Indiana University-Purdue University Indianapolis (IUPUI) / Placebo has been found to be an important component of treatments including psychological and pharmacological treatment of depression, transplant surgery for Parkinson’s, acupuncture, smoking cessation interventions, and analgesic treatment of pain. Although the placebo effect has been observed across a wide range of disciplines, the effect sizes vary widely and it is not well understood how placebo effects are produced. The current study draws upon research in perception and motivation to propose a more comprehensive model of the placebo effect. Specifically, the model proposes that more motivated persons pay greater attention to bodily sensations and other stimuli, which are then interpreted according to expectations, producing a placebo response. In the current study, both motivation and outcome expectancy were manipulated, creating a 2x2 study design. College students (N=152) were asked to evaluate a series of placebo pheromone substances (slightly scented water) and attention/task diligence was assessed as the amount of time spent on the rating task and the number of evaluations made. The placebo response was assessed as the attractiveness rating of the chosen sample and the variability in ratings, with greater variability and higher attractiveness ratings indicating greater placebo response. It was predicted that those in the high motivation group would have greater diligence on the rating task, which would, in turn, lead to greater placebo response. It was further predicted that there would be a main effect for expectancy on placebo response. Consistent with hypothesized effects, more highly motivated students had greater placebo responses, and the relationship was mediated by task diligence. Thus, as students spent greater time on the evaluation task, they found the scent of their chosen sample to be more pleasing and perceived greater differences among samples. No effect was found for expectancy. These findings are important because they suggest possible mechanisms for maximizing treatment effects in medical and psychological settings, where factors such as nonspecific treatment effects and placebo are believed to influence outcomes. Future research should seek to further clarify the relationship of expectancy and motivation to placebo outcomes by examining mediating factors such as attention and carefully manipulating both variables to ensure maximum effects.

People have always been fascinated by the extent to which belief or will may influence<p>behavior. Proverbs, like “we tend to get what we expect,” and concepts, such as optimistic<p>thinking or self-fulfilling prophecy, reflect this intuition of an important link between one’s<p>dispositions and subsequent behavior. In other words, one’s predictions directly or<p>indirectly cause them to become true. In a similar manner, every culture, country or<p>religion has their own words for ‘expectation,’ ‘belief,’ ‘disappointment,’ ‘surprise,’ and<p>generally all have the same meaning: under uncertainty, what one expects or believes is the<p>most likely to happen. This relation between what caused a reaction in the past will<p>probably cause it again in the future might not be realistic. If the expected outcome is not<p>confirmed, it may result in a personal ‘disappointment’, and if the outcome fits no<p>expectations, it will be a ‘surprise’. Our brain is hardwired with this heuristic capacity of<p>learning the cause-effect relationship and to project its probability as the basis for much of<p>our behavior, as well as cognitions. This experience-based expectation is a form of<p>learning that helps the brain to bypass an exhaustive search in finding a satisfactory<p>solution. Expectations may thus be considered an innate theory of causality; that is, a set of<p>factors (causes) generating a given phenomenon (effects) influence the way we treat<p>incoming information but also the way we retrieve the stored information. These<p>expectancy templates may well represent one of the basic rules of how the brain processes<p>information, affecting the way we perceive the world, direct our attention and deal with<p>conflicting information. In fact, expectations have been shown to influence our judgments<p>and social interactions, along with our volition to individually decide and commit to a<p>particular course of action. However, people’s expectations may elicit the anticipation of<p>their own automatic reactions to various situations and behaviors cues, and can explain that<p>expecting to feel an increase in alertness after coffee consumption leads to experiencing<p>the consequent physiologic and behavioral states. We call this behavior-response<p>expectancy. This non-volitional form of expectation has been shown to influence<p>cognitions such as memory, pain, visual awareness, implicit learning and attention, through<p>the mediation of phenomena like placebo effects and hypnotic behaviors. Importantly,when talking about expectations, placebo and hypnosis, it is important to note that we are<p>also talking about suggestion and its modulating capability. In other words, suggestion has<p>the power to create response expectancies that activate automatic responses, which will, in<p>turn, influence cognition and behavior so as to shape them congruently with the expected<p>outcome. Accordingly, hypnotic inductions are a systematic manipulation of expectancy,<p>similar to placebo, and therefore they both work in a similar way. Considering such<p>assumptions, the major question we address in this PhD thesis is to know if these<p>expectancy-based mechanisms are capable of modulating more high-level information<p>processing such as cognitive conflict resolution, as is present in the well-known Stroop<p>task. In fact, in a recent series of studies, reduction or elimination of Stroop congruency<p>effects was obtained through suggestion and hypnotic induction. In this PhD thesis, it is<p>asked whether a suggestion reinforced by placebos, operating through response-expectancy<p>mechanisms, is able to induce a top-down cognitive modulation to overcome cognitive<p>conflict in the Stroop task, similar to those results found using suggestion and hypnosis<p>manipulation. / Doctorat en Sciences Psychologiques et de l'éducation / info:eu-repo/semantics/nonPublished