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Related Experiment Videos

The placebo effect: dissolving the expectancy versus conditioning debate.

Steve Stewart-Williams1, John Podd

  • 1School of Psychology, Massey University, Palmerston North, New Zealand. s.j.stewart-williams@massey.ac.nz

Psychological Bulletin
|February 26, 2004
PubMed
Summary

This review clarifies placebo effect models, distinguishing shaping factors from learning mechanisms. It suggests both conditioning and verbal information influence placebo responses, sometimes bypassing conscious awareness.

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Area of Science:

  • Psychology
  • Neuroscience
  • Medical Humanities

Background:

  • The placebo effect is a complex phenomenon with two primary theoretical models: expectancy theory and classical conditioning.
  • A long-standing theoretical impasse exists regarding the precise mechanisms underlying placebo effects.
  • Distinguishing between factors that shape placebo effects and the learning processes that mediate them is crucial.

Purpose of the Study:

  • To review the existing literature on expectancy theory and classical conditioning models of the placebo effect.
  • To propose a framework for resolving theoretical disputes surrounding the placebo effect.
  • To differentiate between factors influencing placebo responses and the learning mechanisms involved.

Main Methods:

  • Literature review of studies on placebo effect models.

Related Experiment Videos

  • Analysis of research differentiating between shaping factors and mediating learning processes.
  • Examination of the role of conditioning and verbal information in placebo responses.

    • Main Results:

    • Classical conditioning procedures are identified as a significant factor shaping placebo effects.
    • Verbal information is also demonstrated to influence placebo effects.
    • Both conditioning and information can shape conscious expectancies, which mediate some placebo effects.
    • Evidence suggests conditioning can also induce placebo effects independent of conscious cognition.

    Conclusions:

    • A clear distinction between shaping factors and mediating learning is essential for understanding the placebo effect.
    • Placebo effects are influenced by multiple factors, including conditioning and informational input.
    • The mechanisms of the placebo effect involve both conscious expectancies and potentially non-conscious processes.