In the beginning, the technology gods created the Internet and saw that it was good. Here, at last, was a public sphere with unlimited potential for reasoned debate and the thoughtful exchange of ideas, an enlightening conversational bridge across the many geographic, social, cultural, ideological and economic boundaries that ordinarily separate us in life, a way to pay bills without a stamp.

Then someone invented "reader comments" and paradise was lost.

The Web, it should be said, is still a marvelous place for public debate. But when it comes to reading and understanding news stories online - like this one, for example - the medium can have a surprisingly potent effect on the message. Comments from some readers, our research shows, can significantly distort what other readers think was reported in the first place.

But here, it's not the content of the comments that matters. It's the tone.

In a study published online last month in The Journal of Computer-Mediated Communication, we and three colleagues report on an experiment designed to measure what one might call "the nasty effect."

We asked 1,183 participants to carefully read a news post on a fictitious blog, explaining the potential risks and benefits of a new technology product called nanosilver. These infinitesimal silver particles, tinier than 100-billionths of a meter in any dimension, have several potential benefits (like antibacterial properties) and risks (like water contamination), the online article reported.

Then we had participants read comments on the post, supposedly from other readers, and respond to questions regarding the content of the article itself.

Half of our sample was exposed to civil reader comments and the other half to rude ones - though the actual content, length and intensity of the comments, which varied from being supportive of the new technology to being wary of the risks, were consistent across both groups. The only difference was that the rude ones contained epithets or curse words, as in: "If you don't see the benefits of using nanotechnology in these kinds of products, you're an idiot" and "You're stupid if you're not thinking of the risks for the fish and other plants and animals in water tainted with silver."

The results were both surprising and disturbing. Uncivil comments not only polarized readers, but they often changed a participant's interpretation of the news story itself.

In the civil group, those who initially did or did not support the technology - whom we identified with preliminary survey questions - continued to feel the same way after reading the comments. Those exposed to rude comments, however, ended up with a much more polarized understanding of the risks connected with the technology.

Simply including an ad hominem attack in a reader comment was enough to make study participants think the downside of the reported technology was greater than they'd previously thought.

While it's hard to quantify the distortional effects of such online nastiness, it's bound to be quite substantial, particularly - and perhaps ironically - in the area of science news.

An estimated 60 percent of the Americans seeking information about specific scientific matters say the Internet is their primary source of information - ranking it higher than any other news source.

Our emerging online media landscape has created a new public forum without the traditional social norms and self-regulation that typically govern our in-person exchanges - and that medium, increasingly, shapes both what we know and what we think we know.

One possible approach to moderate the nasty effect, of course, is to shut down online reader comments altogether, as some media organizations and bloggers have done. Paul Krugman's blog post on this newspaper's Web site on the 10th anniversary of Sept. 11, for instance, simply ended with "I'm not going to allow comments on this post, for obvious reasons."

Other media outlets have devised rules to promote civility or have actively moderated reader comments.

But as they say, the genie is out of the bottle. Reader interaction is part of what makes the Web the Web - and, for that matter, Facebook, Twitter and every other social media platform what they are. This phenomenon will only gain momentum as we move deeper into a world of smart TVs and mobile devices where any type of content is immediately embedded in a constant stream of social context and commentary.

It's possible that the social norms in this brave new domain will change once more - with users shunning meanspirited attacks from posters hiding behind pseudonyms and cultivating civil debate instead.

Until then, beware the nasty effect.