Most people believe they perform worse after a sleepless night. They’re usually right. Conversely, most people think they perform better after a night of sound sleep. They’re usually right too. Now comes a third category, one that also performs well: people who slept poorly but think they slept well. The Atlantic reports on research conducted at Colorado College, where scientists asked undergrads to rate how well they had slept on a scale of one to ten. They then gave the undergrads a five-minute lesson about sleep’s effect on cognitive function, on that mentioned that adults normally spend between 20 and 25 percent of their sleep time in REM sleep, and that getting less REM sleep than that tends to cause lower performance on learning tests. They also said that those who spend more than 25 percent of their sleep time in REM sleep usually perform better on such tests. The researchers then wired up the participants and “tracked” their REM sleep, pretending to calculate that each participant got either 16.2 percent REM sleep or 28.7 percent REM sleep, and followed up with a test that measures “auditory attention and speed of processing, skills most affected by sleep deprivation.” Yes, you guessed correctly. The Atlantic reports that those undergrads who were told they had above-average REM sleep performed better on the test, and those who were told their REM sleep was below average performed worse. Read more in the Atlantic.