How mindfulness training promotes positive emotions: Dismantling acceptance skills training in two randomized controlled trials

Mindfulness meditation interventions – which train skills in monitoring present-moment experiences with a lens of acceptance – have shown promise for increasing positive emotions. Using a theory-based approach, we hypothesized that learning acceptance skills in mindfulness interventions helps people notice more positive experiences in daily life, and tested whether removing acceptance training from mindfulness interventions would eliminate intervention- related boosts in positive affect. In two randomized controlled trials (RCTs) of stressed community adults, mindfulness skills were dismantled into two structurally equivalent interventions: (1) training in both monitoring and acceptance (Monitor+Accept) and (2) training in monitoring only (Monitor Only) without acceptance training. Study 1 tested 8-week group- based Monitor+Accept and Monitor Only interventions compared to a no treatment control group. Study 2 tested 2-week smartphone-based Monitor+Accept and Monitor Only interventions compared to an active control training. In both studies, end-of-day and momentary positive affect and negative affect were measured in daily life for three days pre- and post- intervention using ambulatory assessments. As predicted, across two RCTs, Monitor+Accept training increased positive affect compared to both Monitor Only and control groups. In Study 1, this effect was observed in end-of-day positive affect. In Study 2, this effect was found in both end-of-day and momentary positive affect outcomes. In contrast, all active interventions in Studies 1 and 2 decreased negative affect. These studies provide the first experimental evidence that developing an orientation of acceptance toward present-moment experiences is a central mechanism of mindfulness interventions for boosting positive emotions in daily life.