## 3 Presentation to the Participants
### Social Robots  
Many studies have employed humanoid robots for treatment plans for children with ASD [66; 67; 68; 69; 70; 71; 72; 73; 74; 75; 76; 77; 78; 79]. However, some research has used non-humanoid robots [80; 81; 82; 83; 84]. To employ humanoid robots in autism studies, one has to overcome two technical challenges: (1) how to control the movements of the robot, and (2) how to obtain the input from the participant. Unlike virtual avatars, where mature technologies exist to enable high fidelity animation of both facial expressions and body gestures, which are essential to facilitate closed-loop autonomous treatment programs, socially assistive robots used for autism studies so far are scripted in a very limited way (such as raising an arm etc. ), presumably due to safety and cost concerns. Furthermore, the use of a social robot is meant to facilitate natural user interaction where the participant would engage in verbal conversations and/or use his/her gestures while doing so. In contrast, a virtual avatar based system can equip the participant with a keyboard and mouse, or a touch screen, which allows the participant to provide his/her input/response to a question by typing, clicking, and touching by hand. There have been efforts towards an autonomous robotic system. Similar to a virtual reality based system, the eye gaze of the participant with respect to the robot can be detected using eye/head tracking devices, such as a remote desktop eye tracker [85] or a head-mounted eye tracking device [86]. Accurate tracking of eye gaze could enable partial autonomous operation of the treatment program via a social robot. Some studies have also enabled some form of speech recognition functionality. It is limited because for higher recognition accuracy, only scripted simple voice commands can be recognized. There is still a long way to go to support unscripted conversations between a robot and a participant. There is also work on using cameras to track facial expressions [87; 88] and gestures made by a participant to understand the emotion of the participant and to allow the participant to give commands to the robots for increased degree of interaction between robots and participants [11]. Despite recent progresses made, such as motion and eye tracking [89; 90; 91], in social robotic research, the Wizard of Oz scheme remains the dominant approach to give an illusion that the robot can capture and understand the participant input/response and react/adapt properly while in fact the expression and motion of the robot is controlled, and the user input is captured by a therapist and/or technician. Many different types of robots have been employed in this line of research, including both humanoid robots and non-humanoid robots. Some robots are stationary in that they do not move around even though they can move their arms, legs and heads in certain ways. Some other robots are mobile in that they can be instructed to move around or even to follow the participant [11]. Most robots are equipped with cameras (for object recognition), microphones (for voice commands or speech recognition), and speakers. Some are equipped with tactile sensors at the head and head to sense touching. Humanoid robot Nao from Aldebaran Robotics Company is one of the most popular robots used in autism studies [85; 92; 93; 94; 95; 96; 97; 98; 99]. Nao is a child-sized robot with plastic body (58 cm tall and 4.3 kg weight). It was used in [92] for joint attention and imitation study, in [85] for joint attention study, in [95] for interventions on repetitive behaviors and affective states, in [96] for interventions on verbal communication skills, and in [97; 100] for intervention on imitation and interpersonal synchrony of children with ASD. In [95], an additional mobile robot called Rovio from WowWee was used. Another humanoid robot Zeno R-30 was used in [101] to facilitate imitation training for children with ASD. Zeno R-30 is also a child-like robot produced by Hanson RoboKind. Zeno must be controlled by a separate computer.