A pilot randomized controlled trial published in the Journal of Clinical Psychology found that explicitly inducing positive expectations before a mindfulness body scan changed how much the exercise helped, and the direction of that change depended on what participants expected going in. Researchers led by Stefan Salzmann of Marburg University, with coauthors Frank Euteneuer, Christiane Melzig, Winfried Rief and Christoph Benke, randomized 66 healthy adults in a 1:1:1 design to a body scan with an expectation-boosting instruction, a body scan with a neutral instruction, or a neutral audiobook with no mindfulness content.
On the trial's primary measure, change in positive affect, the expectation-boosted group differed from both comparison groups (group effect p = 0.018, d = 0.65; versus the neutral body-scan group, p = 0.015, d = -0.77; versus the audiobook group, p = 0.012, d = -0.80). The more striking result came from a planned moderator analysis: participants who entered the study with low baseline expectations for the mindfulness exercise showed the largest gains after the expectation-boosting instruction, including bigger increases in reported treatment expectations and mindfulness and a larger drop in perceived stress, compared with the other two groups.
The effect ran the other way for participants who already expected the exercise to help. In that group, adding the positive-expectation instruction produced less stress reduction than the neutral-instruction version of the same body scan, a pattern the authors describe as consistent with an expectation violation effect rather than an added benefit. No significant main effects on other secondary outcomes were reported in the abstract.