## 4 Results
### Interaction with an Agent
#### 4.3.1 Interaction Devices  
An interaction device is a platform that visualizes AR content to the agent and it may also receive input from the agent. The interaction device can have many forms, such as a mobile device (e.g., smartphone, tablet PC) [10; 11; 33; 34; 35; 36; 37; 39; 40; 42; 44; 46; 48; 50; 51; 52], HMD [12; 38; 41; 45; 49], PC/TV monitor [41; 43; 47], and projector [41].  
The most commonly implemented interactions between an agent and interaction device are as follows: (1) moving the interaction device to see AR content, (2) sending commands to control IoT devices or other entities, (3) navigating the data sent from IoT devices through a user interface on the interaction device, and (4) moving the interaction device to recognize the agent's hands. As an example of the first and second interactions,  
Figure 5: Interaction between an agent and an interaction device, IoT device, and another entity.  
Figure 6: Interaction usage status for each reviewed study.  
a smartphone in the MI system that was proposed by [PERSON] and [PERSON] [11] can identify a lamp in a shop by analyzing the smartphone camera's feed. The power of the lamp can be controlled by touching a button on the screen of a smartphone. An IoT device is attached to the lamp that sends the power status of the lamp to the smartphone while allowing the agent to control the power of the lamp. As an example of the third interaction, [PERSON] et al. [33] developed a mobile application that visualizes the temperature data obtained from IoT devices. The temperature data are represented by emojis that are based on the temperature level. The emojis are placed on the IoT devices, while graphs of device data that are correlated with each emoji are displayed on the mobile screen. The agent can obtain detailed information regarding the IoT devices that the application recognizes by touching the graphs. As an example of fourth interaction, four out of five studies [12; 41; 45; 49] that used an HMD as an interaction device utilized it to identify the hand gestures of an agent. The exception was a study by [PERSON] et al. [46], who used a mobile device instead of an HMD to detect the agent's hand positions to display the data that were collected from IoT devices on the interaction device when the agent's hands were placed at a specific location.  
Although the aforementioned interactions are commonly used in MI systems, there also exist interactions that are used for specific purposes and in dedicated environments. For example, an agent can play a simple guessing game on a smartphone in the MI system proposed by [PERSON] et al. [39]. Non-AR 2D user interfaces are used to receive answers from the agent, while a 3D AR character is used to represent the current temperature and CO\({}_{2}\) levels while using dedicated outfits. In the MI system that was proposed by [PERSON] et al. [38], the interaction device is an HMD that produces sound alarms when the sensor data (e.g., temperature, humidity, CO\({}_{2}\), O\({}_{2}\), heart rate) that were collected by IoT devices exceed certain levels. The purpose of the sound alarm is to alert the agent about danger. In some MI systems, interaction devices are connected to a stationary camera to monitor specific objects or stream a certain viewpoint. The MI system that was proposed by [PERSON] and [PERSON] [47] utilizes a PC monitor to observe crops that were planted on a farm. In their MI system, AR content is displayed near the position at which the MI system recognizes crops using regions of interests that were detected by a computer vision technique. In the MI system that was proposed by [PERSON] et al. [43], a television is the interaction device that is connected to a stationary camera to stream the space in which the agent moves smart objects on a smartboard. The location of AR content is determined by movement of the smart objects detected by light density resistors under the smartboard.