Two is better than one: Apologies from two robots are preferred.

Although the capabilities of service robots are increasing, avoiding any mistakes is difficult. Therefore, strategies for mitigating mistakes, such as apology behavior designs, are essential for service robots. Past studies reported that costly apology is perceived as more sincere than non-costly ones and more acceptable. To increase the apology cost in robot service situations, we thought that using multiple robots would increase the perceived costs in the of financial, physical, and time costs. Therefore, we focused on the number of robots who apologize for their mistakes as well as their individual, specific roles and behaviors during such apologies. We investigated the differences in perceived impressions toward apologies from two robots (the main robot that makes a mistake and apologizes and a sub-robot that also apologizes) and an apology from just one robot (only the main robot) through a web survey with 168 valid participants. The experiment results showed that the participants significantly preferred and positively evaluated apologies from two robots more than one robot in the context of forgiveness, negative word-of-mouth, trust, and intention to use. We also conducted another web survey with 430 valid participants to investigate the effects of different roles for the sub-robot: apologize-only, cleaning-up-only, and both actions. The experimental results showed that the participants significantly preferred and positively evaluated both actions in the context of forgiveness and reliable/competent perspectives.