'They took 164 participants and explained brain science and sleep and told these participants REM sleep will improve your brain performance.'
The participants were then asked to rate the prior night's sleep from 1 to 10.
Then, as The Telegraph reports, the researchers told students a new machine could measure the quality of their sleep from the night before by measuring their pulse, heart rate and brainwave frequency.
But this machine doesn't actually work - they made it all up. All participants were hooked up to the fake machine and then separated into two groups.
'The ones that were told they had more REM sleep did better on tests of performance, despite how they thought they slept the night before,' CBS explains.
But can simply repeating to yourself over and over that you had great sleep really be the key to feeling rested?
One researcher told Popular Science that the answer is ... maybe. He said that if 'you're able to convince yourself that your bedtime routine is working - whether it's reading, exercising, or eating honey - you might see the cognitive benefits of improved sleep even on nights when you don't actually sleep better.'
And if you aren't so convinced, hitting the hay a little earlier can also do the trick.