Smartphone Apps in the Context of Tinnitus: Systematic Review [original]

sensors

Review

Smartphone Apps in the Context of Tinnitus:

Systematic Review

Muntazir Mehdi 1,*, Constanze Riha 2, Patrick Neff 3,4 , Albi Dode 5, Rüdiger Pryss 5,

Winfried Schlee 3, Manfred Reichert 5and Franz J. Hauck 1,*

1Institute of Distributed Systems, Ulm University, 89081 Ulm, Germany

2Department of Psychology, University of Zürich, Box 1, CH-8050 Zürich, Switzerland;

[email protected]

3Clinic and Polyclinic for Psychiatry and Psychotherapy, 93053 Regensburg, Germany;

[email protected] (P.N.); winfried.schlee@tinnitusresearch.org (W.S.)

4URPP Dynamics of Healthy Aging, University of Zürich, Box 2, CH-8050 Zürich, Switzerland

5Institute of Databases and Information Systems, Ulm University, 89081 Ulm, Germany;

[email protected] (A.D.); manfr[email protected] (M.R.); ruediger[email protected] (R.P.)

*Correspondence: muntazir[email protected] (M.M.); [email protected] (F.J.H.)

Received: 7 February 2020; Accepted: 17 March 2020; Published: 19 March 2020

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Abstract:

Smartphones containing sophisticated high-end hardware and offering high computational

capabilities at extremely manageable costs have become mainstream and an integral part of users’

lives. Widespread adoption of smartphone devices has encouraged the development of many

smartphone applications, resulting in a well-established ecosystem, which is easily discoverable and

accessible via respective marketplaces of differing mobile platforms. These smartphone applications

are no longer exclusively limited to entertainment purposes but are increasingly established in the

scientific and medical field. In the context of tinnitus, the ringing in the ear, these smartphone

apps range from relief, management, self-help, all the way to interfacing external sensors to better

understand the phenomenon. In this paper, we aim to bring forth the smartphone applications in

and around tinnitus. Based on the PRISMA guidelines, we systematically analyze and investigate the

current state of smartphone apps, that are directly applied in the context of tinnitus. In particular,

we explore Google Scholar, CiteSeerX, Microsoft Academics, Semantic Scholar for the identification

of scientific contributions. Additionally, we search and explore Google’s Play and Apple’s App Stores

to identify relevant smartphone apps and their respective properties. This review work gives (1) an

up-to-date overview of existing apps, and (2) lists and discusses scientific literature pertaining to the

smartphone apps used within the context of tinnitus.

Keywords: mobile health; smartphone apps; tinnitus research; biomedical and health informatics

1. Introduction

Tinnitus is a complex and heterogeneous disorder associated with causing the perception of a

continuous clicking, ringing, roaring, or buzzing sound (noise) in the ears in absence of any external

sound source. Approximately 15% of the world’s population suffers from tinnitus, wherein 2% of

these experience a substantial decrease in quality of life due to the phantom percept [

]. Many

factors associated with causing this phantom sound are still unknown, yet, it is often associated with

an underlying damage in the ear, such as the loss of cochlear hair cells. The loss of the hair cells

can have different origins: a common risk factor is an acoustic trauma (exposure to loud sounds),

the same applies to ototoxic drugs. However, tinnitus can also develop as a symptom of a cochlear

affecting disease, such as Ménière’s disease (MD), or in the course of aging and age-related hearing loss

Sensors 2020,20, 1725; doi:10.3390/s20061725 www.mdpi.com/journal/sensors

Sensors 2020,20, 1725 2 of 21

(presbycusis) [

]. Age-related physiologic changes, for example, degeneration of sensory receptor

cells, are one common cause of disorders of the sensory systems, like the auditory system [

]. Further

age-related changes have been identified in auditory processing in the brain and may be related to

the generation of dementia [5,6]. Besides the increased risk of tinnitus with higher age, elder persons

have also been shown to experience more tinnitus-related distress which is theorized to be related to

decreased compensatory brain plasticity [

]. In a steadily aging society, presbycusis and tinnitus thus

become more prevalent with consequences beyond auditory sensory handicaps.

Presently, tinnitus is considered as a condition that involves changes at different levels of the

auditory pathway, the auditory cortex as well as non-auditory areas like the limbic system. These

changes may additionally be influenced by psycho-social stress (for example, negative thoughts,

the argument at home, increased workload, etc.), affecting the emotional status and the auditory

system [

]. Consequently, variations in tinnitus loudness and tinnitus-related distress, as well as the

individual perception of tinnitus has been often reported by tinnitus patients [

]. Additionally, tinnitus

variations can be directly or indirectly affected by changes in the atmospheric surrounding [

] and

environmental conditions of the patient [

]. Individual case studies on weather conditions and their

impact on fluctuations in tinnitus show limited but some evidence of a connection [

]. In patients

suffering from MD [

], which commonly occurs with hyperacusis [

], a weather change usually

contributes to tinnitus increase [

]. Abrupt change in barometric pressure (particularly reduced

pressure) may cause or increase tinnitus symptoms because it affects the eardrum, the round window,

and the cochlear fluids. Increased wind speed or humidity also worsen the tinnitus symptoms due to

influences of high sensitivity on the ears [12]. A similar relationship applies to seasonal change [19].

Smartphone-based Ecological Momentary Assessments (EMA) methods can be utilized to capture

the variations in tinnitus perception and link them to current surrounding or environmental conditions

of the patient [

]. Furthermore, the tinnitus variations related to stress can be coped with using

smartphone-based Cognitive Behavioural Therapy (CBT) or self-help apps, and individual perception

of tinnitus can be managed using smartphone-based tinnitus relief apps. Despite smartphones,

smartphone apps, and auxiliary health devices, for instance, heart meters, activity trackers, and

smart wristbands, have become popular in assisting patients in managing and controlling their health

problems [

], further research to determine the effectiveness of these applications and devices

in different domains of healthcare is still required [

]. Nonetheless, smartphones are interesting

in particular as most of today’s smartphones provide high computational power, a long-lasting

battery life, and incorporate a set of sophisticated built-in sensors that are capable of accurately

monitoring environmental surroundings and can be programmed and managed by apps. Additionally,

smartphones provide an application ecosystem, extendable to program and include new apps targeting

different health problems at almost negligible costs. New smartphone apps can be designed or existing

apps can be tailored to assist in managing or mitigating the symptoms of different health problems [

For instance, mobile crowdsensing and smartphone-app solutions can be applied to monitor the

ecological or environmental surroundings of patients using the built-in sensors [

]. Similarly,

for tinnitus, these smartphone-app–based solutions also apply. However, due to the fast-growing

development and the continuous publishing and inclusion of new apps in the app market places, the

current state of smartphone apps within the context of tinnitus is mostly unbeknownst to patients and

clinicians alike.

In this paper, based on the PRISMA guidelines [

], we explore online scientific literature sources

namely: Google Scholar, CiteSeerX, Microsoft Academics, and Semantic Scholar as well as app stores,

namely: Google’s Play Store and Apple’s App Store to list and identify tinnitus-related smartphone

apps. The idea of this paper is to list and index smartphone-based solutions for assisting patients

suffering from tinnitus, to foster a better understanding, management and treatment (by the provision

of therapeutic solutions), as well as monitoring the severity of their tinnitus. Likewise, we report

on apps that succor tinnitus patients in testing for hearing impairment (usually accompanied by

tinnitus [29]), and, if possible, protect and train the remaining hearing abilities.

Sensors 2020,20, 1725 3 of 21

A review by Sereda et al. [

] lists tinnitus management apps based on patient opinions, gathered

via a web-based survey. Moreover, the apps identified through a web-based patient survey are further

evaluated based on the Mobile Application Ratings Scale (MARS) [

]. The added value from our

review is primarily the exploration of the smartphone app markets to reveal relevant apps, as opposed

to using a survey. The review by Kalle et al. [

] discusses internet- or smartphone-delivered CBT,

with particular focus on self-help for tinnitus. The authors demonstrate the role of several approaches

in advancing tinnitus clinical practice, but have focused less on current and available apps for patients.

The review by Lui et al. [

] addresses efficacy or effectiveness of mental-health-app–based therapeutic

solutions, but not with a particular focus on tinnitus. However, they do consider apps based on CBT,

one of the most common therapies in the tinnitus domain. In our review, we do not limit the scope

to CBT, self-help, or mindfulness apps, rather we expand further to address apps that also fall into

the non-therapeutic category. In another article [

], the authors have outlined hearing healthcare

apps from prominent smartphone platforms. However, the list of apps is limited and most apps have

been outdated. Similarly, Bright and Pallawela [

] discuss smartphone apps for hearing assessments

including comparison and validation of apps. In comparison, the scope of our proposed work is

not limited to hearing assessments, but further includes additional apps for hearing healthcare, for

instance, hearing protection and enhancement apps.

In summary, unlike the aforementioned studies and reviews, the objective of the presented

review is to identify and report on smartphone-based solutions (apps specifically), within the context

of tinnitus, that are, in turn, widely and easily available on mainstream app stores. Additionally,

a further objective is to report on the current state of smartphone-based app solutions presented in

the literature, be that either in the form of discussing the underlying technology or technique used

for the development of the smartphone app, or the effectiveness of the smartphone apps for tinnitus

patients. The overall process of identification of smartphone apps on scientific literature sources as

well as on app store markets is detailed in Section 2. The identified results are reported and discussed

in Section 3. Before concluding the article, the limitations and potential directions of proposed reviews

are reported in Section 4.

2. Review Design

2.1. Finding Relevant Literature

The workflow diagram for the systematic identification of scientific literature is illustrated in

Figure 1. The sources (Google Scholar, CiteSeerX, Semantic Scholar, and Microsoft Academic) were

queried to find relevant literature from 2017 and onwards. The keywords used to perform searches are

(tinnitus OR hearing) AND (smartphone OR mobile) AND (Apps OR systems). Two separate cycles

of searches were performed on different dates: (1) 15

May

2019, and (2) 15

November

2019. Finally,

the results were fused together, duplicates removed and prepared for further screening.

A total of

214 records were considered for screening in the identification phase (Figure 1).

In a further step, a screening was performed on the titles and abstracts of these selected records for

eligibility, which resulted in the feasibility of

76 records for further evaluation. The full texts of

the selected 76 records were then assessed for further suitability, resulting in a rejection of further 25

records due to several reasons: 6 out of the 25 records were not subjected to a peer-review process.

11 records did not perform any qualitative or quantitative analysis of the respective app or did not

reference any app. 8 records did not show any meaningful overlap with the content, aim and scope of

this review. Finally, the review selection process resulted in the inclusion of 51 records, whereas 13

articles were additionally added through a review of references. Finally, the total number of included

records was, therefore,

64. The identified literature has been subsequently categorized with the

help of tinnitus experts into six topics: 1) tinnitus relief (

14), 2) CBT (

10), 3) hearing protection

(

08), 4) hearing testing (

11), 5) hearing enhancement (

10), and 6) smartphone-based

mobile EEG systems (n=11).

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From: Moher D, Liberati A, Tetzlaff J, Altman DG, The PRISMA Group (2009). Preferred Reporting Items for Systematic Reviews and Meta-

Analyses: The PRISMA Statement. PLoS Med 6(7): e1000097. doi:10.1371/journal.pmed1000097

For more information, visit www.prisma-statement.org.

PRISMA 2009 Flow Diagram

Records identified through database searching

Dates: January 2017- November 2019

(n = 3550)

Screening

Included

Eligibility

Identification

Records after duplicates removed

(n = 214)

Records screened

(n = 214)

Records excluded

(n = 138)

Title/Abstract Screening

Full-text articles assessed

for eligibility

(n = 76)

Full-text articles excluded,

with reasons

(n = 25)

Non peer-reviewed article

(n=6)

No qualitative or

quantitative analysis of any

app or reference to any app

(n=11)

No reference to domain of

study of this review (n=8)

Studies included in

synthesis

(n = 51)

Studies included in

narrative synthesis

(n = 64)

Articles identified through

references review

(n = 13)

Google Scholar

(n = 1119)

CiteSeerX

(n = 1924)

Semantic Scholar

(n = 255)

Microsoft Academic

(n = 252)

Categories

Figure 2. Prisma workflow for systematic review—apps.

2.3. Rationale Behind App Categorization

In addition to the apps related to tinnitus relief, we report on apps that provide CBT or self-help,

helpful for hearing loss as it is one of the major causal risk factors [

], and smartphone-based

mobile EEG systems. The rationale behind the categorization of apps into six topics identified through

literature screening and surveying the apps stores are further detailed below:

Tinnitus Relief

Different treatment modalities for the management of tinnitus symptoms exist, for

instance, Tinnitus Retaining Therapy (TRT), Tinnitus Masking (TM), conventional drug delivery,

and even brain stimulation—among them, TRT, TM using sound generators, and CBT as

counseling are standard treatment procedures [

]. Most of the tinnitus relief apps that are

generally published on app markets offer tinnitus masking, or sound therapies using different

sound techniques like acoustic neuromodulation, notched sound, or amplitude modulation.

Smartphones are capable of delivering acoustic and sound therapy reliably and accurately [39].

CBT

Although, the acoustic characteristics of tinnitus, particularly the subjective loudness of tinnitus

is minimally affected by CBT [

], CBT has been pivotal for the treatment of tinnitus [

]. Since

CBT and self-help therapies have been useful in dealing with stress and anxiety associated with

tinnitus [42], we deem it important to be included in this review.

Hearing protection

Tinnitus is reported to be accompanied by hearing loss in more than 80% of

cases [

]. Augmentation of tinnitus symptoms with increased noise exposures [

], and hearing

loss being prevalent causal risk factor for tinnitus [

], it can be argued that hearing protection

can lead to reduced odds for developing tinnitus, as well as support tinnitus patients in managing

their symptoms.

Hearing testing

Since hearing loss is a commonly occurring phenomenon with tinnitus, we argue

that apps for hearing testing are certainly linked to processes of tinnitus matching (for example,

sensation levels for staircase procedures). Therefore, smartphone-based tinnitus matching may

be a relevant feature for current or future sound therapies. Furthermore, in patients where the

tinnitus is caused by hearing damage, using hearing aids (or even cochlear implants) can help to

reduce tinnitus symptoms [

]. Therefore, we believe that it makes sense for the tinnitus patients

to test their hearing and thus hearing testing apps are relevant for this review.

Hearing enhancement

Tinnitus and hearing loss has been reported to directly influence the quality of

life of patients [

]. Apps for hearing enhancement could be useful to counteract tinnitus-related

Sensors 2020,20, 1725 6 of 21

impairments of hearing functions in daily life like speech in noisy environments or cocktail-party

situations, and directional hearing. Therefore, we consider our addition of hearing enhancement

as rather straight forward.

Smartphone-based EEG

Despite the fact that tinnitus is traditionally considered only a problem of the

inner ear, research using brain imaging has shown that the complexity of tinnitus goes beyond the

auditory cortex into non-auditory brain areas [

]. Additionally, EEG allows the investigation

of resting-state activity of the brain [

], and is widespread in tinnitus research [

–

]. With the

growing interest in the development and significant technological advancements in mobile-based

EEG systems and due to the fact of recent developments, it is possible to record EEG outside

of a laboratory setting. Further, EEG is one approach of few to record the changes in brain

activity, which corresponds to the perception of tinnitus [

]. That is why we considered

smartphone-based electroencephalography (EEG) to be pertinent and included it in this review.

3. Results and Discussion

3.1. Tinnitus Relief Using Smartphones

A significant portion of scientific literature within tinnitus research reports on different

applications of smartphone apps and mobile crowdsensing, ranging from data collection to mitigating

tinnitus symptoms via therapeutic interventions and supporting clinicians in better understanding the

tinnitus. These applications are specifically designed to assist patients, clinicians, and researchers alike.

From the perspective of patients, these apps aim to assist patients in masking, controlling,

mitigating, or managing tinnitus symptoms by means of providing smartphone-delivered CBT, tinnitus

or sound therapy, or keeping track of individual tinnitus perception using standard questionnaires.

For instance, the smartphone app TrackYourTinnitus (TYT) [

] systematically records fluctuations

of tinnitus symptoms over time from patients using Mini-Tinnitus Questionnaire (Mini-TQ) [

]

and Visual Analogue Scale (VAS) [

]. Both Mini-TQ and VAS are employed by TYT app to

acquire tinnitus-related data such as tinnitus presence, stress, loudness, and tinnitus-related distress.

The aggregated data from the app provides information about a patient’s tinnitus variability over time,

thus, enabling patients to easily identify critical circumstances causing fluctuations in their individual

tinnitus perception [

]. This helps patients to not only have necessary knowledge and information

regarding their tinnitus but also assists them to demystify the tinnitus symptoms and establish control

over tinnitus. Similarly, Ref. [

] delve into the development of an app, based on the progressive

tinnitus management to support patients in learning and using coping skills for tinnitus management.

Ref. [

], in turn, outlines a self-management tinnitus app that combines audiometric examinations

and administration of questionnaires, namely the Pittsburgh Sleep Quality Index, PSQI, [

]; Khalfa

Hyperacusis Questionnaire [

]; Tinnitus Handicap Inventory (THI) [

]. The authors employ and

present an external device for audiometry testing and argue that the app supports patients with their

diagnostic procedures.

From the perspective of clinicians and researchers, these apps enable and support a better

understanding of different aspects of tinnitus. Among many, some of the most important ones

are to better understand and identify tinnitus severity and tinnitus behavior in different patients

and to better understand the tinnitus heterogeneity in general. For instance, the data collected from

the TrackYourTinnitus app can be used to establish a connection between tinnitus and daily routine

or activities [

]. Additionally, the same data can be analyzed to shape recruiting strategies for

larger tinnitus-related studies [

], and to better understand tinnitus variability and tinnitus–stress

associations [60]. Similarly, the similarities and differences in ecological momentary assessment data,

collected from the TrackYourTinnitus app after a long time can also help physicians to understand the

evolution of tinnitus patients [61].

In terms of tinnitus-related therapies to control tinnitus symptoms, Ref. [

] highlight the use

of sound-related therapy. Ref. [

] aims to assess and review smartphone-app–supported therapies

Sensors 2020,20, 1725 7 of 21

for tinnitus, which is argued to be useful, additionally to multimodal tinnitus therapies. In another

study, Ref. [

] employ the use of a smartphone app to deliver notched music to tinnitus patients.

It is argued in the study that the overall THI scores (emotional score of THI in particular) of tinnitus

patients improved.

A comprehensive list of apps that assist patients in providing tinnitus-related relief is shown in

Table 1, with their respective properties. Among the app properties, we identify that the users-property

will provide the readers with coverage of the apps’ usage. Please note that in the case of the iOS

platform, the number of users is not publicly provided by the app store. Rating will highlight the

impact of the app according to the app store’s rating system, update gives the last seen update on the

corresponding store. Pricing will give insights into the economical aspects of apps. The app price is

given in Euros, whereas for free apps, further categories exist: Free (I) corresponds to apps that are

available free with purchases inside the app (in-app purchases), and Free (A) corresponds to apps that

are supported by advertisements (ad supported). Please note that free apps can also come with both

combined, denoted as Free (I,A). The platform property is necessary as it explores the platform-specific

user base and their behavior towards the app. For instance, a platform-specific data-analysis-based

comparison of TrackYourTinnitus is given in [

], in which the authors aim to highlight the differences

between iOS and Android users to better understand their use of mobile apps within tinnitus context.

The difference in platform-specific user behavior to an app is also evident in Table 1when comparing

the ratings of TrackYourTinnitus app.

Table 1.

Apps providing tinnitus-related relief (Free = royalty free, Free(I) = in-app purchases, Free(A)

= ad-supported, Free(I,A) = both) *Apps reported in literature.

App Name Description Platform Users Rating Update Pricing

H& T Sound Therapy Noise Player (pink noise, white noise or brown noise) for masking tinnitus Android 10K+4.3/5.0 Oct-19 Free

Kalmeda mynoise* Offers medically-based, individual tinnitus therapy Android 1000+3.0/5.0 Jul-19 Free(I)

iOS - 3.6/5.0 Jul-19 Free(I)

myNoise* Controlling tinnitus via combination of different sounds and noises Android 100K+4.4/5.0 Mar-18 Free(I)

iOS - 4.6/5.0 Apr-19 Free(I)

Oticon Tinnitus Sound* Offers different sound types to control tinnitus Android 100K+2.0/5.0 Feb-19 Free

iOS - 2.9/5.0 Feb-19 Free

Relax Melodies* Sleep assisting app that combines sounds and melodies Android 10M+4.6/5.0 May-19 Free(I, A)

iOS - 4.8/5.0 May-19 Free(I)

Relax Noise 3* Masking tinnitus by using red, white, or pink noise Android 100K+4.2/5.0 Mar-15 Free

SimplyNoise* Controlling and managing stress and tinnitus using white, and brown noises Android 50K+3.7/5.0 Jun-12 Free

iOS - 4.4/5.0 May-18 Free(I)

Starkey Relax* Tinnitus masking, self-management, and education app Android 10K+4.3/5.0 Oct-17 Free

iOS - 3.9/5.0 Oct-17 Free

StopTinnitus* Masking tinnitus using customised tones Android 100+2.7/5.0 Jan-15 7.95e

iOS - 1.3/5.0 Jan-15 8.03e

Tinnitracks* Controlling and managing tinnitus by filtering out music for sound therapy Android 10K+3.8/5.0 Apr-19 Free(I)

iOS - 3.6/5.0 Feb-19 Free(I)

Tinnitus Balance App* Controlling annoying tinnitus using customised sounds or music Android 50K+3.7/5.0 Mar-16 Free

iOS - 2.3/5.0 Mar-19 Free

Tinnitus Help* Tinnitus masking using natural sounds or music Android 500+3.0/5.0 Nov-15 9.90e

iOS - 4.4/5.0 Jan-19 17.99e

Tinnitus Notch Provided custom tailored notch therapy for tinnitus relief Android 1000+2.7/5.0 Sep-16 Free(I)

Tinnitus Peace Offers melodies to match the frequency of tinnitus to reduce its effects Android 5K+3.8/5.0 Nov-15 Free

TinnitusPlay Tinnitus masking using different sound techniques iOS - 4.2/5.0 Dec-19 Free

Tinnitus Relief* Controlling tinnitus using information on different relaxation exercises Android 1000+4.4/5.0 Dec-13 2.99e

Tinnitus Sound Therapy Sound/Acoustic therapy for masking tinnitus Android 10K+3.9/5.0 Jun-19 Free

Tinnitus Therapy (Lite)* Avoiding tinnitus with sound masking and therapy Android 500+3.6/5.0 Feb-19 6.49e

iOS - 5.0/5.0 Mar-19 5.36e

Tonal Tinnitus Therapy* Helps to mitigate symptoms of tonal tinnitus based on acoustic neuromodulation Android 10K+4.0/5.0 Jul-18 Free(I)

Track Your Tinnitus* Managing tinnitus by tracking tinnitus patterns in daily activity Android 1000+2.1/5.0 Oct-18 Free

iOS - 5.0/5.0 Jun-17 Free

Whist* Controlling tinnitus using sounds with adjusted volume, pitch etc. Android 1000+4.2/5.0 Mar-17 2.18e

iOS - 3.7/5.0 Jan-19 1.78e

White Noise (Lite)* Masking and Controlling tinnitus using environmental sounds Android 5K+4.6/5.0 Sep-18 3.19e

iOS - 4.8/5.0 Apr-19 2.67e

Widex Zen* Avoiding tinnitus using relaxing zen sounds, and exercises to manage tinnitus Android 10K+3.8/5.0 May-17 Free

iOS - 5.0/5.0 Nov-17 Free

Sensors 2020,20, 1725 8 of 21

Further, note two important aspects for the app list shown in Table 1: the list refers to the selected

search criteria for the PRISMA guidelines, it neither claims to be complete nor can it reveal which apps

are more evidence-based as others. Although new rating systems like the Mobile App Rating Scale

(MARS) aim to establish standards in this context, their widespread use is still not given. Therefore,

systematic reviews like presented in the work at hand are currently a key factor for beneficial insights

on mobile health apps.

3.2. Smartphone-Based CBT

In addition to sound-related therapies, Cognitive Behavioural Therapy (CBT) has been pivotal for

the treatment of tinnitus [

]. Although it is argued that CBT has no effect on the acoustic characteristics

of tinnitus, such as subjective loudness of tinnitus [

]. However, it has proven to be effective in

improving the overall quality of life of tinnitus patients and reducing symptoms of tinnitus-related

psychological comorbidities, such as depression and anxiety [

]. Besides CBT being administered

face to face with a CBT clinician, it can also be administered via the internet in the form of self-help

treatment for tinnitus [

]. Evidence from the literature suggests that internet-delivered self-help

tinnitus treatment shows positive results and is an effective treatment modality [

]. Consequently,

the smartphone app markets have a variety of apps that are specifically designed for CBT for tinnitus,

such as (Beltone Tinnitus Calmer, Diapason for Tinnitus, ResoundRelief). Moreover, general CBT

self-help apps can be adapted to accommodate tinnitus-related relief, for instance, to manage and

control depression and anxiety, two of the most common and prevalent comorbidities accompanied by

tinnitus [70,71].

Our literature search did not yield any specific clinical validation studies of CBT apps directly

applied to tinnitus. However, in one study given in [

], the effectiveness of CBT in tinnitus has been

discussed and has shown positive results. The participants of the study reported reduced TFI scores

after receiving mindfulness-based CBT therapy. The study further discusses the beneficial effects of

mindfulness-based CBT in relation to distress associated with tinnitus. Although the study does not

show the usage of any specific app, mindfulness-based CBT is delivered by most of the apps listed in

Table 2.

Apps providing CBT (Free = royalty free, Free(I) = in-app purchases, Free(A) = ad-supported,

Free(I,A) = both). *Apps reported in literature.

App Name Description Platform Users Rating Update Pricing

Beltone Tinnitus Calmer* Combination of relaxation exercise and sound therapy to avoid tinnitus Android 1000+4.7/5.0 Sep-19 Free(I)

iOS - 5.0/5.0 Sep-19 Free(I)

CBT Companion Employs visual tools to learn and practice CBT techniques Android 50K+4.6/5.0 Feb-19 Free(I)

iOS - 4.7/5.0 Feb-19 Free

Diapason for tinnitus* Game-based digital therapeutic providing app for tinnitus relief Android 5K+3.1/5.0 May-19 Free(I)

iOS - - May-19 Free(I)

MindShift CBT* CBT tools to manage and control anxiety Android 100K+3.9/5.0 Oct-19 Free

iOS - 4.2/5.0 Oct-19 Free

Moodfit—Stress and Anxiety Stress and Anxiety management and tracking, and offers CBT exercises Android 5K+4.4/5.0 Aug-19 Free

Quirk CBT Self-help CBT companion based on ‘three column technique’ Android 10K+3.6/5.0 Jul-19 Free(I)

iOS - 4.7/5.0 Sep-19 Free(I)

ReSound Relief* Avoiding tinnitus using combination of sound therapy and relaxation exercise Android 100K+4.5/5.0 Feb-19 Free(I)

iOS - 4.7/5.0 Jan-19 Free(I)

Sanvello—Stress and Anxiety Help Audio and Video CBT exercises, Anxiety tracking and management Android 1M+4.6/5.0 Feb-19 Free(I)

iOS - 4.8/5.0 Nov-19 Free(I)

Stress and Anxiety Companion CBT based visual exercises to manage stress and anxiety Android 10K+4.2/5.0 Jul-19 Free(I)

iOS - 4.6/5.0 Jun-19 Free(I)

What’s Up? A Mental Health App Offers CBT and ACT methods to manage stress, anxiety as well as depression Android 50K+4.4/5.0 Jun-19 Free(I)

iOS - 4.6/5.0 Dec-16 Free(I)

Woebot - Your Self-Care Expert* A chatbot for guided CBT to manage stress and anxiety Android 100K+4.8/5.0 Nov-19 Free

iOS - 4.7/5.0 Nov-19 Free

Wysa: Mental Health Therapy* A chatbot offering CBT and DBT techniques Android 1M+4.7/5.0 Nov-19 Free(I)

iOS - 4.7/5.0 Dec-19 Free(I)

Youper - Emotional Health* A chatbot based on CBT and ACT techniques, monitoring and tracking mood changes Android 1M+4.7/5.0 Dec-19 Free(I)

iOS - 4.9/5.0 Dec-19 Free(I)

Sensors 2020,20, 1725 9 of 21

3.3. Smartphone-Based Hearing Protection

In addition to apps that support patients to manage tinnitus, the embedded microphone of a

smartphone can be used as a valid device to detect sound exposures. Herein, many smartphone

developers have contributed to the app market; i.e., with apps ranging from ones that record, visualize,

and report sound exposures to ones that help to find a quiet place. We have identified such apps and

summarized them in Table 3. For this review, we do not list apps that are solely used for the purpose

of performing sound recordings, but the focus is to have additional functionality to monitoring sound

levels. For instance, an app that records sound levels and propagates the recordings to a database,

resulting in a crowdsourcing-based noise level detection in different places or an app that detects

sound exposure and notifies the user of dangerous sound levels.

Table 3.

Apps for hearing protection (Free = royalty free, Free(I) = in-app purchases, Free(A) =

ad-supported, Free(I,A) = both). *Apps reported in literature.

App Name Description Platform Users Rating Update Pricing

Decibel X* iOS equivalent of SPL Meter and Sound Meter iOS - 4.6/5.0 Jan-19 Free(I)

dbTrack Uses earphones to measure sound exposure inside the ear canal Android 10+ - May-19 Free

Hearangel Monitors music levels, notifies extreme and dangerous sound levels Android 1000+5.0/5.0 Sep-18 Free

iHEARu Here* Crowdsourcing tool to report noise levels and find low sound exposure places Android 10000+3.1/5.0 Aug-18 Free

iOS - - Sep-18 Free

NIOSH Sound Level Meter* Notifies user of current sound environment iOS - 4.7/5.0 May-19 Free

Noise Control Measures surrounding sounds, allows recording and playback Android - - Sep-12 Free

iOS - - May-15 Free

NoiseCapture* Evaluates noise environment and reports exposure Android 100K+4.4/5.0 Mar-19 Free

NoiSee* Offers ANSI- or IEC-compliant sound level monitoring iOS - 4.6/5.0 Jan-19 0.89e(I)

NoiseScore* Documents and visualizes environmental soundscape of users Android 100+4.5/5.0 Apr-18 Free

iOS - 4.5/5.0 Apr-18 Free

Soundcheck* Identifies overexposing sounds and recommends hearing protection Android 10K+3.5/5.0 Jun-15 Free

iOS - 3.1/5.0 Jul-19 Free

Sound Meter* Measures loudness of the environment, reference sound comparison Android 10M+4.6/5.0 Apr-19 Free(A)

Sound Meter - SPL Meter* Sound Pressure Level (SPL) meter, reference sound comparison Android 50K+4.6/5.0 May-19 Free(A)

SoundPrint* Crowdsourcing-based approach to find quiet places Android 1000+2.7/5.0 Apr-19 Free

iOS - 4.1/5.0 Apr-19 Free

SPLnFFT Noise Meter* SPL with frequency analyzer, signal generator, dosimeter, etc. iOS - 4.7/5.0 Oct-18 3.59e(I)

Too Noisy Pro* Monitors noise levels in a closed environment, e.g., in classroom Android 1000+3.5/5.0 Feb-16 5.49e

iOS - 4.1/5.0 Jan-17 4.46e

Furthermore, extensive literature development on hearing protection using smartphone

technology exists. In terms of education to preserve hearing or perform hearing protection

interventions, in [

], the authors report on the use of technology-based interventions to improve

hearing protection in adolescent farmworkers. The study compares the use of technology (computer-

and smartphone-based) vs face-to-face training modalities for hearing conservation and protection.

The six-week study yielded statistically non-significant changes in the user’s attitude, behavior,

and knowledge in terms of hearing conservation education in three groups (computer, smartphone,

face-to-face). The results from pre- and post-intervention survey of 70 participants (only 50 participants

responded to post-intervention survey) established that the hearing conservation knowledge of

participants improved for all three groups, but fails to discuss if technology-based interventions were

better than that of face-to-face. Another article presented by [

] adopts a military hearing conservation

program namely, military hearing conservation programs (MHCPs) into a smartphone app. In addition

to listing and reviewing existing smartphone apps for hearing protection, the article discusses the

technical details of the development of the Warfighter’s Hearing Health Instructional (WHHIP) app.

The article lapses in critically evaluating the developed app both in terms of technical as well as

presents no data or results on the effectiveness of the developed app. Although, smartphone-delivered

hearing conservation training and educational apps on hearing protection can be a cost-effective

alternative mode to face-to-face training, particularly in a remote location setting, the effectiveness of

involving such technological tools is still not established [75].

Sensors 2020,20, 1725 10 of 21

The following articles feature the technologies and subsequent improvements for hearing-loss

protection: ref. [

] points out the technological advancements for hearing loss prevention. Herein,

in addition to listing some smartphone-based apps, the authors talk about the AI-based solutions

in hearables (such as smart headphones or earphones). The article also discusses the issues of

work-related noise and how to tackle it by employing technological tools to prevent hearing loss.

Similarly, ref. [

] explores the relation between noise-induced hearing loss and occupational noise

exposure, the study investigates the use of smartphones to measure sound exposure or noise in

occupational settings. In addition to highlighting some smartphone apps, the author conducts

multiple experiments using different combinations of microphones, occupational settings, and sound

measuring apps. In the opinion of the author, smartphones tend to overestimate noise exposure by

significantly lower margins making mobile-based audiometry an accurate alternative for noise-level

detection. [

] compare a Sound Level Meter app developed by the National Institute for Occupational

Safety and Health (NIOSH) in measuring industrial/mining sound levels as opposed to controlled

laboratory environments. The authors conclude that the use of apps in industrial/mining settings

as being useful with recommendations for additional validations. In their observational study, [

]

primarily determined if the smartphone app (SoundMeter Pro app) could be useful for detecting

dangerous sound-levels based on NIOSH guidelines. Secondarily, the study evaluates noise exposure

measurement in exercise spin classes, concluding that the exercise classes generate noise levels that

can induce hearing loss and that the use of mobile-based audiometry allows real-time monitoring of

noise exposures. Despite the fact that smartphone-based noise exposure detection offers viable and

accurate technique, and some smartphone apps for noise exposure detection have been validated in

literature [

], hearing healthcare professionals have to be involved in the process to ensure that these

technological advancements are properly employed to avoid hearing loss.

The literature on applicability and validation of hearing protection particularly for tinnitus

patients is almost non-existent. However, it is established that exposure of tinnitus patients

to dangerous levels of sound usually results in increased tinnitus symptoms, causing increased

tinnitus-related distress and anxiety. The commonly occurring hearing loss with tinnitus can further

attribute to increasing this annoyance and distress [

]. The aforementioned literature pertaining to

mobile-based audiometry and sound-level monitoring suggests that smartphone apps can enable

users to monitor sound levels with minimum error and take necessary countermeasures to prevent

dangerous noise exposures. Additionally, the smartphone apps highlighted in this subsection can

enable tinnitus patients in attaining necessary knowledge about managing their hearing loss with the

help of hearing conservation programs. The knowledge of current sound environment using these

smartphone apps can also help tinnitus patients in preserving the remaining hearing, and manage

tinnitus symptoms.

3.4. Hearing Testing Using Smartphones

Testing hearing or audiometry may be achieved via smartphone apps. Given that the audiometry

is properly performed, smartphone-based solutions may prove to be useful in resource-limited settings.

An ample amount of hearing testing apps exist in the smartphone market places. A list of apps

that provide hearing testing are given in Table 4. These apps can range from testing hearing on an

individual level to comparing testing capabilities with others (for example, family members or friends).

Furthermore, they can be used to test hearing on different frequencies, as well as to test hearing in

noisy environments.

A considerable amount of peer-reviewed literature has reported on testing hearing with the

help of smartphones. Some of this literature probes the applicability of mobile hearing testing

in young adults or children. The paper presented by [

] is a case in point, where the authors

outline a smartphone-based hearing screening method. The authors explore and compare their

proposed smartphone-based hearing screening app (Ear Scale app) with Pure-tone Screening (PTS) in

a sound-treated booth to test the hearing of school-age children. The detailed evaluations presented

Sensors 2020,20, 1725 11 of 21

in the paper suggest that the Ear Scale app was able to accurately measure hearing loss (moderate to

worse) in school children and that the hearing screening performed using the app showed positive

consistency with PTS. Similarly, Ref. [

] propose an Android-based app to screen the hearing of

pre-school-aged children. The proposed app showed children with different pictures to choose,

based on the word they hear. The predefined set of words, in turn, is describing the pictures heard

by children on different sound levels. The outcomes of the proposed methods were compared

with conventional audiometric methods as well as alternative smartphone-based audiometric apps.

The final developed mobile device-based screening system (PASS Speech Audiometry Version 2)

suggests that smartphone-based audiometry can be easily adopted to prevent and manage hearing

loss. Furthermore, smartphone-based hearing testing can also be a viable and cost-effective solution

for accurately conducting audiometry in community-based early childhood development centers,

particularly in poor communities [

]. To add to this, smartphone-based audiometry can also be used

to estimate pure-tone thresholds [84].

Table 4.

Apps for hearing testing (Free = royalty free, Free(I) = in-app purchases, Free(A) =

ad-supported, Free(I,A) = both) *Apps reported in literature.

App Name Description Platform Users Rating Update Pricing

Audicus Hearing Test* Quick hearing test at different frequencies iOS - 4.1/5.0 Oct-18 Free

Better Hearing Hearing test to identify inaudible frequencies iOS - 2.3/5.0 Sep-12 Free(I)

Hearing Test* Hearing test in normal and noisy environments shows results in audiogram Android 1M+4.4/5.0 Dec-16 Free

iOS - 2.8/5.0 Aug-13 Free(I)

Hearing Test Pro* Paid version of Hearing Test Android 1K+4.6/5.0 Dec-16 3.58e

hearWHO* Hearing test using headphones from WHO Android 10K+4.1/5.0 Mar-16 Free

iOS - 4.0/5.0 May-13 Free

Jacoti Hearing Center* Helps in tracking hearing and provides results using DuoToneTM technology iOS - 3.8/5.0 Mar-19 Free

Mimi Hearing Test* Determines hearing age based on hearing test Android 10K+3.0/5.0 Sep-18 Free

iOS - 4.6/5.0 Jan-19 Free

Signia Hearing Test* Hearing test to identify words in background noise Android 10K+3.0/5.0 Nov-18 Free

iOS - 2.4/5.0 Jan-19 Free

Sound Scouts* A game-based hearing test for children Android 1K+5.0/5.0 Mar-19 Free

iOS - 5.0/5.0 Mar-19 Free

Soundcheck* Screens hearing and shows results in easy to read format Android 10K+3.5/5.0 Jun-15 Free

iOS - 2.9/5.0 Jul-15 Free

Tone Generator Compares hearing with friends and family using customised frequency tones iOS - 3.8/5.0 Sep-16 Free(I)

Track Your Hearing* Helps in monitoring and keeping track of hearing loss Android 50+1.0/5.0 Feb-18 Free

iOS - - Feb-15 Free

uHear* Hearing test in normal and noisy environments iOS - 3.5/5.0 Oct-15 Free

Moreover, evidence of use of smartphone-based hearing testing in clinical settings has also been

reported. An evaluation study presented by [

] tests the performance of the hearScreen

app at two

primary health care clinics. The sensitivity and specificity analyses of the hearScreen

app suggests

that the smartphone-based hearing testing within clinical settings is n adequate tools. However,

the role of audiologists remain significant while interpreting data from these apps to make clinical

decisions [

]. Within an Infectious Disease (ID) clinic setting, another article evaluated the hearTest

app as a clinical utility and determined that smartphone-based hearing screening can be a valid

baseline tool [

]. The hearTest

app is further validated using calibrated supra-aural headphones

and inexpensive smartphones in [

]. In conclusion, the hearTest

app can be used to determine

valid air-conduction hearing thresholds. In another validation study [

], the hearTest

app was

validated for extended high frequency hearing thresholds, determining that calibrated headphones

while used in combination with the app provide accurate and reliable results.

Evidently, a critical aspect of smartphone-based hearing testing is the use of headphones

or earphones. Usually, prior to conducting a hearing test, users are required to calibrate either

device-provided or model-specific headphones (bundled), or any other non-bundled headphones.

The calibration is performed by a normal-hearing person in order to determine a reference sound

level for comparison. A comparison of pure-tone audiometry hearing thresholds with the hearing

Sensors 2020,20, 1725 12 of 21

threshold measured via smartphone is done in [

]. In this scenario, the comparison is done on

a smartphone calibrated using bundled headphones and biologically determined reference sound

levels. The authors report that hearing testing on smartphones with bundled headphones are highly

compatible with pure-tone audiometry. A detailed evaluation of four different headphone models

that are used with mobile-based hearing testing apps concluded that mobile-based hearing testing

produces audiologists-quality data when coupled with suitable headphones [91].

Although hearing loss is attributed to increasing tinnitus-related annoyance, the levels of hearing

loss in different tinnitus patients vary, particularly for patients whose tinnitus is caused by hearing

damage [

]. The smartphone apps reported in this subsection can help these tinnitus patients in

identifying their specific hearing loss to apply the best possible therapy (for instance, sound therapy)

and deplete tinnitus-related symptoms. Smartphone-based hearing testing apps have been reported

in peer-reviewed literature discussing and evaluating their applicability in different scenarios (for

example, clinical settings, remote urban locations), however, the validity of these apps is still under

argument [

]. Despite the fact that hearing loss is commonly occurring phenomenon with tinnitus

and different other disorders like hyperacusis and Meniere’s disease, the literature on the validation

of smartphone-based hearing testing apps is undeniably non-existent. Therefore, in our opinion,

a detailed validation of smartphone-based hearing testing apps is indispensable, specifically for

tinnitus patients.

3.5. Smartphones-Based Hearing Enhancement

The embedded microphone in the smartphone combined with headphones can sustain hearing

enhancement in patients who are suffering from hearing loss. In this subsection, we discuss the

literature and smartphone apps pertaining to hearing enhancement using smartphones. The list of

apps identified during the review process are listed in Table 5. It is critical to note here that for this

review, we do not cite literature that reports on the use of hearing aids, even if they are optimized or

tailored to be used with smartphone apps. For insights into hearing aids, we encourage readers to have

a look at [

]. In Table 5, we specify smartphone apps based on two major aspects, namely the simple

boosting of the audio signal or specific frequencies as well as the filtering out of distracting noise.

Recall that most smartphone apps provide accurate and reliable results while used in combination

with bundled headphones, therefore, we have limited the scope of this review to smartphone or

headphone combinations for hearing enhancement, particularly because most commercially available

smartphones come with bundled headphones.

The application of smartphones targeting hearing enhancement can range from smartphone-based

games, up to auditory training programs, all the way to implementing a digital hearing aid with

the mobile device. An example implementation of smartphones as digital aid is discussed by [

The authors employ an audio-signal processing technique to develop a smartphone app enabling the

device to be used as hearing aid. Even though the final developed app has limited real-life evaluation

and validation, the results suggest that the app has significantly low latency and therefore is a viable

solution for face-to-face conversation. [

] detail a smartphone app based on audio signal processing,

where three important and generally used modules in digital hearing aids (namely, voice activity

detection, noise reduction, and compression) are implemented. Although the article discusses the

technical details of implementing the digital hearing aid modules, the final developed systems are

not subjected to any evaluation and therefore no data or results on the accuracy of the implemented

algorithms are discussed.

Sensors 2020,20, 1725 13 of 21

Table 5.

Apps for hearing enhancement (Free = royalty free, Free(I) = in-app purchases, Free(A) =

ad-supported, Free(I,A) = both) *Apps reported in literature.

App Name Description Platform Users Rating Update Pricing

AUD-1* Improves sound clarity using signal processing techniques iOS - 1.8/5.0 Nov-15 6.26e

BioAid* Offers different amplifications for a personalized selection iOS - 2.3/5.0 Feb-15 Free

Ear Agent Sound enhancements using headphones Android 5M+3.7/5.0 Feb-19 Free(I,A)

Ear Booster Sound amplification using headphones Android 100K+3.8/5.0 May-19 Free(A)

EarMachine* Sound enhancing app by recording via microphones iOS - 3.7/5.0 Jan-17 Free

Ear Spy Pro Noise reduction and sound enhancement Android 50K+4.2/5.0 Dec-18 Free(A)

EasyHearingAid Hearing impairment assistance using different frequencies iOS - 2.0/5.0 Jan-15 0.89e

Hear Hearing enhancement and noise control with auto personalized adjustments iOS - 3.7/5.0 Feb-18 Free(I)

Hear Coach An app to increase and improve listening abilities using a game Android 5K+4.2/5.0 Mar-16 Free

iOS - 2.6/5.0 Nov-19 Free

Hearing Aid An app to record conversation and remove background noise iOS - - Apr-19 Free

Hearing Amplifier* Enhances microphone input and outputs to headphones iOS - 2.3/5.0 Jan-19 Free

HearYouNow* Sound amplifier for each ear iOS - 3.0/5.0 - Free

Jacoti ListenApp* Enables apple ear phone to improve sound clarity iOS - 3.1/5.0 Mar-19 Free

Petralex Hearing Aid* Incoming sound enhancement Android 100K+3.9/5.0 Apr-19 Free(I)

iOS - 4.3/5.0 May-19 Free(I)

uSound* Amplifies sounds based on profile created using hearing tests Android 100K+3.7/5.0 Jan-19 Free(I)

iOS - 3.7/5.0 Sep-18 Free(I)

Noise reduction can be a critical aspect in improving overall hearing enhancement experience.

Generally, the noise reduction is carried out using an algorithm (for example, Binaural noise reduction

algorithm [

]), or using an unsupervised or supervised classifier [

]. Ref. [

] proposes an app

that is capable of achieving real-time noise reduction of speech signals, particularly in noisy sound

environments. The app relies on the Wiener Noise Reduction algorithm and the authors report positive

effects of noise reduction via the proposed app based on objective and subjective evaluation. Analogous

to this, and implementation of a smartphone app to classify noise by unsupervised classifier is detailed

by [

]. The aforementioned modules used in digital hearing aid implementations (namely, voice

activity detection, noise reduction, and compression) can be combined with this noise-classification

app to further improve the audio signal processing pipeline.

Furthermore, in addition to the apps mentioned in Table 5, smartphone apps also exist as auditory

training programs to assist patients with hearing loss [

]. Alternatively, smartphones can be assistive

in improving auditory memory skills. Ref. [

100

] proposes the process of implementing a smartphone

app that enables improvement of auditory memory skills, particularly in children with hearing loss.

The authors report that six different smartphone apps were developed, for all of which the usability

tests were conducted, and the results suggest that the developed apps were suitable in improving

auditory memory skills for children efficiently.

Tinnitus is known to impact the quality of life of tinnitus patients. Although, the number of

patients who experience a drastic decrease in their life quality is some-what low [

], almost all patients

suffering from tinnitus are affected by the annoyance caused by tinnitus in different life situations [

101

For instance, the continuous perception of phantom sound in the ear, and the usually accompanying

hearing loss can negatively affect a person in a social interaction scenario or in a working environment,

resulting in reduced socialization [

102

]. The smartphone-based hearing enhancement apps can certainly

assist patients in improving and managing such situations and a cost-effective alternative to clinically

validated cochlear implants or hearing aids (both clinically validated techniques to improve the quality

of life of tinnitus patients [

103

104

]). Further, as these smartphone apps can be used as a digital

hearing aid, or alternatively by achieving hearing enhancement using sound amplification techniques.

However, it should be noted that our literature search and review didn’t reveal any study that validated

the use of hearing protection apps in the tinnitus context. There is a dire need for studies to validate

and compare smartphone-based hearing enhancement techniques with cochlear implants and hearing

aids. Additionally, the smartphone apps need to be validated in terms of applicability and their use in

Sensors 2020,20, 1725 14 of 21

tinnitus, as enhancing hearing or sound amplification—despite being beneficial—can inadvertently

cause further damage (sound is a major factor in causing tinnitus-related discomfort).

3.6. EEG Systems and Smartphones

Tinnitus is perceived as ringing or buzzing located in one, both or between the ears. However,

the underlying effects of generation and manifestation pertain to the complete auditory pathway and

are not completely identified until today. Despite the unknown, a general conception of tinnitus is the

idea that the central nervous system is involved, and that tinnitus has its own neural correlates [

105

Among others, oscillatory alterations have been identified in EEG studies [

]. Despite contradictory

results, there have been recent developments suggesting Neurofeedback (NFB) as a suitable treatment

alternative [106].

NFB is a non-invasive method, generally based on EEG recordings, which are analyzed in

real-time, visualizing certain aspects of brain activity (for example, frequency band power) as a

positive or negative feedback that enables users or participants to voluntarily control their brain

activity patterns. While its mechanisms of action are still under scrutiny [

107

], NFB seems to be a

viable candidate for interventions in tinnitus and other chronic diseases. Available NFB applications

in the open market are primarily offered for concentration and meditation exercises and less for the

medical field. Yet, we do not want to leave this point unconsidered, and thus we take a step back to

look at available EEG apps in the hope that future NFB apps, with scientific claims, could be developed

on this basis.

To assess the oscillatory fingerprint of diseases like tinnitus, EEG recordings were performed

in a laboratory setting so far. Recently, researchers are increasingly attempting to transfer EEG

recordings from this static to novel environment like the private setting (for example, at home).

This so-called “mobile EEG” is an increasingly active area including the development of brain-computer

interfaces (BCI) for a vast range of non-medical applications, such as gaming [108], meditation, sport

activities [

109

], and personal health, for instance ‘brain training’ like neurofeedback [

110

111

]. In this

section, we will identify the apps being offered in the context of mobile EEG recordings (see Table 6).

Over the past few years, research showed that the signals acquired via wireless mobile EEG

headset devices are similar to those obtained with standard EEG laboratory equipment and traditional

rating scales or diagnostic assessments [

112

113

]. Due to the increasing interest in mobile EEG

applications, our search revealed several EEG apps, but not many were designed for research or

medical applications. From the latter group, most apps require, or are designed for, specific kinds of

EEG headset devices. These devices run on wet or dry electrodes and typically include impedance

differential inputs, an electrode ground, as well as other principal features required for EEG recordings.

For a comprehensive review, readers can refer to an existing coverage [

114

]. Concurrently, the apps’

software either stores the raw data with a download option (EEG Analyzer, Muse Monitor, BrainLog)

or supports ’online data processing’-tasks, such as acquisition, recording, or breaking down the EEG

signal by different scalp potentials in either frequency bands (eegID) or in “cognitive and emotional

metrics” as it is advertised by other applications, for instance, MyEmotiv. An important advantage of

some of the apps is the open-source software code, which can be downloaded and adapted to personal

needs (for example, EEG 101).

Mobile EEG systems and their applications offer great potential, not only, but also for the field of

tinnitus. However, in the context of medical and health-related services, a quality criterion such as

the CE mark, has not yet been defined in mobile applications. It, therefore, seems important that, in

addition to an authority overseeing the application software, highly qualified players in the health-care

system should be involved in the creation of such apps.

Sensors 2020,20, 1725 15 of 21

Table 6.

Apps for EEG recording (Free = royalty free, Free(I) = in-app purchases, Free(A) =

ad-supported, Free(I,A) = both).

App Name Description EEG System Platform Users Rating Update Pricing

BrainLog Records brain activity, exports as .csv and stores in iCloud Muse iOS - 1.8/5.0 Nov-15 1.09e

EEG 101 Teaches users the basics of EEG while displaying their own brain data Muse brain sensing headband Android 10K+3.8/5.0 May-18 Free

EEG Analyzer Brain activity recorded and stored as .csv in Dropbox MindWave by NeuroSky Android 10K+4.0/5.0 Aug-14 1.79e

eegID Captures electrical activity of brain and stores in .csv MindWave by NeuroSky Android 5K+4.2/5.0 Mar-14 1.79e

iBrainEEG2 Brain activity analyzed in relation to functional connectivity network Biosemi Android 1K+4.4/5.0 Mar-14 Free

Muse Monitor Monitors EEG data and stores in .csv Muse Android 5K+4.5/5.0 Jan-19 16.99e

Muse iOS - 4.2/5.0 Jan-19 13.40e

MyEmotiv Capture, save and playback recordings of brain activity in six EPOC Android 5K+2.5/5.0 Apr-19 Free

“cognitive and emotional metrics” EPOC iOS - 2.1/5.0 Apr-19 Free

Persyst Mobile Mobile-phone–based EEG recorder Persyst iOS - 1.8/5.0 Jul-18 Free

4. Limitations, Future Work and Conclusions

Relevant literature search—we are aware that keyword-based search can have limited coverage,

because there may be relevant documents not matching the chosen keywords. Different search

results obtained by the same query terms applied on different data sources gave some hints that

query terms could be further optimized. We attempted to improve this by isolating keywords that

caused reduced recall, however, we believe that it can be further improved. Similarly, most of these

searches were performed using the keyword ‘tinnitus’, this, on one hand, increases the precision to

find tinnitus-related studies, however, on the other, it limits the identification of studies reporting on

closely related subject areas to tinnitus. For instance, adding the ‘hearing loss’ keyword in the search

criteria could benefit from increasing the recall. Furthermore, we thoroughly ensured the selection of

relevant literature based on primarily investigating the abstract and introduction for relevance, and

secondarily based on the content of the paper. Again, we are aware that this process is subjective and

can probably be further improved.

Identifying relevant apps—another limitation of our proposed work constitutes the restricted

search of relevant apps in only two app stores, namely Google’s Play Store and Apple’s App Store.

Even though we justify this restriction, there is a slight chance that our work could benefit by exploring

other app stores, like Amazon’s and Samsung’s app stores. Although unlikely, 3rd party independent

app stores like Aptoide or F-Droid may contain previously unseen apps. During our searches, we

identified apps which were relevant for this review and were part of Google’s Play Store or Apple’s

App Store at one point of time, however, they were removed from respective app stores due to policy

conformation issues. Usually, removal of an app from these app stores is properly justified, however,

these restrictions can sometimes be inconsistent. Furthermore, to include an app in this review, we

inspected the app description and a selection of a few top-rated comments from users. This approach

is subjective and highly relies on the knowledge of the inspector about the domain and can be further

improved by collecting opinions from domain experts as opposed to general users.

For prospective work, we primarily aim to extend our work by reviewing internet- and

computer-based behavioral therapies applied directly in the context of tinnitus research. Herein,

an additional focus would be to include studies that report on the use of auxiliary and peripheral

sensors in assisting therapeutical solutions. For instance, the use of smartwatches or wristbands to

acquire physiological attributes of patients suffering from tinnitus could be additionally included.

Secondarily, as future work, we plan to extend our work by addressing psychological conditions

that are closely related to tinnitus. In view of this, the objectives of the study would be to identify

smartphone-based solutions, as well as internet- and computer-based therapeutical solutions offered

for the said complications. Furthermore, the study will report on the importance of highlighted

therapies and opinions of smartphone-based solutions from the perspective of patients.

In conclusion, the review presented in this paper highlights the impact of mobile applications

and mobile crowdsensing platforms, specifically within the context of tinnitus research. We identified

and investigated a wide array of heterogeneous apps heavily invested in supporting and controlling

tinnitus symptoms, understanding tinnitus, and monitoring patients suffering from tinnitus. Primarily,

Sensors 2020,20, 1725 16 of 21

we highlighted the available mobile apps that could be beneficial for a patient in mitigating or masking

annoying phantom sounds. We further explored different smartphone-delivered CBT therapies that can

be adopted by tinnitus patients to manage stress and anxiety accompanied by tinnitus. As significant

and continuous exposures to dangerous levels of sound are critical aspects in increasing tinnitus

symptoms or causing them, secondarily, we scrutinized mobile apps that are helpful in monitoring

noise levels and noise exposure, including apps that notify the user of dangerous exposure. Moreover,

we inspected apps that are useful in testing hearing. This is beneficial for patients suffering from

tinnitus by allowing them to monitor the hearing loss commonly occurring with tinnitus. Furthermore,

we explored and presented apps that provide assistance to patients suffering from hearing impairment.

For all categories, we not only provided a list of available apps but also reviewed relevant literature

documenting the usage and role of those apps.

Author Contributions:

M.M. undertook the database searches, cataloguing, conception, draft, and revision of the

paper. C.R. helped with writing Section 3.6. P.N. and R.P. helped with writing Section 2. A.D. helped in writing

and reviewing Section 1. W.S. and M.R. helped by critically revising the manuscript. F.J.H. contributed by helping

in writing Section 1, critical revisions, and final approval of the manuscript, as well as supervision of the entire

review. All authors have read and agreed to the published version of the manuscript.

Funding:

This publication is a result of research supported by funding from the European Union’s Horizon

2020 research and innovation programme under the Marie Skłodowska–Curie grant agreement number 722064

(European School for Interdisciplinary Tinnitus Research, ESIT) [115].

Acknowledgments: Thanks to Gerhard Habiger1for revieweing the manuscript.

Conflicts of Interest: The authors declare no conflict of interest.

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