Objective: We sought to address a growing debate regarding the adverse and salutary impact of unusual, extraordinary, or intense subjective experiences during mindfulness interventions. To do so, we empirically characterized such peak experiences during an intensive mindfulness meditation intervention and their impact post-intervention. Method: We conducted a preregistered prospective intervention study among 96 adults who registered to a six-day mindfulness meditation retreat and 47 matched-controls. Controls were selected from a pool of 487 people recruited from the same community of meditators as retreat participants and systematically matched to retreat group on age and lifetime meditation experience. Measures included the Peak Meditative Experience Scale (PMES) and the Impact of PMES (I-PMES). Results: Seventeen peak experiences that were predominantly pleasant (e.g., deep and unusual peace, aha! moment) occurred more frequently among retreat participants than among matched-controls in daily living (ps < .05; mean φ = .33). In contrast, 14 peak experiences that were mostly unpleasant (e.g., flashbacks, overwhelming sadness) occurred at similar rates in both groups (ps > .05). At two-week follow-up, the perceived impact of all pleasant and most unpleasant peak experiences was more salutary than adverse (ps ≤ .015; M Cohen’s d = 1.61). Conclusions: Peak experiences that resulted from intensive mindfulness meditation training were primarily pleasant and had a large salutary impact post-retreat. Inconsistent with conclusions from uncontrolled studies, findings document that intensive mindfulness meditation training may not contribute to unpleasant peak experiences, and even when they occurred their impact was typically more salutary than adverse.

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Although attention is thought to have a definitive role in mindfulness meditation training and its salutary mechanisms of action, extant empirical evidence from more than two decades of research does not strongly support this central theoretical premise. We argue that the discrepancy between compelling theory and extant data is, in large part, explained by the field’s empirical focus on attention to external stimuli (e.g., visual) rather than attention to internal experience (e.g., bodily sensations, thoughts) that mindfulness training targets. To account for these findings, as well as to advance field-wide understanding of mindfulnesss mechanisms of action, we propose the Mindfulness Internal Attention (MIA) framework. We theorize that mindfulness meditation training mainly targets internal attentional processes. Moreover, we theorize that the effects of mindfulness training on internal attention generalize to late-stage external attentional processes that operate on abstracted representations of external information and share cognitive resources with internal attention. In contrast, we theorize that the effects of mindfulness training on internal attention will not generalize to early-stage external attentional processes that operate on sensory-perceptual information. We report a critical review of empirical findings that support these central tenets of the MIA framework. Finally, to advance research on mindfulness training and attention, we propose future directions related to the integration of emerging measures of internal attention into mindfulness research, study of shared resources between external and internal attention in mindfulness training, and study of internal attention processes as mechanisms of mindfulness training.