From Ordinary to ExtraOrdinary: The Role of Placebo Effect on Intuitive Guessing

Abstract

This research examines the placebo effect on intuitive guessing within forced-choice tasks, specifically using the Zener cards test and a sound stimulus as the placebo inducer.Results from 100 naive participants demonstrated that the 'Placebo' condition achieved significantly higher correct response rates than expected by chance, with 22.3% success rate vs. 20.0% (binomial test = 2.85, p-value approximately 0.005, Cohen’s h = 0.056). Control group analyses, which included 50 participants, ruled out the possibility that these results were due to a learning effect from the order of experimental conditions.Analysis using a GLMM for binary data explored the role of experimental conditions and other variables on participant performance. The model included factors such as condition ('No-Placebo', 'Placebo', 'First Control Session', and 'Second Control Session'), participant self-reported confidence scores and reaction times, as well as reaction times in Zener card guessing tests. Among the experimental conditions, through fixed effects analysis, only the 'Placebo' one showed a significant effect (Estimate = 0.2048, p = 0.0184) with an increased likelihood of success (odds ratio = 1.227), suggesting that participants in this condition were more likely to correctly identify the Zener cards compared to the control condition. The limitations of the research are addressed in the discussion section.