 We blink 10 to 15 times each minute |
25 July 2005
The team from University College London found the brain shut down parts of the visual system for each blink.
Writing in Current Biology, they said this was the case even if light was still entering the eyes.
The researchers said this could explain why people do not notice their own blinking, as it gave us an "uninterrupted view of the world".
A blink lasts for between 100 and 150 milliseconds. We automatically blink 10 to 15 times a minute to moisten and oxygenate the cornea.
During a blink, there is no visual input and no light, but we do not consciously recognise everything has momentarily gone dark.
The UCL team set out to discover why humans are not disturbed by these "mini blackouts".
The study used a specially-designed device to assess the effects of blinking on the brain.
'World goes dark'
The device, made with fibre optic cable, was placed in the mouths of volunteers who were wearing light proof goggles and lying in a functional magnetic resonance imaging (fMRI) brain scanner.
 The device used in the test lights up eyes through the mouth |
The optical fibre lit up the eyeballs through the roof of the mouth using a strong light - making the head glow red.
This meant that the light falling on the retina in the eye remained constant even when the participants blinked.
The scientists were then able to measure the effects of blinking on brain activity independently of the effect of eyelid closure on light entering the eye.
They found that blinking suppressed brain activity in the visual cortex and other areas of the brain - known as parietal and prefrontal - which are usually activated when people become conscious of visual events or objects in the outside world.
Davina Bristow, from UCL's Institute of Neurology, who led the research, said: "We would immediately notice if the outside world suddenly went dark, especially if it was happening every few seconds.
"But we are rarely aware of our blinks, even though they cause a similar reduction in the amount of light entering the eye, and this gives us an uninterrupted view of the world."
She added: "Transiently suppressing the brain areas involved in visual awareness during blinks may be a neural mechanism for preventing the brain from becoming aware of the eyelid sweeping down over the pupil during a blink and the world going dark."
The research was funded by the Wellcome Trust.
