Did your Facebook News Feed seem a little too happy, or perhaps a little too depressing, for one week in January 2012? That may have been because researchers were experimenting with your News Feed to figure out more about how humans’ emotions work when we’re physically apart.

By tweaking the Facebook News Feed algorithm and studying nearly 700,000 Facebook users’ posts, Facebook’s data scientists and researchers found that emotional states can be transmitted between people without face-to-face interaction, according to a study published earlier this month.

For the study, published in the Proceedings of the National Academy of Sciences, researchers analyzed over 3 million posts containing over 122 million words and used an algorithm to characterize the language as positive or negative. Facebook’s data team then adjusted the amount of positive or negative Facebook language users were exposed to on their News Feeds to see how they would react.

Researchers Adam Kramer, of Facebook; Jamie Guillory, of the University of California, San Francisco; and Jeffrey Hancock, of Cornell University, found that when users were exposed to fewer positive posts, they would themselves produce fewer positive posts and more negative posts. The reverse was true when they were exposed to fewer negative posts. In other words, verbal and textual cues have a big impact on our emotions, even if we don’t hear a person’s tone of voice or see their body language.

“These results suggest that the emotions expressed by friends, via online social networks, influence our own moods,” said the team in the study.

The data was analyzed by computers, so it’s not like a scientist was poring over your Facebook posts. And if you feel weirded out about Facebook looking at your posts without your consent — well, you’ve already given your consent. You just haven’t read Facebook’s privacy policy, which gives the company permission to carry out studies like these.

In any case, the next time you feel your mood changing while you’re on Facebook, it might have something to do with what your friends are posting.

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