## 3 Presentation to the Participants
### Virtual Reality Systems/Devices
In this experiment, three conditions are tested: (1) direct facial motion tracking without any modification; (2) exaggerated facial motion; (3) dampened facial motion. The result shows that the participants exhibited more positive nonverbal responses for exaggerated facial motion, while there was no difference in verbal responses, which supports the authors' hypothesis that an animated avatar with more exaggerated facial expressions can enhance participant engagement and comprehension. The virtual avatars used in most studies were produced using 3D animation platforms such as Unity or Vizard. Some studies chose to intentionally use 2D avatars either for comparison or to minimize sensory overload for participants with ASD. Yet some studies chose to use animated photos of real persons as avatars, such as FaceSay [53]. For virtual avatar based serious games and programs, it is essential to produce avatars that can be used to elicit stimuli appropriate for study. Undoubtedly, facial expressions are one of the most important elements in avatar production. In [52], the two-dimensional active appearance models(AAMs) are used to track a therapist's facial motion. In the first step, AAMs are used to build a set of models based on the appearance and shape of the person's face. The learned models are used to produce an AAM mesh. This mesh is then used to track the facial motion of the person and to retarget to the avatar face. In [28; 37; 39; 40; 41; 57], the Vizard Virtual Reality Toolkit, a commercial product from WorldViz ([[http://www.worldviz.com/vizard-virtual-reality-software/](http://www.worldviz.com/vizard-virtual-reality-software/)]([http://www.worldviz.com/vizard-virtual-reality-software/](http://www.worldviz.com/vizard-virtual-reality-software/))) was used to produce the avatars in the study. The toolkit contains a PeopleMaker program, which users can use to custom design morphable 3D heads for avatars for different emotion expressions. In [39], two different experimental paradigms, flashing paradigm and animated paradigm were used. The flashing paradigm involves three scenarios: (1) flashed schematic eyes, where the target event consists of eye balls slightly rotated while the non-target event consists of two eyeballs on the background screen; (2) flashed face with eye position change, where the target event consists of eyes gazing to the face's right and the non-target event consists of a face facing straight front; (3) flashed face with eye and head position change, where the target event consists of the face facing towards the left while the non-target event consists of a face facing direct forward. The animated paradigm involves with two scenarios: (1) animated 3D body with gaze change in one avatar, where the target event consists of the avatar head turning to the right side, and the non-target event consists of the avatar head turning to the left side; (2) animated avatars with gaze change in four avatars, where the scene contains four different avatars and the target event consists of the head of the avatar at the top row turning to the right while the non-target event consists of one of the avatars turning to the right. In [40], the Vizard Virtual Reality Toolkit is also used. Instead of using the built-in avatars, they chose avatar heads from a database from the Virtual Human Interaction Lab at Stanford University. These avatar heads were converted from 2D photos of teenagers to 3D models using the 3 DMeNow software (the company that created the software has ceased to exist). The authors further customized the complexion of the avatar heads using GIMP (GNU Image Manipulation Program), which is a free open source program. The study developed an emotion model that varies the expression from angry (the negative extreme) to happy (the positive extreme). In addition to face expression variations, an avatar can make gestures based on bone-kinematics, and walk around the scene.