Hack 17. Glimpse the Gaps in Your Vision
Our eyes constantly dart around in extremely quick movements called saccades. During each movement, vision cuts out .
Despite the fact that the eye has a blind spot, an
These rapid jumps with the eyes are called
, and we make up to five every second. The problem is that while the eyes move in saccade all visual input is blurred. It's difficult enough for the brain to process stable visual images without having to deal with motion blur from the eye moving too. So, during saccades, it just doesn't bother.
2.6.1. In Action
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 movingonly 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
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.
2.6.2. How It Works
Saccadic suppression exists to stop the visual system being
One recent experiment proves that suppression definitely occurs before any visual information gets to the
Kai Thilo and a team from Oxford University 1 used TMS to give volunteers small illusionary spots, called phosphenes, in their vision.
When phosphenes were made at the retina, by applying TMS to the eye, saccadic suppression worked as normal. During a saccade, the phosphenes disappeared, as would be expected. The phosphenes were being treated like normal images on the retina. But when the spots were induced later in visual processing, at the cortex, saccades didn't affect them. They appeared regardless of eye movements.
So, suppression acts between the retina and the cortex, stopping visual information before the point where it would start entering conscious experience. Not being able to see during a saccade isn't the same kind of obstruction as when you don't see because your attention is elsewhere. That is what happens during change blindness
you don't notice changes because your attention is engaged by other things, but the changes are still
Instead, saccadic suppression is a more serious limitation. What happens during a saccade makes it nowhere near awareness. It's not just that you don't see it, it's that you can't.
2.6.3. End Note
2.6.4. See Also