# Effects of Voice and Lighting Color on the Social Perception of Home Healthcare Robots
## 1 Introduction
People judge whether a speaker conforms to a stereotype by listening to their voice, and on the basis of this judgment, they feel affection or disaffection for the speaker [26; 29; 30]. Despite the importance of verbal communication in HRI, relying on verbal communication alone is insufficient, particularly in noisy environments or when a robot interacts with a user who has impaired hearing or is located far away [31]. In addition to the effects of verbal interaction on HRI, the effects of visual feedback on HRI should be examined [32]. Visual feedback in human interactions occurs mainly through nonverbal cues, such as gestures and facial expressions. However, only a few social robots currently have the ability to present vivid facial expressions and behaviors; thus, most robots use lighting for providing visual feedback [33]. It is commonly seen that when a robot is interacting with a user, a light flashes in the robot's eyes, and this light acts as interactive feedback. Researchers have indicated that lighting can allow a robot to exhibit visual feedback cues and express its inner state, thereby facilitating HRI [31; 32; 33; 34]. Lighting is often installed in the eye of a robot (e.g., Nao and Pepper) to improve its engagement with users. A robot can convey nonverbal information, such as \"I am talking to you\" and \"I am listening to you\" to a user, and this information might affect the user's social perception of the robot. Animation patterns, lighting speed, and lighting color are crucial factors that affect the perception of robots [32]. [PERSON] et al. [35] analyzed several patterns of blinking lights used in intelligent robots during verbal communication with humans and investigated the effects of the lighting animation and speed. The color of lighting is particularly crucial because colors are strongly related to people's feelings and life experiences and can influence their social perceptions of robots. Studies have shown that recognition of facial emotional states can affect social perception [36]. The six basic emotions (anger, disgust, fear, joy, sadness, surprise) identified by [PERSON] [37] have been favored by researchers investigating the emotional expressions of robots. Studies have observed emotional associations with colors. For example, [PERSON] and [PERSON] [38] developed a color circle that matches the circular model of emotions proposed by [PERSON] [39]. Moreover, [PERSON], [PERSON] [40] manipulated the color luminosity of a robot's body to express the emotions of the robot. They found that the hue value represents basic types of emotion (anger--red, anticipation--amber, joy--yellow, trust--green). Blue lighting usually causes people to feel comfortable and safe [41], whereas red lighting can invoke positivity (e.g., feeling strong) or negativity (e.g., associations with blood and aggression) [42]. These color-associated feelings can be paired with verbal cues to create a stable social perception of robots to ensure that people have a suitable image of robots in their minds. On the basis of [PERSON] [43]'s social-cognitive dimensions (sociability and competence), our previous study [44] established user expectation coordinate systems for robot applications (Figure 1) and explored the effect of matching between the verbal and visual cues of robots on the social perception of these robots within the context of shopping reception, education, and companionship [45]. Studies have not yet examined the aforementioned effects for healthcare robots, of which users have high expectations. Therefore, the aim of this study was to explore how home healthcare robots' verbal (voice type) and visual (lighting color) cues can be matched and how this matching influences older and middle-aged users' social perception of these robots. The results of this study can be used as a basis to derive generalized design guidelines for social robots to be used in various occupational fields.