came across this and thought i share;
The success of this illusion depends on your ability to focus and not be distracted. This illusion can be therefore used to determine severity of ADHD in an individual or conversely your ability to focus and hold your attention despite distractions.
Attention Deficit Hyperactivity Disorder - or ADHD - is thought to be caused by a chemical imbalance in the brain that affects attention, concentration and impulsivity.
In this illusion you must fixate on the flashing spot in the middle of the screen. As you stare at the spot the surrounding yellow spots will gradually vanish from your consciousness one by one. As soon as you let your eyes wander the effect is broken and the dots reappear. So you must focus and fixate on the flashing spot to make the dots vanish.
If you can only make 1 or 2 of the spots vanish you are easily distracted and find it difficult to hold your attention for long. Individuals diagnosed with ADHD are rarely capable of making all the dots vanish; in severe cases the individual does not observe the disappearance of any dots at all.
If you can make all the spots vanish you have a normal attention span.
However, if you can make all the spots vanish for more than five seconds your ability to hold your attention is truly extraordinary.
It is thought that only 1 in 100,000 people have the power of mind to make all the dots vanish for 10 seconds or more.
https://www.echalk.co.uk/amusements/OpticalIllusions/motionBlindness/motionBlindness.html
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