Why Don't We Notice When We Blink?

You would think we would immediately notice if the outside world suddenly went dark every few seconds. But we rarely become aware of our blinks, even though they cause a similar reduction in the amount of light entering the eye.

So why are we not aware of the frequent mini-blackouts caused by blinks? In their study, University College London scientists devised a clever way to monitor the brain's activity under conditions in which the amount of light received by the eye was constant, regardless of blinking.

How? They placed fiber-optic lights in volunteers mouths while they wore light-proof goggles. Because the light was bright enough to pass through the roof of the mouth, the fibre could be used to illuminate the retina (through the roof of the mouth).

Therefore, the amount of light falling on the retina remained constant, even when the volunteers blinked. The researchers then performed a brain scan to measure whether the act of blinking--independently of any change in light normally caused by eyelid closure--would influence the level of light-activated brain activity.

What did the scientists fiind? When volunteers were blinking, brain activity was suppressed in areas that respond to visual input, even though the light falling onto the retina remained constant throughout the blink. So why don't we notice when we blink? It seems these brain areas are purposely suppressed so that, to put it simply, the brain simply doesn't notice when we take a blink (and therefore we're saved the annoyance of having everything appear black every few seconds).

Eurek Alert July 25, 2005

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