You can’t spell Twitter without an “i”—or tweet, it seems, without a me, my or mine.

Everyone already knows that social media is a great place for narcissists. The news: our mobile phones might be enabling our egos. A new study just published in the Journal of Communication finds that tweets sent from smartphones are 25% more negative than tweets sent from computers. “Have they had a bad sandwich? Have they been stuck in bad traffic? They want to talk about it,” says study author Dhiraj Murthy, who has been studying Twitter since the social network’s start. And we do talk about it, ad nauseam.

Tweets from phones were also more egotistical. “That was a very surprising finding,” says Murthy. “That speaks volumes to me.”

To come to these conclusions, Murthy, at Goldsmiths, University of London, and his colleagues collected 235 million tweets sent from North America over six weeks in 2013. They then borrowed a tactic from social psychology to look at certain word associations in the messages by using the Implicit Association Test, a kind of personality test based on word analysis.

Some words, including my, me, mine and self, have been associated with egocentricity, while others, like pain, grief and agony, have been linked, no surprise, to negativity. The researchers also looked at the times of day people tweeted and whether they were sending messages from a mobile phone or computer.

MORE: Your Phone Knows If You’re Depressed With 87% Accuracy

Our tweets are most negative and egocentric during certain days of the week and certain times of the day.

Tweets are the most negative in the early morning and the late evening. And while our ego chills out a bit during the workday, it rises right after, our tweets reveal. “We leave work, we leave school and we start becoming more egocentric,” Murthy says. Happily, though, we seem to give our narcissism the weekends off. Sunday morning, the ego’s holy day of rest, is the time we tweet our least egocentric thoughts.

Twitter provides a documented stream of consciousness of our thoughts, and our phones don’t even require us to wait until we get back to our computer to let the world (and the world’s Twitter researchers) know exactly what we’re thinking. “Because everything has become more mobile, it’s reflecting more of what we’re doing in the moment,” Murthy says. “Some of the thoughts we had before that we weren’t communicating are now coming through our mobile devices, and there’s a certain egocentric bias emerging from it.”

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Write to Mandy Oaklander at mandy.oaklander@time.com.