Here's the science behind why it's so hard to maintain eye contact when you're talking to someone

Why do you glance off to the side when you speak? It's like you're trying to pull a word out of some blank space in the distance.

Breaking eye contact mid-sentence is a strange habit, but almost everyone seems to do it every once in a while.

And a pair of researchers at Kyoto University in Japan offer an intriguing answer as to why in a new study, which will be published in the journal Cognition.

They suggest that maintaining eye contact requires a level of mental effort and uses up your brain's resources.

So sometimes, when you speak, the tasks of coming up with the next word and maintaining eye contact become too much for your brain to handle. Then - snap - your attention shifts to the middle distance, and all the extra oomph in your head goes toward picking your next word.

Here's how the researchers came to their conclusions.

We know from a previous study that different word-associations are more or less hard to come up with. And there's different reasons you might take time to come up with a word.

Some word association tasks are hard because there are too many options. That means the mechanism in your mind for picking a word has to run longer, but it doesn't tax your conscious thought.

For example: Try to come up with a verb for the word scissors.

Now come up with a verb for the word ball.

Typically people think of a word faster for scissors, because there's only really one good option: cut.

But if you have a ball you can kick it, throw it, catch it, or play with it.

And then there are the word associations that don't overwhelm you with choice anxiety, but have weak enough connections that you have to consciously think about them to pick a verb.

So if you're given the word car, it's not too hard to get to drive, so you probably don't have to think about it. But if the word is leaf, you might have to mull it over a bit before getting to fall.

For the eye contact study, the researchers had 26 participants play the word association game while making eye contact with a computer-generated face.

They found that eye contact did make it harder to think of words, so the participants would take longer to think of them. But the effect was only significant when trying to make weak connections, like that between leaf and fall ;- the sort that require conscious thought to come up with.

That means eye contact doesn't directly interfere with the mental task of picking words. But it takes some cognitive effort to maintain. So when you're speaking and you come to a word you have to actively think to come up with, the two tasks come into conflict.

And then, perhaps, you might glance away.