The placebo effect is a beneficial outcome resulting from a person's anticipation that an intervention is likely to help them. Whatever increases the expectation of benefit can act as a placebo, from sugar pills to subtle verbal suggestion. We usually think of placebos in the context of medical treatment, but the placebo effect is seen across a range of non-medical interventions, including psychotherapy and mindfulness meditation. The placebo effect may or may not be the result of intentional deception. A provider’s obvious enthusiasm for a particular procedure or practice might do the trick.

The placebo effect has also been found in interventions designed to improve cognitive functioning in areas such as intelligence, attention, memory, and self-control. For instance, researchers in one study produced two flyers to recruit subjects. One flyer set up high expectations of cognitive improvement and the other didn’t. Subjects subsequently underwent the same training but only those who had responded to the suggestive flyer actually showed improvement: the equivalent of a 5-10 point increase on a standard intelligence test.

Other researchers looked at what enhances the placebo effect in cognitive training - that is, what increases expectation of benefit. They found that study participants who reported training as more challenging expected greater benefit and performed better on post-training cognitive tests than subjects who reported training as less challenging. In other words, the experience of mental effort increased these subjects’ expectations of cognitive gain.

Which brings me to the subject of control groups. Researchers have to control for the placebo effect to figure out why a particular intervention is or is not effective. That means research on interventions must include an “active” control group with similar expectations of similar kinds of benefit as the main “treatment” group. In the case of cognitive training, that means the control group will have to engage in some kind of mental labor, not just watch videos or listen to lectures. No, they need to do something that makes them believe what they’re doing may improve their cognitive skills. Unfortunately, few cognitive training studies include active control groups and fewer still control for expectations of benefit.


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