UPDATE: Unethical Facebook Emotional Contagion Study Not Funded By The Army, Happens All The Time.

Psychologists have known for a long time that emotions are contagious. If you hang out with someone who’s feeling shitty, you might end up feeling shitty too. Pretty basic. But now researchers have found that the emotions you see people express online can be just as contagious. New Scientist reports:

A team of researchers, led by Adam Kramer at Facebook in Menlo Park, California, was curious to see if this phenomenon would occur online. To find out, they manipulated which posts showed up on the news feeds of more than 600,000 Facebook users. For one week, some users saw fewer posts with negative emotional words than usual, while others saw fewer posts with positive ones.

Apparently what many of us feared is already a reality: Facebook is using us as lab rats, and not just to figure out which ads we’ll respond to but to actually change our emotions. According to the authors of this study, it was all perfectly legal. Using an algorithm that can recognize negative or positive words, the researchers were able to comb through NewsFeeds without actually viewing any text that may have been protected under users’ privacy settings. “As such, it was consistent with Facebook’s Data Use Policy, to which all users agree prior to creating an account on Facebook, constituting informed consent for this research,” the study’s authors wrote. That’s right: You consented to be randomly selected for this kind of research when you signed up for Facebook. Might want to check out that User Policy again.

With that out of the way, the results of their tests predictably proved that people are emotionally suggestible online, though not as much as offline.

People were more likely to use positive words in Facebook posts if they had been exposed to fewer negative posts throughout the week, and vice versa. The effect was significant, though modest.

If this study is taken seriously, it could have an affect on how people see online harassment, which is still seen as less damaging than abuse in “real life.” This research also provides further motivation to avoid getting caught up in online arguments that get you down — those angry feelings aren’t going to disappear when you shut off your computer.