# Telepresence Social Robotics towards Co-Presence: A Review
## 1 Introduction  
Telepresence robots are becoming popular in the context of social interactions. Typically, these systems enable people to look at a distant place via teleoperating a robot and interacting with another person at a remote location using the built-in communication devices. Some relevant applications include health care, elderly assistance, autism therapy, guidance, and office meetings [1, 2, 3, 4, 5, 6, 7]. This literature review aims to gather knowledge to help roboticists design improved user- and environment-adaptive systems and technical methods that contribute to enhancing the sense of presence or co-presence via social robot mediation. Reviews have addressed user-adaptive systems [2, 8] and environment-adaptive systems [9] for social robotics (in which the robot is generally an autonomous agent serving the bystander user). However, we further explore telepresence social robotics, with an emphasis placed on the relationship between the robot's operator and the bystander user. Within social telepresence robots interactions, two types of human psychological experiences can be considered (see Figure 1). The first one involves the _remote user_, in which he or she should sense being in the _local environment_ (i.e., telepresence) [10, 11], and the second type involves the _local user_, in which ultimately he or she should sense that the remote user is with him or her in the local environment (i.e., _co-presence_) [12, 13]. This research will focus on this last type of interaction, or how to enhance the sense of _co-presence_ via robot mediation. To clarify the role of each agent in the interaction, the following terminology is adopted:  
1. Mobile robotic telepresence (MRP) system: remotely controllable mobile platform with video conferencing equipment that allows remote users to navigate within a localenvironment and socially interact with other persons. These systems can incorporate semi-autonomous functionalities to mitigate operation loads such as navigation aids, points to follow, and obstacle avoidance. 2. Robotic telepresence (RP) system: remotely controllable or semi-autonomous robotic device with video conferencing capabilities that enable social interaction with people in the local environment without locomotion means. Remote users can explicitly control parts of the robot (e.g., the head's panning, swinging, tilting, eye gazing, and facial expressions, as well as arm or hand gestures) or enable some semi-autonomous behaviors (e.g., blinking, face tracking, eye saccade, and breathing). 3. Remote user: user that steers the robot from a distant location or simply connects to the robot through a computer interface. 4. Local user: user that shares the physical environment with the robot (bystander). 5. Local environment: environment shared by the local user and robot. Presence is often defined as the sense of _being there_ in a mediated environment [14; 15]. Additionally, [PERSON] [16] differentiates presence (virtual) from telepresence (experiential). _Presence_ describes the experience of being present within a virtual world, while _telepresence_ refers to the sense of being in a mediated remote real environment. _Co-presence_ has been used to refer to the _sense of being together_ with others in a mediated (either in remote real or virtual) environment [17; 18; 19; 13]. [PERSON] introduced the _telepresence_ concept in the teleoperation context to describe the phenomenon in which a human operator feels physically present at a remote location through interaction with the human's sensing systems [11] (i.e., \"through actions of the user and the corresponding perceptual feedback provided by the teleoperation technology\") [10]. [PERSON] and [PERSON] [20] developed one of the first telepresence robots and referred to it as a personal roving presence (PRoP) device. The goal was to \"provide a physical mobile proxy, controllable over the Internet to provide tele-embodiment\".