You've done it again: you're facing another day after too little sleep. But before you get hopped up on too much caffeine, try this quick trick for dealing with not enough rest: Tell yourself you slept well anyway. Changing your perception of the situation might be enough to boost your cognitive performance, according to research published in the Journal of Experimental Psychology: Learning, Memory and Cognition.

In the study, 164 people were divided into two groups. Everyone listened to a lecture on the importance of sleep quality and were told they'd be tested on how well they slept the previous night. They were also informed that, on average, people receive 20 percent of REM (Rapid Eye Movement) sleep every night.

The researchers then made a show of measuring each group's "brainwave frequencies," making up each person's result as they went. The people in one group were told they'd had "above average" sleep quality with 28.7 percent of that time in REM sleep, while the people in the other group learned they had "below average" sleep, with just 16.2 percent in REM sleep. This was meant to sway particpants' feelings on how well they slept.

After taking a series of cognitive tests, those who were told they scored more REM sleep fared better, while the opposite was true of the other group. It's the placebo effect in action, though the study's authors' attribute the outcome more to our expectations and how we link stimuli to outcomes.

Much like Pavlov's dogs who learned to salivate at the sound of a bell, humans have trained themselves to behave in response to their feelings. So if someone feels groggy and says she's exhausted, she'll behave that way because she believes it. "It may be that expectancy directly creates the cognitive effects from perceived sleep quality or that they are mediated by increased anxiety or decreased motivation following information about poor sleep quality," wrote the authors.

So the next time you feel half-awake, try convincing yourself otherwise to boost your performance.