Why Do You Blink?

Scientists estimate we blink about 20,000 and 30,000 times a day.  If each blink is two-tenths of a second, that means we spend around 10 percent of our waking hours with our eyes closed.

But why do we blink in the first place?  A lot of people assume it’s to keep the eye moist with tears.  Yet we blink much more often than necessary to keep our eyeballs wet, so there must be another reason.

Could there be a neurological function?    A 2013 study found that during a blink, the brain undergoes a kind of mini reset, turning off some parts connected to vision and attention.  Since attention affects our perception of time, blinks may change how time is experienced.

According to Mark Wexler, a vision researcher at the Centre National de la Recherche Scientifique and Université Paris Descartes in France, eyes act somewhat like a camera by constantly moving among focal points.  Blinks interrupt the stream of light hitting the retinas, and ultra-rapid eye movements called saccades create jarring movements of the eyeballs, yet our vision appears continuous and stable.

One possible explanation is that the brain may work differently when the eyes are closed, whether it’s a blink or sleep.  “When you go into a deep sleep, it feels like there’s something that happens to your perception of time,” Wexler says.  You wake up after what feels like just a few minutes, only to find that hours have passed.  “You’re not undergoing normal mental function, and you’re so used to it that it doesn’t seem strange,” he says.

In an upcoming study, Wexler and his collaborators decided to learn more about the relationship between blinks and time perception by confusing part of the brain’s time processing.  In one experiment, researchers asked subjects to blink as they turned the lights off in the room, switching them back on a few milliseconds after they opened their eyes again.  Afterward, they asked the participants about how long they’d thought the darkness lasted.  “We learned that during a blink, time is discounted by 50–70 percent — that is, time passes two to four times as fast when the eyes are closed than during darkness while the eyes are open,” Wexler says.  A second experiment, in which participants blinked while viewing an image of a square that briefly flashed on a screen, yielded similar results.  In both cases, Wexler says, “time seems to speed up during the blink.”

Wexler and his colleagues still aren’t quite sure why this happens, but Wexler suspects it’s something like a “slowing down of the neural metabolism,” possibly like what happens during sleep. Future studies could investigate this, although the high speed of a blink (the eyelid is the body’s fastest muscle) means the equipment would need to be very high resolution.

“There are many different kinds of clocks in the brain. When you talk about time, it’s a conglomerate of many different processes,” Wexler says.  With everything going on, having an inaccurate visual sense of time can be an advantage — the speeding up of our visual clock may be what allows us to view the world as continuous, in spite of many interruptions caused by blinking eyes.

Adapted from “Your Brain Treats a Blink Like a Nap” by Alexandra Ossola ( http://nymag.com/scienceofus/2017/06/blinking-sleep-eyes-closed-time-perception.html?).


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