Introduction
In an interconnected globalized world with the ubiquitous availability of smartphones and wireless internet, online applications to improve mental health and psychological well-being are flourishing. One specific type of such intervention that has gained much attention in recent years is secular meditation practice constituting low-dose or fractional versions of prevailing mindfulness or compassion-based mental training programsRooted in contemplative traditions from Eastern cultures, a large amount of secularized mental training programs were developed over the last decades, many of which can be categorized as mindfulness or compassion-focused contemplative trainings. Most of the mindfulness-based programs are derivates of Mindfulness-Based Stress Reduction (MBSR;Apart from differences in training targets and content, contemplative practices further differ with regard to training formats. As such, they can be conducted in the form of solitary meditation, which is the case for most mindfulness programs. However, more recently, contemplative practices have also been performed in interpersonal settings, including group settings or partner-based exercises such as Insight dialoguesFurthermore, while the majority of contemplative training studies have focused on measuring training-related effects from before to after several weeks or months of training on outcomes such as neurophysiological, psychological, and other health-related markersA core aspect of phenomenological content is self-generated thought, that is, mental content and thinking patterns that are independent of the external environment or sensory stimuliBesides thought content, also phenomenology of affect and affect dynamics are crucial to mental health and psychopathologyHere, we directly compare the specific shifts in thought content as well as emotions evoked by daily 12-min app-delivered dyadic practice versus classic solitary mindfulness practice using the so-called “Cube of Thought” that assesses three dimensions of thought content, that is (1) temporality (past—future), (2) social orientation (self—other), and valence of thoughts (positive—negative) 