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Put your face about 6 inches from a mirror and look from eye to eye. You’ll notice that while you’re obviously switching your gaze from eye to eye, you can’t see your own eyes actually moving—only the end result when they come to rest on the new point of focus. Now get someone else to watch you doing so in the mirror. They can clearly see your eyes shifting, while to you it’s quite invisible.

With longer saccades, you can consciously perceive the effect, but only just. Hold your arms out straight so your two index fingers are at opposite edges of your vision. Flick your eyes between them while keeping your head still. You can just about notice the momentary blackness as all visual input from the eyes is cut off. Saccades of this length take around 200 ms (a fifth of a second), which lies just on the threshold of conscious perception.

What if something happens during a saccade? Well, unless it’s really bright, you’ll simply not see it. That’s what’s so odd about saccades. We’re doing it constantly, but it doesn’t look as if the universe is being blanked out a hundred thousand times a day for around a tenth of a second every time.

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