# Effectiveness of Augmented Reality in Stroke Rehabilitation: A Meta-Analysis
## 3 Results and Discussion
### AR Technique Overview  
#### 3.1.1 AR Technique for Upper Limb Rehabilitation  
Nine studies used AR to improve upper limb function. The main type of AR intervention was games, which were specifically described in the literature [26, 27, 28, 29]. They provided games to increase motivation, overcoming gravity for patients. Specifically, [PERSON] et al. proposed the ARS; that is, a simple AR system for home rehabilitation after stroke [26]. The authors presented two versions: a computer game, and a more advanced version that incorporates a control tool (a computer mouse/arm skate) to increase the physical effort associated with reaching tasks. Additionally, the system includes feedback or factors such as a game score, intellectual stimulation, and social interaction during group play. [PERSON] et al. developed a framework called post-Stroke Interactive and Entertaining Rehabilitation with Reactive Objects (SIERRA) [27]. In order to increase the patients' per  
Figure 2: PRISMA study selection flow diagram. ception of interaction with virtual objects in the environment, they embedded vibrotactile actuators in tangible objects used in the recovery exercise of the SIERRA framework. In the two above AR game systems, they have relied on tracking methods for a prepared environment using the marker-based AR technology that the virtual item is showed if the corresponding marker is detected. Specifically, a pattern using black and white (B/W) fiducial markers is employed for the markers in the above AR systems. This technique is applied in many AR systems because it enables more precise and faster tracking. However, poor lighting environments and marker occlusions are some factors that induce difficulties in marker recognition for the AR systems based on marker tracking. Additionally, screens-based AR technologies are used in these AR rehabilitation systems. The AR system can give a high quality of present and embodiment which helps patients to have more realistic feeling. In order to enhance the sense of immersion, [PERSON] et al. proposed an AR rehabilitation system using the head-mounted display (HMD) device [29]. Besides, this system includes a Leap Motion, an HD Webcam, a Microsoft Kinect v2 sensor connecting with a laptop. The leap motion is utilized for contactless tracking of the hand. Furthermore, the combination of contactless tracking and 3D rendering to overcome the limitations of gloves, makers occlusions in the 3D environment based on the Microsoft Kinect v2 sensor. It helps the patients feel natural when interacting with virtual objects. Three games are designed to assess the speed, hand opening abilities to various size objects, and obstacle avoidance. However, the use of screen-based AR technology and HMD device in these types of AR systems has the limitation of the field of view (FOV) due to the monitor size, the distance between the display and the observer. In addition, discomfort, the weight of the device, and poor brightness of micro-displays are the technical problems of the HMD device. To overcome the narrow FOV limitation of the screen-based AR technique and wearable HMD, [PERSON] et al. reported an AR rehabilitation system using projector-based spatial displays [28]. This technique provides a large FOV to the patient using front-projection to display images directly on physical surfaces. The AR system is based on the commercial Fruit Ninja game. The game activity was displayed on a tabletop using a projector. When slicing the virtual fruit targets, the patients could directly gaze at the real-hand movement on the tabletop. The system can provide feedback as the game scores to motivate the patients during rehabilitation. Another type of AR intervention was based on the principle of traditional mirror therapy for upper limb rehabilitation. Conventional mirror therapy uses a real mirror to show the normal movement in the affected limb based on the movement of the unaffected limb in front of a mirror.