Have you ever wondered whether what you see as red is the same as what everyone else sees? Or why some people experience colours differently to others?
Our world is full of colour, yet we rarely realise just how much work our brains have to do to process the light coming streaming into our eyes, in order to turn it into colour vision.
Just occasionally, we realise we get a clue to what’s going on – but only when our vision goes wrong…
In the video below, you will see a black and white photo of a castle. The image then turns into a colour negative with a bright blue dot in the middle.
Keep your eyes focussed on the blue dot. Don’t look away. What happens next?
What’s going on?
“In one particular part of the image your eyes see a light of intense colour from just one place,” Helen Czerski explains. The clip above comes from her new series Colour: The Science of Spectrum, starting on BBC4 at 9pm on Wednesday.
“The second you see the new image, before your brain works out there’s been a change, it’s compensating for that intense colour from before.”
The effect is weird, but it’s no different to when you look at a bright light, then look away and see a fuzzy spot in the middle of your vision. Only this time it’s doing it with colour: what we’re seeing is an ‘afterimage’ of the colourised photo – green where there was purple, blue where there was yellow.
UCL physicist Dr Helen Czerski, presenter of BBC4’s Colour: The Science of Spectrum
“It’s like your brain has put some filters in, and as the scene changes it takes a while for the new setting to be understood,” Dr Czerski says.
We have three sensors in the back of our eyes, she explains, three different types of ‘cone’ cells that each respond to different parts of the colour spectrum, from blue through green to red. Together they allow us to see the entire rainbow of colours.
However, when you stare at a single colour, “one of the sensors basically stops sending messages to the brain,” Czerski explains. “When you change the light, you get loads of signals from the other two, and your brain ‘sees’ a colour that isn’t really there.”
What colour is The Dress?
Thanks to Czerski’s choice of outfit in the clip above, you’re probably already thinking back to earlier this year, when The Dress took social media by storm.
Quick recap: some people thought the dress above was black and blue, while others saw white and gold stripes. It caused quite the divide – and played perfectly into Helen Czerski’s hands.
“‘The Dress’ revealed this massive insecurity: if I point at a chair and say it’s red, and you were convinced it was blue, that really smashes your world view. If what I call red isn’t the same as what you think is red, how can we be sure we’re communicating anything at all?”
Dr Helen Czerski
When she was preparing for her BBC series, most of the questions she was asked revolved around this basic insecurity: how do I know that the colour I see is the same colour you see?
Research from MIT showed that 57 per cent of people believed the dress was blue and black, while 30 per cent saw white and gold stripes. 10 per cent saw blue and brown. Why?
Dr Helen Czerski testing The Dress with Anya Hurlbert, Professor of Visual Neuroscience at the University of Newcastle
“The basic game is that if your brain assumes the picture is being lit by natural light, it interprets it as one set of colours,” Czerski says. “If it assumes it’s being lit by artificial light, it sees another set of colours.”
There are various theories for why some people assume natural light and others artificial light: “There are hints that that might be connected to age. There has been a correlation observed between people of different ages, but it’s not perfect. It’s a general trend.
“The other thing that has been suggested is that if you work in an office environment. where everything is lit with a harsh fluorescent light, you’re more likely to assume that that’s what your looking at.
“It is probably something to do with everyone’s everyday existence, which means that they see one situation more commonly than another. If you’re not given enough information, you tend to default to whatever’s normal for you,” Czerski says.
Our eyes take in what they can, and our brains ‘fill in’ the rest. That’s the secret to optical illusions: finding moments that reveal what our brains are doing all the time without us realising.
“All these things are so fleeting,” Czerski says. “It’s a tiny instance that gives away what your brain is doing. The rest of the time it’s doing all this in the background. It’s fascinating when it happens, but it’s almost more fascinating that it almost never happens, that we don’t notice it more.”