One of us or one of them? The effects of the model's and observer's characteristics on placebo analgesia induced by observational learning

Abstract

Previous studies have proved that observational learning can induce placebo analgesia, but the factors that influence observationally induced placebo analgesia have not yet been extensively examined. The primary goal of this study was to investigate the effect of information about the role that the observed person (model) plays in the experiment on the magnitude of the observationally induced placebo effect. This study also examined the contribution of the observer's empathy, conformity and fear of pain to the placebo analgesia induced by observational learning. The effects induced in two experimental groups and one control group were compared. Participants in the experimental groups observed a model introduced as either another participant taking part in the study or a coworker of the experimenter. The model rated the intensity of pain induced by electrocutaneous stimuli preceded by color stimuli. One-half of all participants watched a model rating pain stimuli preceded by the color orange as higher than stimuli preceded by the color blue; for the other half, the ratings were the opposite. There was no observation in the control group. Subsequently, all participants received pain stimuli of the same intensity preceded by orange and blue stimuli and rated the intensity of the experienced pain. Placebo analgesia was found in both experimental groups. However, the way the observed model was introduced to participants did not affect the magnitude of placebo analgesia. Thus, the study showed that the role played by the model is not crucial for observationally induced placebo analgesia. The examined observer's individual characteristics did not predict the magnitude of placebo effect.

Fig 1. Study design.

The study consisted of two experimental groups (co-participant group and demonstrator group) and one control group. In the co-participant and demonstrator groups, participants observed a model (presented to the participants as another person taking part in the study or as a coworker of the experimenter, respectively) who rated electrocutaneous stimuli preceded by one of the colors as less painful than those preceded by the other. In the control group, there was no observation phase. In the testing phase, all subjects received 16 pain stimuli of the same individually adjusted intensity.

Fig 2

Pain ratings during the testing phase in co-participant group (A), demonstrator group (B) and control group (C). The figure depicts mean pain intensity ratings for stimuli preceded by color_LOW (i.e. the color preceding pain stimuli rated by the model as less painful) and color_HIGH (i.e. the color preceding stimuli rated by the model as more painful) in two experimental groups and preceded by color₁ (i.e. blue or orange) and color₂ (i.e. orange or blue) in the control group. Abbreviations: NRS–Numeric Rating Scale; SEM–Standard Error of the Mean.

Fig 3. The magnitude of placebo analgesia.

The figure depicts differences in pain intensity ratings between the co-participant group, demonstrator group and control group. Abbreviations: NRS–Numeric Rating Scale; SEM–Standard Error of the Mean.