The Influence of Robot Facial Expression and Inclusion Behavior on Rapport and Trust in Older Adults: Mixed-Factorial Experimental Study

Background: The World Health Organization framework for healthy aging emphasizes that the capacity to establish and sustain relationships is a vital component of functional ability. Social robots offer valuable support for this relational aspect, although their effectiveness is contingent upon the quality of the interactions. While it is established that facial expressions and inclusive behaviors can influence rapport building, the combined effects of these elements on older adults remain unexamined. Objective: This study aimed to investigate the main and interaction effects of robot facial expression (happy vs unhappy) and interaction style (inclusive vs exclusive) on the development of rapport between social robots and older adults residing in the community. Methods: A 2 × 2 mixed-factorial experimental design was used in this study, involving 53 community-dwelling older adults (mean age 70.57, SD 4.27 years; n=45, 84.9% female). Participants engaged in a gamified interaction known as Radish Squat featuring 2 humanoid robots that exhibited various combinations of facial expressions and interaction styles. The inclusive robot designated participants within the game 75% of the time, whereas the exclusive robot did so approximately 25% of the time. Dependent measures included robot acceptance, rapport, rapport expectation, and trust. Behavioral designation frequencies were recorded throughout the gameplay. A mixed-design repeated-measure ANOVA was conducted to examine both main and interaction effects. Results: Facial expression exhibited significant main effects on acceptance (F1,51=14.27; P