While most of the studies are about how to help parents to take care of their children with ASD, it is also important to help parents to cope with the tremendous stress while taking care of their children with ASD. A StressLess mobile app was developed and its efficacy was studied in a randomized controlled trial ^[4]. The design of the StressLess app was guided by the principles of cognitive behavioral training to provide psychoeducation and interactive exercises.

3.2. Teacher Training Apps

In ^[5], the Map4speech mobile app was used to train teachers in a very similar fashion to the authors’ earlier study ^[6], where the app was used to train parents to improve the functional communication of their children with ASD. In ^[7], the usability and efficacy of a mobile app called IEP-Connect were reported. IEP in the app name stands for individualized education program. The study was conducted in the context of classroom education. The app was designed to select the most optimal motivator for teachers and therapists to use based on the recorded problematic behaviors of their students. The motivator selection is based on an applied behavior analysis and incorporates reinforcement learning. The decision making is based on Markov decision processes. The effectiveness of the motivator selected is measured by the student motivation after the selected motivator has been applied.

3.3. Autism Support Apps

3.3.1. Communication and Social Interaction

In ^[8], a mobile app called MyCalendar was used to help children with ASD who have limited verbal skills to communicate with their teachers in schools and with their families at home. The app presents a calendar view to the users, where the children, teachers, and family members may add photos and videos to the calendar each day. The mobile app encourages the children with ASD to communicate with the teachers at school and the family members at home. The app also allows the users to annotate the photos and videos, which make the app a visual diary of the children with ASD. That said, the main goal of the app is to encourage children with ASD to communicate with their teachers and family members, and reinforce the value of social interaction and emotional bonds via replaying and modeling positive social interactions.

3.3.2. Independent Living

Several mobile apps have been developed to help individuals with ASD to achieve independent living. These not only include the training of children with ASD to perform daily routines such as brushing teeth and putting on clothes, but also include the training of more demanding skills such as planning for trips and medical appointments, self-management skills, vocational skills, and adaptive skills. In ^[9], the design of a mobile app called AutiAct was reported. The app helps a child with ASD to learn some basic daily routines at three different difficulty levels: easy, medium, and hard. The easy level consists of the daily routines of washing their hands and face. The medium level consists of the daily routines of brushing their teeth and flushing the toilet. The difficult level consists of one daily routine of putting on shoes. For each daily routine, a training video is provided in the app. The underlying mechanisms adopted in the app are augmentative and alternative communication ^[10] and video modeling ^[11].

3.4. Educational Apps

In ^[12], a set of criteria was developed to assess the mobile apps (limited to the Android platform) for teaching children and adolescents basic instrumental skills (oral language, reading, writing, and mathematics). The study found 88 apps (English and Spanish) from the Google Play Store. The criteria include three dimensions: design and form (availability of the app, ergonomics, usability, popularity, and accessibility), content (coverage of key elements in pronunciation, reading, writing, and math, guide on using the app, audio quality, and safety), and pedagogical aspects (interactivity, suitability of pace and learning, and assessment). Some of the criteria could provide guidance on the development of new mobile apps that target instrumental skills. However, the criteria appear to have ignored the specific needs from children and adolescents with ASD. In a similar study ^[13], the same research group evaluated 155 Android apps using the same set of criteria.

3.5. Data Collection Apps

Traditionally, diagnosis and assessment of symptom changes are largely based on retrospective reports from caregivers of individuals with ASD. Such an approach may introduce errors in reporting because of the necessity of recalling past behaviors of the individuals with ASD. It is much more desirable to collect data in real time or nearly real time. In ^[14], an observational study on caregivers’ daily reporting of autism symptoms using a web and mobile app called My JAKE (short for Janssen Autism Knowledge Engine) was reported. The caregiver is expected to first complete the medical and developmental history of the child with ASD in the app. Then, on a daily basis, the caregiver is required to complete the autism behavior inventory, which consists of 73 items that cover the symptoms and behaviors of the child with ASD. The app also allows the caregiver to log additional items using the journal and event tracker. Furthermore, the app can be connected to the Microsoft health vault. The usability of the app was evaluated using a human subject trial with 144 caregivers.

4. The Mechanisms of Mobile Apps to Improve User Engagement

4.1. General Purpose Mechanisms

Gamification

Gamification refers to adding game design elements in the mobile app. Games by definition are voluntary and enjoyable. Games are a special form of play in that games are intrinsically goal-oriented and they are bound by predefined rules ^[15]. Another element of games is feedback. Feedback informs the player whether or not the rules are followed and whether or not the goal has been reached. The mechanics, dynamics, and aesthetics (MDA) framework has been widely adopted in game development ^[16]. According to the MDA framework, game design is experience driven instead of feature driven. The game itself resembles more of an artifact instead of media. The content of the game is its behavior exhibited via the interaction with a player. The relationship between game mechanics, game dynamics, and game aesthetics is illustrated in Figure 3. Aesthetics captures the user expectations of the game. In ^[16], eight aesthetics properties are defined, including sensation, fantasy, narrative, challenge, fellowship, discovery, expression, and submission. A game does not need to satisfy all eight aesthetics properties. Game mechanics are mostly defined by the rules of the game, which are inevitably game specific. Some common game content may also be considered as part of game mechanics, such as points, levels, and leader boards ^[15]. Game dynamics refers to how the game is implemented in a system that would give the player aesthetic experiences. Although game dynamics are game specific, there are some common elements that help achieve game aesthetics, as shown in Figure 3. Feedback is an essential component of game dynamics. Games typically incorporate some form of virtual reality, which helps achieve user sensation and fantasy. Incorporating time pressure during game play and having an opponent would increase the challenge of the game. Supporting multiple players to cooperate during game play would create fellowship experience. Allowing customization of the game environment, such as allowing the user to select an avatar or even create a unique avatar, would help satisfy the players’ expression desire.

4.2. Virtual Reality

Virtual reality refers to the immersive and interactive environment of a synthetic world ^[17]. The synthetic world might incorporate elements of the real environment to different extents. In ^[17], this is referred to as a virtuality continuum. For example, the virtual reality environment may use smartphone cameras and sensors to incorporate the user’s face or movement into the virtual reality scene. That is why some publications use the term “augmented” reality. Traditionally, virtual reality is achieved via expensive 3D immersive systems such as CAVE and head-mounted goggles. Recently, devices have been made to use a smartphone in a way similar to head-mounted goggles. The Virtuoso mobile app is used in this way ^[18], and it was used to train adults with ASD adaptive skills. However, a virtual reality user interface does not have to be fully immersive to be effective, which has been confirmed in many autism studies ^[19].

4.3. Autism-Specific Mechanisms

Several studies incorporated autism-specific mechanisms to improve the engagement level of the mobile apps. In ^[20], the app design allows the user to choose an avatar that matches their own restricted interest. As a result of the alignment with the child’s restricted interest, the mobile app (called Sidekick!) was able to maintain the motivation of the child with ASD and improve the treatment adherence in therapy sessions, schools, and at home.

5. Guidelines Followed in the Mobile App Development

Three studies provided detailed processes in the design and development of the mobile app ^[21][22][23]. All of them followed a user-centered design (UCD) process ^[24]. UCD refers to a loosely defined process that has the following elements: (1) understand the users; (2) actively involve the users when defining the requirements; and (3) iterative design and evaluation. To understand the users and to discover the requirements, various instruments have been used, including questionnaires, interviews, focus groups, and observations. Ideally, the targeted individuals with ASD should be the subjects of these instruments. However, it might not be practical to directly involve children with ASD in the design process due to their disorders. Some of them might be non-verbal. As such, studies often involve parents, teachers, and therapists of the children with ASD. Experienced software developers for this type of app have also been involved ^[21][22]. Each of the three studies developed or followed a set of guidelines to make the app a good fit for the target autism population and for the specific application objective, as illustrated in Figure 4. The development of the PuzzleWalk app ^[23], which is an app promoting physical activities for adults with ASD, included ten guidelines as shown in the left column of Figure 4. The development of the SimpleTEA app ^[21], which is a serious mobile game for improving communication in children with ASD, considered four major perspectives: user sensitivity, user safety, user engagement, and game playability, as shown in the middle column of Figure 4. The development of the PlanTEA app ^[22], which is an app supporting children with ASD to attend medical appointments, was guided by the AutismGuideline proposed in ^[25], as illustrated in the right column of Figure 4.