A is any outcome that comes from a mindset rather than from a treatment, and the idea need not stay inside pharmacology. Sleep is a good test case, because almost everybody believes a bad night costs them mentally. So 164 participants reported how they had slept, then got told a figure for their own sleep that was assigned rather than real. Did the number do anything to their performance?
The assigned figure predicted performance and the real sleep did not. Participants told they had spent 28.7 percent of the night in REM scored better on the and the Controlled Oral Word Association Task than those told 16.2 percent. Their own reported sleep quality predicted neither. Digit Span showed no effect, as the authors expected, and the Symbol Digit Modalities Test showed none either, which they did not expect.
A placebo effect is any outcome attributable to an individual’s mindset rather than to a specific treatment, and there is no reason to confine the phenomenon to pharmaceuticals. Beliefs about ordinary life should work the same way, and beliefs about sleep are a particularly good target, since nearly everyone holds a firm view about what a bad night costs them.
Two studies tested it on 164 participants. Everyone first reported their previous night’s sleep quality. They were then randomly assigned to one of two sleep quality conditions or to one of two . Those in the above-average condition were told they had spent 28.7 percent of their total sleep time in REM; those in the below-average condition were told they had spent only 16.2 percent.
Assigned sleep quality significantly predicted scores on the Paced Auditory Serial Addition Test and on the Controlled Oral Word Association Task. Self-reported sleep quality did not predict either. So the figure handed to a participant mattered and the night they had actually had did not.
The nulls are part of the result and the authors treat them honestly. Assigned sleep quality did not predict Digit Span scores, which is what they expected, and it did not predict Symbol Digit Modalities Test scores, which they did not expect. The control conditions showed the findings were not down to demand characteristics from the protocol. The conclusion they draw is that mindset can push cognitive states in both directions, on two of four measures, in a single laboratory session.
wat. A made-up percentage of REM sleep moved people’s test scores, while the sleep they actually reported having moved nothing.
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It separates how you slept from what you believe about how you slept, and only the belief moved the scores. That is worth knowing before anyone writes off a morning on the strength of a sleep tracker reading.
How do we know?
Draganich and Erdal ran two studies in which 164 participants reported their previous night’s sleep quality, then were randomly assigned to an above-average or below-average REM figure, or to one of two control conditions.
What is still unknown
Two laboratory studies with brief cognitive tasks, and the effect appeared on two tests out of four, including one null the authors call unexpected. A single session says nothing about a week of genuinely poor sleep.
Learn something?
Where to next
Does a treatment work better when it has a side effect?placebo
Does the full moon really keep people awake?sleep
What gets through while you are ignoring everyone else at a party?cognition