A very unusual optical illusion is making internet users question their sight - after a simple animated image of a rotating grid made parts of the picture 'disappear'.
The illusion is down a phenomenon called motion-induced blindness (MIB), the causes of which remain disputed by science.
To see the effect, stare at the flashing green dot in the centre of the image below. After a few seconds of focusing on it, some or all of the yellow dots should fade and disappear, suddenly coming back into view again unexpectedly.
One of the leading theories suggests the illusion is caused by conflict between the contrasting characteristics of the two sides of the brain. The left side chooses a single aspect to focus on and denies the others, while the right takes over and assesses all secondary parts of the image, making the dots reappear.
Alternatively, the brain may incorrectly be interpreting the yellow dots as physical areas of poorer sight within the eye, and "expunging them from awareness", as a Yale University study about MIB puts it.
The optical illusion is a fun trick, but this explanation throws up an important question about consciousness by suggesting that humans use mental processes to experience reality - our eyes are not just passive cameras, but subject to the flaws and biases of our brains.
There's also questions of whether MIB occurs in the real-world - with some scientists pointing to the odd phenomenon of car tail lights in front of a driver 'disappearing' when a moving stream of cars with headlights on are driving down the other lane.
