Saturday, December 29, 2012

Researchers bring new focus to the science of blinking.

Today you will blink somewhere around 16,500 times. Blinking is how the body lubricates your eyes - your tears are spread across your eye so it doesn't dry out. However, the science behind blinking is more complicated than simply preventing dry eyes. We blink quite a bit more than we need to - every 3-4 seconds. If you force your eyes open for a bit longer they won't dry out and they won't stop working. So why do we blink so often, and what makes us blink? A recent study suggests that blinking may "reset" our focus, allowing us to quickly change the thing we are focusing on. A blink generally lasts only 300-400 milliseconds, but it turns out that your brain is very active during that short period of time.

From a previous study,1 the group had learned that an audience will blink at the same time while watching an episode of Mr. Bean.2 In this latest study, patients in an fMRI were shown the same video and their brain activity was monitored as they watched. During a blink the brain deactivates regions responsible for focus (called the dorsal attention network) and the activates the regions responsible for daydreaming (called the default network). In other words, every time we blink our brain enters a state of wakeful rest - a momentary daydream. This means that when your eyes open your dorsal attention network will reactivate and you will refocus on the "most important" thing.

Of course, maybe the researchers were only seeing this effect because there wasn't any visual stimulus. Maybe our brains enter a state of wakeful rest simply because it got dark when we closed our eyes. To control for this possibility the researchers also replaced short segments of the video with a black screen, simulating a blink. The deactivation/activation cycle seen while blinking didn't happen during the blackouts. This important control supports the idea that we blink to reset our focus.

A moment of speculation
I wanted to make a clean break between my reporting on what the study actually said and a few thoughts of my own. The first thing I thought of when I read this study was "How did evolution select for blinking this much? Wouldn't it be dangerous to keep our eyes closed so much?"

Imagine yourself as one of the early humans. You need to seek food and shelter to stay alive, but you also need to be wary of predators. Early humans needed to be much more vigilant of predators. If a blink lasts nearly half a second, that half a second could be the difference between life and death. What, then, would be the evolutionary pressure to select for keeping our eyes closed longer than we need to? If we blink for nearly half a second every 3-4 seconds we spend over an hour and a half of our waking day with our eyes closed. Wouldn't there be a stronger pressure for keeping our eyes open?

Don't blink. Blink and you're dead.

This study provides an explanation for the evolutionary pressure behind blinking. If our focus "resets" every time we blink, then we'll be aware of the newest threat. Every time you blink you refocus to the most important thing. If you're an early human being hunted, blinking could be the thing that saves your life.

Notes
[1] I learned a few cool things while researching for this article. While reading we generally wait for a punctuation mark to blink, women blink at the same rate as men (but women on birth control blink 32% more), and while speaking to each other we wait for pauses in speech to blink (except for those diagnosed with autism, whose blinking is unaffected by speech).
[2] I suppose the program they watch is unimportant to the study, but I'm quite happy with the researcher's choice.


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