Post-intervention debriefing
After completing the study (and before being unblinded), participants were asked whether they thought they received real or control intervention during the neurofeedback sessions and how confident they were with the guess (on a scale of 1 to 10). Debriefing data from these two items were converted to an intervention belief variable by multiplying the guessed group (1 for real and −1 for sham) by level of confidence (1 to 10). This variable was included as a covariate in the follow-up analyses of covariance (ANCOVAs) on the outcome measures.