Change Blindness, Saccadic Masking: Eye Hacks – Oh My!


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In the above video, 75% of the people tested failed to notice that the person they were talking to was swapped with a different person during their conversation. In a similar experiment conducted by Derren Brown, about 50% of people failed to notice that a person asking them for directions was

swapped-out during their interaction. This phenomenon is referred to as Change Blindess or Inattentional Blindness – our inability to detect large changes in a scene.

We also experience some form of ‘blindness’ on a very small scale. Our brain performs something called Saccadic Masking during certain types of fast eye movements (saccades), where our vision is massively impaired during the movement, but our brain uses before and after snapshots to hide the fact that we were unable to clearly see during the movement – in effect, it is hiding the useless blurred image of movement from us.

You can see this in action with a simple experiment. Grab a friend and a mirror. Look into the mirror, and stare at one eye, then switch to the other, then back again. You won’t be able to see your eye movement (your brain is masking it), but your friend will.

For more information, check out Hack #17, Glimpse the Gaps in Your Vision (pdf) from O’Reilly’s excellent Mind Hacks book.

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Dan Zambonini

View posts by Dan Zambonini
Dan Zambonini is a co-founder at Eighty-Five Technologies Inc. Their most recent project is Docoh - SEC EDGAR Filings Search. He wrote A Practical Guide to Web App Success, the leading web application book. You can usually find him twittering on about something on Twitter at @zambonini.