Procedure
OLP
The study followed a single-blind, between-subjects design with two sessions (Baseline and Test; see also Fig. Overview of the study design. First, all tasks were completed before participants completed the questionnaires. Tests and questionnaires were then completed in German and in a randomized order, except the d2 which was administered first and the learning task which was always administered last. Trait questionnaires/tasks were only administered at the Baseline (*), all state measures were acquired twice. Each box either contained 45 placebo pills (Zeebo Relief from Zeebo Effect, LCC; white-blue pills filled with silicon dioxide, titanium dioxide and microcrystalline cellulose) in their original packaging (OLP group), or filler material of similar weight but no pills (CTR group). Both groups also received a note that stated the group they had been allocated to, OLP intake instructions (OLP group) or the instructions to do nothing (CTR group) and a question asking about their satisfaction with the group assignment. We chose this approach to control for test–retest training effects over time. The OLP group was fully informed that the pills were placebos and instructed to take one tablet twice daily for 21 days, starting with the day after the Baseline session. This procedure and duration of the OLP intervention had been successfully established in previous work