# Effects of Voice and Lighting Color on the Social Perception of Home Healthcare Robots
## 4 Discussion  
A healthcare robot's social cues can affect users' perception, experience, acceptance, and rejection of it. In this study, we examined the effects of a healthcare robot's voice type and lighting color during HRI on its social perception. In line with previous relevant studies, the results of the present study suggest that the voice of robots is a strong social cue that can influence people's perception of them [23,67]. The results also reveal that a robot's lighting color can affect users' social perceptions of healthcare robots. The adopted healthcare robot received higher warmth scores when it provided feedback in the form of warm lighting, and it received higher competence scores when it provided feedback in the form of cool or white lighting. The participants considered the robot to be warm and competent when it used white lighting. This result can be attributed to the properties of white light, which is colorless and associated with complex feelings, such as innocence, purity, sadness, and coldness. In the present study, high overall acceptance was discovered for the adopted healthcare robot among the participants when an adult female voice and white lighting were used, which is consistent with the results of our previous study [45]. White lighting (i.e., neutral lighting) is the most conservative choice for healthcare robots and does not easily evoke unpleasant feelings; thus, white lighting is a suitable visual feedback for robots used in any field. [PERSON] et al. [32] claimed that robots using blue (cool) lighting can attract attention. However, our findings indicate that using cool lighting for a healthcare robot can cause discomfort. Although [PERSON] et al. [68] reported that green can evoke positive emotions and red can excite people, these colors were not selected in the present study because  
Figure 4: Effects of the interaction between robot voice type and lighting color on the participants’ (**a**) feeling of warmth, (**b**) feeling of competence, (**c**) feeling of discomfort, and (**d**) overall acceptance of the robot. [PERSON] et al. [32] suggested that they should be avoided on account of the prevalence of red-green color blindness and the misreading of colors in different cultures. In addition, our previous study found that robots with children's voices are highly accepted in shopping reception, education, and companionship-related applications; however, the descriptive statistics of the present study suggest that healthcare robots with a child's voice are less suitable than are those with an adult female voice, which is in agreement with the results of [PERSON] et al. (2014) [13]. In the present study, the lighting color exhibited a moderating effect; for example, the healthcare robot was more widely accepted when it had the child voice and white lighting than when it had an adult female voice and warm lighting. The results of this study suggest that controlling verbal and visual cues not only leads to robots being favorably socially perceived but also reinforces certain aspects of social perceptions--i.e., warmth or competence--in HRI. Although many studies have discussed how the social cues of robots should be adjusted in accordance with user preferences, they have not explored the appropriate verbal cue-visual cue matching if the robot's occupation requires it to make users feel that it is highly capable or highly sociable. The results of this study suggest that to reinforce the warmth perception, an adult female voice and warm lighting can be used for robots. To ensure that users perceive a robot to be highly competent, an adult male voice and cool lighting should be employed. Studies have claimed that using an adult female voice for robots is a golden rule in robot design and development [10]; however, our previous study [22] indicated that this rule may be invalid depending on the robot's occupational role. Moreover, the results of the present study reveal that if a mismatch exists between a robot's verbal and visual cues, this golden rule is invalid.