[♩INTRO].

Just stop for second, and pay attention to what your body is doing. Did you notice that?

You’ve probably blinked at least twice since the beginning of this video, but there’s a good chance you barely noticed. Your world doesn’t disappear in those few hundred milliseconds when your eyes are closed. And that’s all because of some clever tricks your brain plays on you.

As soon as your peepers close, your brain suppresses and sends a bunch of signals to fill in that moment of darkness. First, it suppresses visual input from the retina the part of the eye that collects light and sends a signal to the brain. And the way scientists figured this part out is pretty cool.

In a small study published in the journal Science in 1980, they had two participants wear light-blocking goggles, and then the researchers shined a light directly onto the participants’ retinas. But instead of shining it through the front of their eyes, they shined it through the roof of their mouths specifically, through the palatine bone, which was thin enough to let light reach the back of their eyes. During the experiment, the researchers momentarily switched off this light, either before, during, or after a blink.

And what they found was pretty surprising. Participants generally noticed when the light was switched off both when they had their eyes open and held them closed, since the light was directly hitting the back of their eyes either way. But they often didn’t notice the change when they blinked.

That suggested that the act of blinking causes the brain to suppress information from the retina. Then, it fills in that gap with whatever it last saw, in this case, with light. Using the same methods with eight participants, a 2005 follow-up experiment got even more specific.

With brain imaging, the experiment showed that the suppression happens in three main regions: the visual and prefrontal cortexes, and the parietal lobe. Dampening the visual cortex is what blocks that information from the retina. And because the parietal and prefrontal areas are involved in environmental awareness, the researchers think suppression there means we don’t even notice the action of blinking and moving our eyelids.

Finally, to fill in the gaps in visual information, a 2018 study suggests the brain relies on an area called the dorsomedial prefrontal cortex. It stores whatever you were looking at before the blink, and then uses that image to fill in the blip of darkness. That creates one continuous moving picture.

When you blink, your brain even recalibrates where your eyes should be focused afterwards based on how objects out there in the world are moving. That’s why you can blink while watching sports, and people won’t suddenly have teleported across the field. Scientists don’t have all the mechanisms pinned down for how that refocusing part happens.

But they are starting to piece together a pretty good picture of what happens when we shut our eyes, so we won’t be left in the dark. Thanks for watching this episode of SciShow! If you want to support the show and help us keep making episodes like this, one way you can do that is through channel memberships, which we recently enabled.

For around $5 a month, you can become a member and get access to some cool badges and emojis, and to our members-only posts in the community tab. As always, our videos will continue to be free for everyone, but if you want to support us by becoming a member, you can click on the little “join” button below this video. [♩OUTRO].