You may not have noticed, but you spend about ten per cent of the time you’re awake with your eyes closed. I’m talking about the fact you blink your eyes every few seconds. Why do we blink so often and why don’t we notice the world plunge into darkness every time we do?

Don’t be afraid to blink; you won’t miss anything! Image credit Randy Wick via Flickr

Be clean, eyeball

If you’re awake for 16 hours a day, you have your eyes closed for more than an hour and a half each day. That seems a lot and suggests blinking must be doing something important. The most obvious explanation for blinking is the fact a blink clears away any pesky dust particles that might have landed on your eye. Blinking also keeps your eyeball moist. Each blink lasts only a fraction of a second, but that’s enough time to spread the perfect mix of lubricating fluids across the surface of your eye. Is it as simple as that? Yes, and no.

The act of blinking does keep our eyes clean and lubricated, but research has shown we wouldn’t need to blink nearly so often if that were the main game. Think about the last time you had a staring competition: you were easily able to stop blinking for far longer than a few seconds. There’s more going on when we blink than just a cleaning service.

A clue to the role of blinking is when we blink. You might think blinking is random, but it’s not. We blink at predictable times. When reading, we blink at the end of a sentence. When listening to someone talking, we blink during natural pauses in speaking. And when watching a movie, we blink during scenes when the action lags. Perhaps just after something important has happened or when the main character is briefly out of shot. And what’s more, if we’re watching with friends, our blinks tend to be synchronised with theirs. One fascinating study found skilled magicians take advantage of synchronised blinking to hide the secret of their illusions.

A moment of calm

Scientists interested in the timing of our blinks measured people’s brain activity while watching Mr. Bean. (Apparently Rowan Atkinson is very effective at synchronising blinks). The idea was to work out which parts of the brain were more or less active during blinking. They found that during blinking, there’s a spike in activity in the areas of our brain involved with the ‘default mode of brain function’. Default mode is how your brain operates when you’re in a state of calm, wakeful rest, not distracted by what’s going on in the outside world. It’s the same mode of brain function often brought on by silence. Perhaps blinking is a way to snatch a quick mental time-out every few seconds.

To test if this little mental break is simply the result of not seeing anything for a brief moment, the researchers inserted tiny blackouts in the video – a blank screen that lasted for the same amount of time as a blink. But, looking at the brain again, the default mode didn’t kick in during the blackouts. So for our brains, blinking is more than not seeing for a moment. The researchers suggest these brief moments of calm and introspection may help us to focus and to pay more attention to the world around us when we open our eyes again.

I can see the light

An odd thing about blinking is that we’re barely aware we do it. If you were to sit in a windowless room and I turned the lights off and then on again every few seconds, I reckon you’d notice. In fact I’d be willing to bet you’d get pretty annoyed. But that’s similar to what’s happening every time you blink: the world goes dark for a moment. Yet we don’t feel as though our view of the world around us has been interrupted at all.

What is going on in our brains to allow us to be oblivious to these moments of darkness? Research out last week tested two possible answers. Firstly, that after each blink, our brain backdates what we see. In this case, we assume what we see after a blink was also true during the time our eyes were closed. Our brain simply fills in the gap. A second possibility is that our brains hold onto the image of what the world looked like before the blink and assume this to have continued during the time our eyes were closed.

To test these two possibilities, scientists used some nifty experiments involving flashing a letter on a screen. Students taking part in the study had to say how long the letter appeared on the screen when they were allowed to blink, and again when they weren’t. But the results of the study suggest neither of these theories is right. The study participants simply underestimated the time the letter was visible for when they blinked. This suggests our brains just ignore blinks, momentarily shutting down our perceptions of the outside world. What we still don’t know is how our brains make the world appear continuous despite our blinks. But I know that next time someone says to me ‘Don’t blink or you’ll miss it’, I’ll remember that a blink may be just the time-out my brain needs.

Links and stuff

• Stuff to blow your mind video: why we blink
• Radio National The Science Show: The chance of taking a blink-free photo
• How to win a staring contest
• Staring contests and dominance