternative Intervention, and the SSQ after AT in experienced and novice hearing aid users. The International Outcome Inventory-Alternative Intervention showed that new hearing aid users perceived a benefit from training compared with experienced hearing aid users. Group differences on the SSQ were not statistically significant, but 63% of new hearing aid users showed an overall improvement in the SSQ. Ferguson et al. (2014) assessed AT effects on the SSQ and the GHABP in adults with mild–moderate hearing loss. The SSQ did not show any improvements post-training. The analysis of the GHABP showed a significant improvement pre- versus post-training for the Disability but not for the Handicap scale. The post hoc analysis of the Disability situations showed that the situation of group conversation significantly improved after training. The authors speculate that self-report is related to performance, as nine participants of the training group showed an improvement in both self-report and divided attention (Ferguson et al. 2014).
Long-term effects of AT were assessed in six out of 16 studies (Lavie et al. 2013; Anderson et al. 2013b; Ferguson et al. 2014; Rishiq et al. 2016; Saunders et al. 2016; Yu et al. 2017). Two studies did not observe any benefit of AT right after training; consequently, also long-term effects were not evident (Rishiq et al. 2016; Saunders et al. 2016). For the other four studies, long-term follow-ups were performed 2 to 4 weeks (Ferguson et al. 2014; Yu et al. 2017) and 2 to 6 months (Lavie et al. 2013; Anderson et al. 2013b) after the end of training. Effects of training persisted over time in three out of four studies (Anderson et al. 2013b; Ferguson et al. 2014; Yu et al. 2017).
The aim of the present state-of-the-art review was to summarize recent evidence on the benefit of rehabilitative AT for individuals with hearing impairment. Specifically, the review evaluated the transfer of learning from AT to performance on untrained speech perception tasks to assess generalization of training effects toward more realistic communication abilities. Groups that were included in this review were elderly individuals with hearing impairment without hearing aids and groups of experienced and novice users of hearing aids.
The majority of studies evaluated for this review had at least one outcome measure testing an untrained task that shows an improvement after a period of AT. This overall outcome supports the notion that AT is a beneficial intervention strategy for elderly individuals with hearing impairment. Several aspects that influence the effectiveness of AT will be discussed in the following.
The present state-of-the-art review considered exclusively control trials. In control trials, compilation of groups is usually randomized or pseudorandomized to ensure a matching in, for example, age, gender, or hearing level. In the previous review by Henshaw and Ferguson (2013), it was shown that at that time only three out of 13 studies fulfilled the quality criteria of having an appropriate control group (see Table 5 in the original publication). The authors proposed recommendations for future research, that is, to include control groups in training studies. It might be a consequence from this recommendation that the present literature shows a slight improvement in high-level evidence assessment as 16 studies were found that reported results in comparison to a control group.
Assessment of Training Effects
The comparison of training effects to a nontraining or placebo-training group is of high importance, as high level of evidence can only emerge from designs where the benefit of training can be disentangled from effects of learning occurring during everyday listening and active communication. It is possible that individuals without training can reach the same level of performance by everyday listening and learning in daily-life settings as individuals who undergo a structured training. However, the structured training might speed up the process of perceptual learning. A long-term follow-up helps to further isolate the effect of structured AT. Long-term persistence of enhanced performance after training was observed in three out of the six studies that examined long-term differences between AT and control groups, suggesting that AT can indeed lead to benefits beyond naturally occurring learning effects. A focus on the long-term effects of AT would be of great importance to further interpret what advantage auditory (-cognitive) training has for elderly individuals with hearing impairment in their daily life (Henshaw & Ferguson 2013; Lawrence et al. 2018).
In all studies, speech perception performance after training was the indicator for successful learning. If the group performance in the speech perception test did not increase significantly post-training compared with pre-training, AT was regarded ineffective (cf. 6 out of 16 studies). Such an interpretation should be done carefully. Poor test–retest reliability of speech perception measures is one factor that may lead to reduced statistical effect sizes, especially for smaller effects. Improvements in daily life situations, for example, in quality of life or self-confidence of individuals, may occur also in the absence of a significant improvement in a speech perception task. The aspect of self-perceived benefit of AT is of great importance, especially for the clinical implication. The self-perceived benefit might be one of the closest assessments of a real-world benefit that exists in audiology. For example, effects of training on quality of life and self-confidence of individuals have been shown to directly affect communication skills (Boothroyd 2010; Henshaw & Ferguson 2013). Such a subjective measure is rather difficult to validate, especially if it is contradictory to no improvement in speech perception skills measured in the laboratory. The effort spent in, for example, showing compliance to the training schedule might also influence the self-perceived benefit and may be even the auditory performance, which would then in fact be driven by motivation rather than perceptual learning. In line, Abrams et al. (2015) reported that the daily hearing aid wear time declined in the group without AT, whereas the people in the training group did not reduce their daily wear time. Despite the fact that this was only a statistical trend, AT might be a relevant factor to increase satisfaction as well as acceptance and compliance in new hearing aid users. The influence of self-perceived improvement as well as the relationship of improvement and self-engagement should be in the focus of future research.
An improvement on the trained task after a certain amount of training is robustly observed in many training studies. As not all studies reported on-task benefits, it can only be assumed that on-task effects were measured but simply not reported in these studies. However, to assess any transfer of learning, the on-task learning should be proven first as a basis for an effective training. Future studies should therefore always assess and report the on-task effects.
AT for Individuals With Hearing Impairment
Elderly individuals with hearing impairment fitted with hearing aids seem to benefit substantially from accomplishing an auditory (or auditory–cognitive) training within the first weeks of hearing aid use. This benefit is reflected in about 16% to 20% sentence recognition improvement (Megale et al. 2010; Olson et al. 2013). The effect seems to be specifically due to training as participants without training did not show a similar improvement in speech perception despite the before mentioned expected everyday learning (Rao et al. 2017). Further supporting evidence is that experienced hearing aid users showed a smaller training effect compared with novice hearing aid users (Saunders et al. 2016; Smith et al. 2016). The better baseline of experienced hearing aid users compared with inexperienced users is presumably a result from everyday learning over time. Despite being smaller, training effects can still be observed in this experienced group indicating that training can be an additional booster to everyday learning even after getting used to the new sensory input from hearing aids. Based on these findings, AT could be used to support the patients throughout the hearing aid acclimatization phase by actively requesting engagement (e.g., training) of the patient in the whole process (Martin 2007; Olson et al. 2013). The overall awareness of hearing and “relearning” to hear might help to set realistic expectations of the hearing aid users. However, before a standardized implementation of AT in the hearing aid fitting process can happen, a deeper understanding of the relationship between AT and acceptance of hearing aids is of great interest and should be investigated in future studies.
Another important aspect is to encourage hearing aid users or elderly individuals with hearing loss to commit to intense training programs. So far, most of the results provided by the literature are based on motivated people who accept doing the training over several weeks. In general, training must be accepted with the focus on the effectiveness of AT to enhance cognitive and social functions in the elderly (Burk & Humes 2008; Humes et al. 2009b). Easy-to-use and home-based training might be crucial to implement structured training in a daily-life setting for elderly individuals. Moreover, access to training on mobile devices and gamification of training paradigms (including, for example, rewards for achievements) might help to keep the motivation of the trainees high (Henshaw et al. 2015; Groznik & Sadikov 2019). Conversely, self-managed training eliminates the social component, which is a very important factor. Other setups of training, for example, regular meetings of individuals with hearing impairment, are not included in this review. The social aspect may help to boost the self-confidence of individuals with hearing impairment and enhance social engagement. Therefore, while the social aspect may be less relevant for perceptual skills, it may enhance self-perceived performance, with direct consequences on the communication behavior. The ideal AT program might therefore be a combination of a social component and self-administered perceptual training.
Effect of Training Protocol
A few studies investigated the effect of training protocol differences with the same amount of training spread over a longer time period or more condensed in a shorter amount of time. Differences in design did not influence training benefit (Humes et al. 2014; Tye-Murray et al. 2017). Abrams et al. (2015) investigated whether the number of hours spent on AT has an influence on the outcome measure. Despite the fact that the overall difference on speech-in-noise performance was not significant between the training and the control group, the number of hours spent with AT showed a positive correlation with an improvement in speech-in-noise understanding in the training group. Another study showed that the largest improvement in speech perception occurred after between five and 10 training sessions, each 30 minutes per day for 5 days a week (Olson et al. 2013). For the implementation of AT in hearing aid rehabilitation, it seems necessary to motivate the participants to take part in consistent training several days per week for a longer time period to achieve success. Similar to perceptual training, AT produces plastic changes in the brain to enhance functionality; it seems very plausible that longer and intensive training is necessary.
Half of the studies that applied AT paradigms using speech material (often using phonemes, consonants, and vowels but also words and sentences) showed improvement in speech perception measured with untrained, standardized tests. The training programs LACE, BrainFitness, and clEAR are training programs with various auditory tasks (using ecologically relevant speech stimuli) that also include cognitive (e.g., auditory working memory or auditory attention) or audiovisual tasks. Most studies applying any of these three training programs found benefits for untrained speech perception tasks (Olson et al. 2013; Anderson et al. 2013a,2013b; Karawani et al. 2015; Morais et al. 2015). Such varied paradigms seem to be the most efficient training programs to improve speech perception (in noise) with additional benefits for auditory cognitive capacities. This supports the conclusion of a recent meta-analysis and review looking at the effect of auditory or cognitive training to improve cognitive skills in elderly individuals with hearing impairment (Lawrence et al. 2018). However, some caution is necessary, given that some studies using a similarly intense training protocol did not observe any beneficial effects of training on speech perception or cognition (Barcroft et al. 2016; Saunders et al. 2016). Reasons for these differences in outcome may be various, for example, the training intensity, which differed between studies using the same training protocol (i.e., LACE: 10 sessions over 2 weeks in Saunders et al. and 20 sessions over 4 weeks in Olson et al.).
Compliance to and Acceptance of AT
Recently, studies have focused on the compliance to AT, validating that elderly participants are able and inclined to use computer-based auditory rehabilitation programs (Henshaw et al. 2015; Ferguson et al. 2016). A post-training feedback questionnaire showed that the majority of participants had extrinsic motivation due to their hearing problems to take part in the training study (“I did the training because it might make my hearing better”). The questionnaire also showed that intrinsic motivation was high enough to sustain through the program's entirety (“I enjoyed training with the program”) (Henshaw et al. 2015). Intrinsic motivation can easily be diminished by factors such as technical problems, unsatisfactory feedback in the training software, or boring tasks.
In this review, studies that reported on compliance found high rates, with 70% to 80% of participants completing the entire training (Chisolm et al. 2013; Henshaw & Ferguson 2013; Olson et al. 2013; Karawani et al. 2015; Saunders et al. 2016). A recent study specifically investigated the influence of compliance on the transfer to untrained tasks (Chisolm et al. 2013). Compliance in the study by Chisolm et al. (2013) was high with 84% of participants completing all 20 sessions, 6% completing 10 to 19 sessions, and 10% completing less than 10 sessions. Post hoc analyses of training benefit for compliant (n = 42) and noncompliant (n = 8) groups showed that the compliant group achieved an improvement in speech perception performance, whereas the noncompliant group did not show a significant change (Chisolm et al. 2013). However, the difference in sample size as well as other unknown factors and reasons for noncompliance is a concern for this analysis. Also Abrams et al. (2015) observed that there was a positive relationship between the number of hours spent on training and the improvement in words-in-noise perception.
Last but not least, audiologists must also take an active role in commitment to training. It is estimated that currently less than 10% of audiologists offer AT to patients with hearing impairment (Sweetow& Sabes, 2006,2010; Li-Korotky 2012). To use AT as a successful tool, individual training programs need to be incorporated in the early stages of auditory rehabilitation suggested by the hearing care professionals (Sweetow & Sabes 2010; Li-Korotky 2012). Assessment of costs and benefit, for patients and professionals, is needed to successfully implement AT in the routine of auditory rehabilitation of individuals with hearing impairment.
Based on the recent evidence evaluated in this state-of-the-art review, intensive auditory (-cognitive) training protocols seem to be a valid tool to improve auditory communication skills, especially, if they include a combination of auditory and cognitive tasks. Individuals with hearing impairment seem to benefit the most using a combination of sensory rehabilitation with hearing aids and AT. Accordingly, AT can be used as a tool to support auditory rehabilitation with the outcome of enhanced self-perceived benefit as well as enhanced auditory skills. Given the limited availability of data on persistence of training effects over longer periods of time after training, it remains uncertain, whether training needs to be continued consistently or in repeated intervals to achieve long-term benefits.
We thank Jena Anne Schnittker for proof-reading the manuscript.
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