The latest app that's sweeping the web is the fiendishly addictive, and surprisingly difficult, Kuku Kube.
It has been designed to put your colour vision and eyesight to the test by showing boards of coloured squares.
On each board, one of the squares is a slightly different shade of the same colour and the aim is to find this odd square by tapping it with your finger or clicking it with the mouse.
Click the Start button below to play Kuku Kube
Kuku Kube (pictured) is available for free on Facebook, Android, iOS and on desktop browsers. Scores lower than 11 are poor, scores between 15 and 20 is 'lower than average', 21 to 30 is considered normal or average, and a score higher than 31 means your eyesight is considered great'
Although the game appears relatively simple, and starts with a board of just four coloured squares, it quickly grows to a board of up to 81 squares.
And the differentiation between the shades becomes more subtle over time.
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Share 592 sharesPlayers get a point for every correct square identified, but if they click or tap the wrong square they lose a point.
Plus, players get just 60 seconds to find the odd square on each board before the timer runs out and the game ends.
It was created by Canada-based Network365 and is available for free on Facebook, Android, iOS and on desktop browsers.
Although the game appears relatively simple, and starts with a board of just four coloured squares (left), it quickly grows (right). The differentiation between the shades becomes more subtle over time
There are eight levels, and as a player progresses the squares change orientation or add borders to make it harder. On the desktop version the game lets you continue until the timer runs out, but on the mobile apps (pictured) players can't progress until they have scored more than 20 on each level
There are eight levels, and as a player progresses the squares change orientation or add borders to make it harder.
On the desktop version the game lets you continue until the timer runs out, but on mobile apps players can't progress until they have scored more than 20 points on each level.
The app makers said scores lower than 11 are poor, scores between 15 and 20 is 'lower than average', 21 to 30 is considered normal or average, and a score higher than 31 means your eyesight is 'great.'
'This puzzle is designed to evaluate the quality of your colour vision,' said the developers, but isn't intended to replace a full or partial eye examination
'This puzzle is designed to evaluate the quality of your colour vision,' said the developers.
'You should identify the difference, if possible, and share your result with your friends.'
But they stressed: 'Even though this test can be very accurate, it should never be used to replace a doctor's visit.
'[It] provides basic information and guideline for your eyesight and colour test, and is not intended to replace a full or partial eye examination.'
Eyesight and colour was recently linked to how we perceive the world by Michael Abrash, chief scientist from Facebook-owned virtual reality (VR) experts Oculus.
He explained that humans only have three colour sensors, we can’t see infrared or ultraviolet and we have a blind spot in each eye.
‘Our visual data is actually astonishingly sparse and even if we were able to accurately record and process every photon that reaches our eyes, we’d still have too little data to be able to reconstruct the world accurately,' he said.
He used the recent black and blue/white and gold dress as an example.
‘Our visual system takes its best guess and sends that to the conscious mind,’ he continued.
COULD OUR ANCESTORS SEE THE COLOUR BLUE?
The blue and black (or gold and white) dress that sweeped the internet last month revealed just how differently two people can see the world.
But it's not just about lighting conditions or optical illusions - evidence is mounting that until we have a way to describe something, we may not see its there.
Ancient languages, for instance, didn't have a word for blue and scientists believe as a result our ancestors didn't notice the colour even existed.
In 1858 William Gladstone, who later became the British prime minister, counted the colour references in the Homer's Odyssey and found blue wasn't mentioned at all.
Black is mentioned nearly 200 times and white about 100. Red, meanwhile, is mentioned fewer than 15 times, and yellow and green fewer than 10.
And blue doesn't appear in Greek texts, the Koran, ancient Chinese stories, and an ancient Hebrew version of the Bible, according to a German philologist named Lazarus Geiger.
Egyptians, who were the only culture that could produce blue dyes, were the first ancient civilisation to have a word for the colour blue and there remain tribes today who don't have a word for blue, such as the Himba people in Namibia.
Several years ago, researchers showed some of the Himba tribe a circle with 11 green squares and one blue.
The study found they could not pick out which one was different from the others, or took much longer to make sense of it.
However, the same tribe has many different words for green. When they were shown squares with one green a different shade, they could pick it out immediately.
Researchers showed the Himba tribe in Namibia 11 green squares with one blue. The study found they couldn't pick out which was different from the others, but the same tribe has many words for green. When they were shown squares with one green a different shade, they picked it out immediately (second top left)
'The way that the brain compensates for the limited data it receives is by maintaining a model of the real world that it constantly updates as new data comes in.
'And it is that model, not the real world, that you experience and trust implicitly. We are inference machines, not objective observers.
He then showed a red and blue pill on hands that were shown on a yellow background to give an example of how this inference model breaks down.
Michael Abrash, chief scientist from Oculus recently used this image to show how vision is simply our perception of the world, but isn't realty. The pills are the same shade of grey, and the red and blue colours that people see are simply what their brains perceive, based on the rest of the information around them
The colours of the pills are the same shade of grey, and the red and blue colours that people see are simply what their brains perceive, based on the rest of the information around them.
And even when a person knows that the pills are grey, they still see them as red or blue.
‘Your visual system isn’t interested in whether the photons coming from a tile on a random image are red or blue or grey,' Mr Abrash continued.
'Knowing that didn’t keep anyone from being eaten by lions on the Savannah. What it is interested in is identifying potentially relevant features, in the real world, under a variety of conditions.
'Your visual system constantly corrects for the colours in the scene. It is reverse engineering reality rather than just recording it. The colours seen are your brain’s “best guess.”’
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