Every few seconds, our eyes automatically blink. It's so simple and natural we don't even think about it (sorry if you're now blinking manually). But blinking is strange, at least in one regard: it doesn't get dark. You'd think that blinking so often would create intermittent lights-out phases, but that doesn't happen. Now, researchers think they know why.
Blinking and focusing
Blinking is an essential eye function, helping to lubricate eyes, spread tears across, and remove irritants from the surface of the eye. But that's not all it does. Researchers from UC Berkeley, Nanyang Technological University in Singapore, Université Paris Descartes, and Dartmouth College have found that blinking helps reposition our eyes so that we can stay focus on whatever we're viewing.
When we blink, our eyeballs roll back -- but when we open our eyes, they don't always return exactly to the same place. This misalignment prompts our eye muscles to realign our vision, which helps keep our focus. Gerrit Maus, who initiated the research, explains:
"Our eye muscles are quite sluggish and imprecise, so the brain needs to constantly adapt its motor signals to make sure our eyes are pointing where they're supposed to," Maus said.
"Our findings suggest that the brain gauges the difference in what we see before and after a blink, and commands the eye muscles to make the needed corrections."
An interesting consequence of this is that our vision doesn't get dark or blurry when this happens. This mechanism keeps our day to day vision fluent but without it, everything would seem jittery and somewhat erratic, researchers say.
"We perceive coherence and not transient blindness because the brain connects the dots for us," said study co-author David Whitney, a psychology professor at UC Berkeley.
"Our brains do a lot of prediction to compensate for how we move around in the world," said co-author Patrick Cavanagh, a professor of psychological and brain sciences at Dartmouth College. "It's like a steadicam of the mind."
Brain on autopilot
In order to reach this conclusion, researchers conducted what has to be one of the most boring experiments ever. Participants were asked to sit in a dark room for long periods, staring at a dot on a screen while infrared cameras tracked their eye movements and eye blinks in real time. Every time they blinked, the dot moved 1 cm to the right. While participants didn't consciously pick up this subtle change, their brains did, learning to reposition their vision. After 30 or so movements, their brains would predict the movement of the dot, adjusting eyesight automatically to the dot's future position. This is an interesting remark in itself, even without its implications for blinking.
"Even though participants did not consciously register that the dot had moved, their brains did, and adjusted with the corrective eye movement," Maus said.
"These findings add to our understanding of how the brain constantly adapts to changes, commanding our muscles to correct for errors in our bodies' own hardware."
Journal Reference: Gerrit W. Maus, Marianne Duyck, Matteo Lisi, Thérèse Collins, David Whitney, Patrick Cavanagh. Target Displacements during Eye Blinks Trigger Automatic Recalibration of Gaze Direction. Current Biology, 2017; DOI: 10.1016/j.cub.2016.12.029