title: A virtual experimenter to increase standardization for the investigation of placebo effects.
abstract: Placebo effects are mediated by expectancy, which is highly influenced by psychosocial factors of a treatment context. These factors are difficult to standardize. Furthermore, dedicated placebo research often necessitates single-blind deceptive designs where biases are easily introduced. We propose a study protocol employing a virtual experimenter - a computer program designed to deliver treatment and instructions - for the purpose of standardization and reduction of biases when investigating placebo effects.
  
  
  
  To evaluate the virtual experimenter's efficacy in inducing placebo effects via expectancy manipulation, we suggest a partially blinded, deceptive design with a baseline/retest pain protocol (hand immersions in hot water bath). Between immersions, participants will receive an (actually inert) medication. Instructions pertaining to the medication will be delivered by one of three metaphors: The virtual experimenter, a human experimenter, and an audio/text presentation (predictor "Metaphor"). The second predictor includes falsely informing participants that the medication is an effective pain killer, or correctly informing them that it is, in fact, inert (predictor "Instruction"). Analysis will be performed with hierarchical linear modelling, with a sample size of N = 50. Results from two pilot studies are presented that indicate the viability of the pain protocol (N = 33), and of the virtual experimenter software and placebo manipulation (N = 48).
  
  
  
  It will be challenging to establish full comparability between all metaphors used for instruction delivery, and to account for participant differences in acceptance of their virtual interaction partner. Once established, the presence of placebo effects would suggest that the virtual experimenter exhibits sufficient cues to be perceived as a social agent. He could consequently provide a convenient platform to investigate effects of experimenter behavior, or other experimenter characteristics, e.g., sex, age, race/ethnicity or professional status. More general applications are possible, for example in psychological research such as bias research, or virtual reality research. Potential applications also exist for standardizing clinical research by documenting and communicating instructions used in clinical trials.
authors.affiliation: Department of Psychology, Clemson University, Clemson, SC, USA. bhoring@clemson.edu.
authors.forename: Bjoern
authors.initials: B
authors.lastname: Horing
authors.affiliation: Human-Centered Computing Division, School of Computing, Clemson University, Clemson, SC, USA.
authors.forename: Nathan D
authors.initials: ND
authors.lastname: Newsome
authors.affiliation: Department of Psychosomatic Medicine and Psychotherapy, University Hospital Tübingen, Tübingen, Germany.
authors.forename: Paul
authors.initials: P
authors.lastname: Enck
authors.affiliation: Human-Centered Computing Division, School of Computing, Clemson University, Clemson, SC, USA.
authors.forename: Sabarish V
authors.initials: SV
authors.lastname: Babu
authors.affiliation: Department of Psychology, Clemson University, Clemson, SC, USA.
authors.forename: Eric R
authors.initials: ER
authors.lastname: Muth
mesh_terms: D000700:Analgesics / Q000494:pharmacology; D006801:Humans; D010146:Pain; D015990:Placebo Effect; D016032:Randomized Controlled Trials as Topic / Q000379:methods / Q000592:standards*; D012015:Reference Standards; D016037:Single-Blind Method; D014584:User-Computer Interface
chemical_list: D000700:Analgesics
keywords: Bias; Blinding; Placebo analgesia; Placebo mechanisms; Standardization; Virtual reality