The invention and wide use of eye tracking technology in psychological studies means we can finally re-visit that old chestnut that absolutely everyone has heard of about speaking:  make eye contact.

And apparently it’s time to re-think that old rule.

A recent study, not surprisingly, perhaps, shows that it’s not as simple as just, “Make eye contact with your audience.”  It turns out that people are less persuaded by more eye contact if they already disagree with you.  Staring at them fixedly apparently won’t sway them.

We tend to look at strangers – such as an audience member if you’re a speaker doing her best to follow the advice and make eye contact – for about three to five seconds.  One on one, we look longer – seven to ten seconds.  And in terms of percentages, we look at people something like 30 – 60 percent of the time, more when we’re listening and less when we’re talking.  If you know the person, or it’s a friendly exchange, you’ll make longer eye contact.

Those are the norms.  For normal conversational behavior.

But it gets more complicated when we’re trying to persuade someone of something.  If you’re making a relatively straightforward, simple request, then eye contact increases your persuasive power.  But if your request is subtle and will take longer, like an argument in a speech, then more eye contact doesn’t help.  And if the other person or people holds a strongly opposing view, then eye contact makes them less inclined to go along with you than if you look at them less.  Apparently more eye contact gets associated with dominance and intimidation.

So what’s the net wisdom of the research?  Don’t deploy your secret eye contact weapon when you’re talking about something controversial or when you know the audience may disagree with you.  Especially, don’t use lots of eye contact then.  Do use eye contact when the interaction is low-key, or everyone is already your friend.

Once again, the rules of conversation apply.  And who wants someone staring at them fixedly during a conversation?

But there’s also research that suggests that we tend to trust people who look at us and distrust people who don’t because we think they’re lying. And we’re right. It is a sign of lying, though a not very reliable one.  So don’t overdo it in the other direction.  Use the norms.

Is there anything more to it than that? Well, yes. There are some important subtleties. So let’s get sophisticated.

The first sophisticated rule of eye contact then is that if you’re going to make eye contact, you have to do it with your eyes wide open. Not shut, or almost shut. If the lights are bright or you’re nearsighted, that’s tough. Learn to compensate. It’s so basic to people’s reading of you that you’d be better off wearing dark glasses if you’re going to squint.

The second sophisticated rule of eye contact is that you actually have to make eye contact. With individuals. You can’t look over the heads of the group, and you can’t dart your eyes around nervously like a lizard’s tongue. Imagine you’re having a conversation with people—better yet have a conversation with individuals in the room—and look at them fixedly but not too fixedly, just as you would in a real conversation.

The third sophisticated rule of eye contact is that you should be monitoring the extent to which your colleagues are making eye contact with you. It’s a simple way to gauge their interest in what you’re saying. If 80 percent of them are focused on you, you’re OK. If 80 percent (or even 40 percent) are focused elsewhere, you’re in trouble.

Eye contact, like other aspects of human communication, can potentially convey many meanings. Make eye contact, to be sure, but be careful that you’re doing it right.

A part of this post is adapted from my new book, Power Cues:  The Subtle Science of Leading Groups, Persuading Others, and Maximizing Your Personal Impact, published May 13, 2014 by Harvard. You can order it here.