Abstract
Research shows that placebo analgesia and nocebo hyperalgesia can be induced through observational learning. Our aim was to replicate and extend these results by studying the influence of the type and colour of stimuli used as placebos on the placebo effects induced by observational learning. Three experimental and two control groups were tested. All participants received pain stimuli of the same intensity preceded by colour lights (green and red) or geometric shapes (circles and squares). Before receiving pain stimuli, participants in the experimental groups, but not in the control groups, observed a model who rated pain stimuli that were preceded by either green lights (green placebo group), red lights (red placebo group), or circles (circle placebo group) as being less painful than those preceded by either red lights (green placebo group), green lights (red placebo group), or squares (circle placebo group). As a result participants in the experimental groups rated pain stimuli preceded by either green lights (green placebo group), red lights (red placebo group), or circles (circle placebo group) as being less painful than the participants in the control groups did, indicating that placebo effect was induced. No statistically significant differences were found in the magnitudes of the placebo effects between the three experimental groups (green placebo, red placebo, and circle placebo groups), indicating that neither the type nor the colour of placebo stimuli affected the placebo effects induced by observational learning. The placebo effects induced by observational learning were found to be unrelated to the individual differences in pain anxiety, fear of pain, and empathy.
Highlights
Observational learning has been suggested as an explanatory mechanism for placebo effects [1], or as a process involved in the acquisition and modification of one of two main mechanisms that produce placebo effects, i.e., response expectancy [2]
Our study showed that there was a significantly greater difference between placebo- and nonplacebo pain ratings in participants who had observed a model rating pain stimuli preceded by placebo stimuli as significantly less painful than pain stimuli preceded by nonplacebo stimuli, even though they were receiving pain stimuli of the same intensity
We did not find any differences in the magnitudes of the placebo effects induced by observational learning when either red lights, green lights, or circles served as placebos
Summary
Observational learning has been suggested as an explanatory mechanism for placebo effects [1], or as a process involved in the acquisition and modification of one of two main mechanisms that produce placebo effects, i.e., response expectancy [2]. The latter notion is in line with Bandura’s social learning theory, which postulates that observational learning results in the acquisition and modification of expectations [3]. We can talk about the placebo effect. Type of Placebo Stimuli and Nocebo Hyperalgesia PLOS ONE | DOI:10.1371/journal.pone.0158363 June 30, 2016
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