# Effects of Voice and Lighting Color on the Social Perception of Home Healthcare Robots
## 1 Introduction  
The emerging application of social robots has led to increasing systematic research on human-robot interaction (HRI) [1, 2, 3]. Robots that are perceived to be consistent with their professional roles and conform to user expectations are more accepted by users. Healthcare robots are expected to play crucial roles in people's daily lives in the future [4]. Such robots can be used in hospitals, care centers, and homes to manage users' health and give them care services or companionship [5]. In contrast to the service robots used in malls, which interact with people for short periods, healthcare robots tend to interact frequently with users for extended periods. Therefore, people's perception of and interaction with healthcare robots have become increasingly crucial topics [6]. On the basis of the computers-are-social-actors (CASA) paradigm [7], studies have found that a robot's social cues during human-robot interaction can affect people's social perception of the robot [8, 9, 10]. People tend to categorize the gender and age of a robot in accordance with the social cues given by the robot [11, 12, 13]. Such categorization is particularly crucial during the first encounter between a human and a robot [14]. After a robot is assigned social membership, people are more likely to treat the robot as a part of their social group and apply social norms to it. Thus, the social perception of a robot during the first HRI can strongly affect people's subsequent interaction experience with, trust in, and acceptance of the robot [15]. If healthcare robots trigger social perceptions that are more favorable, they are more likely to be accepted by users, which leads to fewer difficulties in subsequent HRI. For example, a study on gender effects related to robots found that users associate stereotypes of women with robots that are categorized into the female group [13]. Such robots might be considered caring and compassionate and might be accepted in industries that favor these characteristics [10]. A social robot's voice,facial expressions, and appearance are crucial social cues [16] that can influence a user's social perception of it [17; 18]. The manipulation of these social cues can produce a stable social perception of robots and influence users' acceptance of robots [19; 20]. [PERSON] and [PERSON] [12] measured the effects of a robot's facial stimuli on social perceptions of the robot and discovered that people highly favor contact with robots that appear humanlike and feminine. [PERSON], [PERSON] [21] investigated how robots' eye gaze affects older users' social perception of robots. [PERSON], [PERSON] [22] explored users' affective evaluation of robots' voice and found that users judge whether a robot is suited to its professional role on the basis of its voice during their first interaction with it. Verbal and nonverbal cues influence the social perception of robots [23]. Relevant studies have examined the effects of a single type of robot cue (visual or verbal) on the social perception of robots; however, research investigating the effect of matched verbal and visual cues [23] of robots on the social perception of those robots is lacking. Therefore, studying visual or verbal cues in isolation may lead to perceptual mismatches, which were found to even cause user disgust. The influence of matching between the aforementioned cues of a robot on social perceptions of the robot must thus be explored. Verbal interaction is the most intuitive HRI method. The voice carries considerable socially relevant information [24], and the voice of intelligent robots can strongly affect people's social perception of them [10; 13; 25]. People have preferences for certain types of voices, and they associate stereotypes with these voices [26]. For example, men and women consider a relatively low-frequency voice to be attractive and dominant [27]. By contrast, a relatively high-frequency voice is considered emotional and immature [28].