Sometimes, a comment online is so egregious, so flagrantly wrong that you can't help but fire back. But tempting as it may be, spending hours combatting digital foes on social media won't make your thinking clearer or your prose sharper.

In fact, the longer you spend tapping out comments online, the dumber and less coherent your contributions become, according to a new study from researchers at the University of Southern California. Looking at over 40 million comments on the social media site Reddit, researchers found that users who spent more than an hour commenting tended to post shorter, less sophisticated comments that received fewer upvotes and responses.

“As your usage sessions become longer, your language becomes more elementary, less complex," Emilio Ferrara, a computer science professor and co-author of the study, said in a release. "Your content becomes less interesting, in a sense.”

The USC study looked exclusively at Reddit, but Ferrara said he hopes future research will examine other social media sites, like Facebook and Twitter, to see if sub-standard comments on those platforms might also be linked to fatigue.

Researchers only studied the length and grammatical sophistication of users' posts, so they weren't able to say whether users' comments got nastier as their sessions dragged on. That means we still don't know if posting on Reddit until 3 a.m. makes you more likely to compose the sorts of mean, spiteful comments favored by online trolls (and Microsoft's short-lived chat bot, Tay).

But, Ferrara told The Huffington Post, "that's surely something we will explore in future studies."

Whether this affects the public discourse overall is hard to tell. Emilio Ferrara, USC

The findings confirm previous studies showing that spending too much time on a single activity causes people to get worse and worse at it. Since humans can only process a certain amount of information in a given span of time, asking the brain to fire on all pistons for too long can cause people to burn out, Ferrara said.

The study also raises questions about the quality of public conversation in the U.S., both on the Internet and off. The Internet often gets blamed for destroying public debate in America. And looking at the USC study, it might be tempting to conclude that marathon commenting sessions are responsible for the sorry state of public conversation in the U.S.

But Ferrara said there's no evidence that inane or incomprehensible comments have any effect on public discourse. "Whether this affects the public discourse overall is hard to tell" Ferrara said. Ultimately, "it depends on what kind of users ... are involved in the conversation."