The impact of encouraging utterances by a human partner and a conversational robot on older adults' subjective well-being: a 6-week sustained interaction.

INTRODUCTION: In human-human communication, encouragement has been closely associated with subjective well-being (SWB). However, the long-term effects of encouragement in human-robot interaction remain unclear, particularly in comparison with human-delivered encouragement and across different encouragement strategy types. SWB comprises both affective well-being (AWB) and cognitive well-being (CWB). This study investigated whether sustained verbal encouragement from a human partner and a conversational robot could enhance older adults' SWB.

METHODS: A two-phase design was adopted. First, a preliminary online survey with 55 older Japanese adults (aged 65-74) was conducted to select encouragement strategies for the main experiment, identifying offering specific actions (high-efficacy) and distraction (low-efficacy) as two encouragement strategies that differed significantly in participants' perceived effectiveness (p < 0.05). Based on this survey, 18 older Japanese adults (aged 62-90) were recruited for an exploratory 6-week longitudinal experiment. Participants interacted with either a human partner or a conversational robot once per week and were randomly assigned to one of four conditions: human partner or social robot (RoBoHoN) crossed with high- or low-perceived-efficacy encouragement strategy. SWB was assessed using questionnaires, while post-session open-ended responses, diary entries, and post-experiment interviews provided qualitative data on encouragement experience, perceived SWB changes, and participants' perceived sources of SWB change.

RESULTS: Results suggested that high-efficacy verbal encouragement may positively influence older adults' SWB, possibly with a stronger effect than low-efficacy encouragement, with a crossover-like pattern emerging: for AWB, the advantage of high-efficacy over low-efficacy encouragement tended to be more pronounced in the robot condition (Δ gap = 2.8) than the human condition (Δ gap = 0.5), whereas for CWB, it appeared to be more pronounced in the human condition (Δ gap = 2.0) than the robot condition (Δ gap = 0.2); these crossover trends should be interpreted with caution given the small sample size. Qualitative findings further suggested that the conversation itself may have contributed to participants' perceived emotional support in the Japanese cultural context.

DISCUSSION: These preliminary longitudinal findings suggest that social robots and human partners may both contribute to supporting older adults' SWB and may play complementary roles.