From the cigar nestled in the brickwork to ‘The Dress’, many optical illusions have left viewers around the world baffled over the years.
But the latest illusion is arguably one of the most bizarre yet.
Dr Dean Jackson, a biologist and BBC presenter, has shared a strange illusion on TikTok, which tricks your brain into thinking strawberries are red.
At the start of the video, Dr Jackson shows a picture of red strawberries on a white plate.
He then adds a cyan filter, before asking what colour you think the strawberries are.
While your inital reaction is likely ‘red’, Dr Jackson explains that the strawberries are actually now grey.
‘You’re still seeing the strawberries as red, right? Well, there is no red in that picture at all,’ he said.
‘There can’t be. Because red light won’t pass through a cyan filter. It’s impossible.’
Dr Dean Jackson, a biologist and BBC presenter, has shared a strange illusion on TikTok, which tricks your brain into thinking strawberries are red
The strange optical illusion occurs because our brains are confused by what our eyes see.
The back of the human eye contains two types of photoreceptor which allow us to respond to light shining in.
While ‘rods’ are sensitive to motion, ‘cones’ are sensitive to light, with each responding to a different colour.
In Dr Jackson’s video, the cyan filter only lets through cyan-coloured light, meaning anything else should appear grey.
But when our brain recognises that strawberries are usually red, it can interpret the grey light to appear this way.
‘As the only experience you have of strawberries as they are red, it fills in the detail for you, Dr Jackson explained.
‘But in fact, the strawberries are now grey in this picture.’
To prove this is the case, Dr Jackson goes on to diguise the strawberries by adding bars around them.
This makes it clear that with the cyan filter added, the strawberries are grey.
‘There you go – there is no red in the picture at all! The strawberries were grey all along,’ he added.
Dr Jackson’s video has been viewed more than 3.4 million times on TikTok, with several baffled viewers taking to the comments to discuss the illusion.
‘This illusion blew my mind a few years ago,’ one user wrote.
‘I still think it’s one of the best!’
Another added: ‘omg I watched the last strawberry change to grey in real time after the bars were added.’
And one joked: ‘I’m sick of my brain thinking about this stuff when I know it’s wrong.’
WHAT IS THE CAFÉ WALL OPTICAL ILLUSION?
The café wall optical illusion was first described by Richard Gregory, professor of neuropsychology at the University of Bristol, in 1979.
When alternating columns of dark and light tiles are placed out of line vertically, they can create the illusion that the rows of horizontal lines taper at one end.
The effect depends on the presence of a visible line of gray mortar between the tiles.
When alternating columns of dark and light tiles are placed out of line vertically, they can create the illusion that the rows of horizontal lines taper at one end. The effect depends on the presence of a visible line of gray mortar between the tiles
The illusion was first observed when a member of Professor Gregory’s lab noticed an unusual visual effect created by the tiling pattern on the wall of a café at the bottom of St Michael’s Hill in Bristol.
The café, close to the university, was tiled with alternate rows of offset black and white tiles, with visible mortar lines in between.
Diagonal lines are perceived because of the way neurons in the brain interact.
Different types of neurons react to the perception of dark and light colours, and because of the placement of the dark and light tiles, different parts of the grout lines are dimmed or brightened in the retina.
Where there is a brightness contrast across the grout line, a small scale asymmetry occurs whereby half the dark and light tiles move toward each other forming small wedges.
The café wall optical illusion was first described by Richard Gregory, professor of neuropsychology at the University of Bristol, in 1979. The unusual visual effect was noticed in the tiling pattern on the wall of a nearby café. Both are shown in this image
These little wedges are then integrated into long wedges with the brain interpreting the grout line as a sloping line.
Professor Gregory’s findings surrounding the café wall illusion were first published in a 1979 edition of the journal Perception.
The café wall illusion has helped neuropsychologists study the way in which visual information is processed by the brain.
The illusion has also been used in graphic design and art applications, as well as architectural applications.
The effect is also known as the Munsterberg illusion, as it was previously reported in 1897 by Hugo Munsterberg who referred to it as the ‘shifted chequerboard figure.’
It has also been called the ‘illusion of kindergarten patterns’, because it was often seen in the weaving of kindergarten students.
The illusion has been used in graphic design and art applications, as well as architectural applications, like the Port 1010 building in the Docklands region of Melbourne, Australia
