We blink an average of 15 times a minute. So why don’t we notice our world repeatedly going dark?

University College London scientists used fMRI brain imaging to find out. They placed light-blocking goggles on volunteers and put a strong fiber-optic light source against the roof of subjects’ mouths, which illuminated the eye through the skull. This combination created constant visual stimulation in the optic nerve and brain that blinking did not interrupt. Yet the fMRI scans showed that each blink temporarily shut down certain parts of the visual cortex. Activity was also decreased in parts of the parietal and prefrontal regions involved in consciousness and awareness of change. The act of blinking, it seems, makes the brain blind to the interruption.

Lead scientist Davina Bristow notes that this “transient suppression” mechanism may be at work in other sensory situations. “Basically you can’t tickle yourself for the same reason,” she says. “When you touch yourself, as opposed to someone or something else touching you, the response [in brain activation] is lowered.”