The Effect of Singular Nonverbal Behaviours of Experimenters on Pain Reports

Abstract

Introduction

Studies suggest facial expressions of caregivers may be important in placebo effects; however, this has not been systematically tested. This experiment investigated the effects of caregivers’ singular positive nonverbal behaviours (NBs) on pain reports.

Methods

Fifty-one males and 53 females (total of 104) participants were randomized to four groups that were displayed positive facial expressions, tone of voice, body movement, or neutral NBs of videotaped experimenters. Subjective reports of pain, stress, arousal, and cardiac activity were obtained in a pre-test, a conditioning phase, and at a post-test. Four minutes of heat pain was induced in each test, and a placebo cream was administered before the conditioning and post-test in all groups.

Results

There were no differences between the NB groups in the reduced pain. Males had larger reduction in pain in the post-test, and females had lower arousal than the opposite sex. During the conditioning, females had larger reduction in pain ie, unconditioned pain response (UPR). In females, the UPR predicted the reinforced expectation ie, increase in expectations from conditioning to post-test, and fear of minor pain negatively predicted both the UPR and reinforced expectation.

Discussion

Singular NBs of caregiver were weak to enhance placebo effects. Females had lower pain during conditioning, and the UPR amplitude in females was associated with positive expectations. Moreover, for females, fear of minor pain weakened the UPR and expectations of cream.

Conclusion

No NB of caregivers is more effective in reducing pain. Caregivers’ NBs are less effective when displayed individually. Males and females may be different in underlying mechanisms of placebo effects.

Keywords:

• placebo effects
• subtle factors
• nonverbal behaviours
• heat pain
• experimenter effects
• pain report

Data Sharing Statement

Data can be made available upon request from the corresponding author (HD).

Acknowledgments

The authors would like to thank the research assistants and actors Rosanna Matthäus, Nora Sofie Trohaug, Shunmathi Vijayaraj, Sonja Maria Mellberg, Ane Eikemo, Ingrid Endal, and Synne Ørsleie for their contribution in this study. The study protocol was previously posted as a pre-print at Researchsquare.com and published.⁵⁰

Disclosure

The authors report no conflicts of interest in this work.

Additional information

Funding

The Norwegian University of Science and Technology (NTNU), and the Bial foundation (Grant number: 36/20) funded this study.