In my last article I discussed research that put the “sleep debt” theory to the test. In some ways the theory held up – catch-up sleep helped ward off daytime sleepiness and reduced tissue inflammation. What catch-up sleep did not do is return attention levels back to what they were before a few days of sleep deprivation. Mental focus took a hit that paying back the sleep debt couldn’t reverse.
In another recent study researchers wanted to find out if our mental performance can be improved by merely believing we’ve slept more than we actually have.
Researchers polled a group of 50 participants on how well they’d slept the previous night. They were then hooked up to machines that, they were told, measured their brain waves, pulse and heart-rate, and would be able to assess the true quality of their sleep. This was actually a trick the researchers used to make half of the participants think they received 16.2 % REM sleep the previous night (well below average), and the other half believe they received 28.7 % REM sleep (well above average).
Participants were then asked to complete a set of difficult math questions. Those told they received below-average REM sleep scored an average of 22 points on the test – significantly worse than participants told they received above-average REM sleep (who scored almost 35 points, on average).
A follow-up study used the same trickery, but this time asked participants to complete a few different sorts of tests: a math test, a word-choice test, a task designed to measure visual-motor processing speed, and another designed to test short-term memory. The follow-up also improved on the first study by adding two control groups that completed the tests but were not tricked into thinking they’d slept well or poorly.
Believing they’d slept well did not improve participants’ performance on the visual-motor or memory tasks. But–for both the math and word-choice tests–perceived sleep quality correlated with performance. In fact, participants told they’d slept well not only outperformed the other groups on the word-choice test, they also performed well above the average score on the test for anyone taking it.
What these results suggest (especially those from the follow-up study) is that believing we’ve slept well makes a big difference in mental performance.
Knowing that helps me understand the marketing appeal of the black band I’m wearing on my right wrist. It’s called the UP 24, made by Jawbone, and it’s one of several items on the market that use your smartphone to track, among other things, the quality of your sleep.
In a future article I’m going to report more on the $150 band I’m wearing, and its counterparts, and let you know if they’re worth the investment. Until then, keep counting your sheep.
The study was published in the Journal of Experimental Psychology: Learning, Memory and Cognition.
You can find David DiSalvo on Twitter @neuronarrative and at his website, The Daily Brain. His latest book is Brain Changer: How Harnessing Your Brain’s Power To Adapt Can Change Your Life.
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