19th February 2019

There’s a famous saying that ‘seeing is believing’, as people will often not believe something until they have seen or experienced it for themselves. It’s almost like when someone says to you, ‘Don’t touch that, it’s hot!’ and you still feel compelled to touch it, just to find out for yourself. Yep- they weren’t lying. Definitely hot. This need to experience things for ourselves is part of what makes us human, but what if we told you that your senses aren’t always telling you the truth? ​ Our perception of reality is partly based on our senses and partly based on our brains understanding of the world. Our brains use a mixture of information from a sensory stimulus and experience to produce our perception, which isn’t always 100% accurate. When our brain misinterprets a stimulus, it’s called an ‘illusion’. Illusions aren’t necessarily a bad thing and are actually a sign that your brain can handle confusing situations well. ​ There are many different types of illusions, depending on which sense is being ‘fooled’. There are many that you may be familiar with, for example, an optical illusion, which is a deception in your vision. There also may be some that you are familiar with, but didn’t realise were illusions, for example, the infamous ‘Black and Blue Dress’ or the cold feeling in your mouth when you drink water after brushing your teeth. ​ Optical Illusions ​ Blue and Black Dress

Let’s start with the much debated ‘Blue and Black Dress’. If you aren’t familiar with this, number 1, where have you been (?!) and number 2, you may be wondering why we refer to it as the Blue and Black Dress and not the White and Gold Dress. In 2015, a picture of this dress was posted online and caused a huge divide in the online community, as many were certain it was blue and black, and others were convinced it was white and gold. Some even saw the dress change colour right before their eyes! Just to prove the split in opinion, we asked our Twitter followers what colour this dress was, and the result was an exact 50/50 split (this wasn’t planned, but was very convenient). We can confirm that the actual dress is blue and black, thanks to the colour picker tool (sorry to those in the white and gold corner). So, if it is blue and black, what caused so many people to see this dress so differently to others? The confusion in colour is due to a natural feature of human colour perception called colour constancy. This is the process that allows us to see colours correctly, under varying levels of light. This means our brain will put colour into context, so if you’re looking at a shadow, you will subconsciously brighten the colour up and if you’re looking in bright light, you will darken the colour. The picture of the dress is so close up that you can’t put the dress into context, leaving your brain to make assumptions to try to make sense of the situation. Those who see the dress as white and gold may think of the dress as being near a window, with natural light on it. As natural shadows tend to have a bluish tinge, our brains cancel out the blue colouring from the image, meaning the actual colours are perceived as brighter colours, i.e. white and gold. Those who see the dress as black and blue may be imagining the dress in an artificially lit room, with yellow light. The brain will then tone down the perception of any yellow tones, leaving the dress clearly blue and black. ​ Mint and Grey Shoe

Similarly to the dress, a picture of this shoe was posted on social media in 2017 and everyone freaked out, yet again. Using a colour picker tool, we’ve discovered this shoe is, in fact, mint and grey, not pink and white as many people thought. Like the dress situation, this is down to the way an individual perceives the room in the picture to be lit. Their brain then makes adjustments to the colours it perceives based on this assumption it’s had to make due to the lack of context in the photo. Thermal Illusion ​ Mint and Water ​ Have you ever had been chewing gum, or just brushed your teeth and then had a glass of water? If you have, you’ll be familiar with the freezing cold sensation that makes the water feel too cold to even carry on drinking! When this happens, the water doesn’t magically get colder when it meets the mint. It’s just another example of an illusion… this time, a thermal illusion. ​ The instigator of this illusion is a protein called the transient receptor potential cation channel subfamily M member 8 (or simply, TRPM8… much less of a mouthful), which is present in sensory neurons. TRPM8 is an ion channel that opens in cold temperatures, allowing positively charged ions into the neuron. The change in electrical charge causes a chain reaction which ends with the perception of coldness. ​ It just so happens that menthol (found in mint) is also able to open the TRPM8, leading to the same feeling of coldness, without a change in temperature! After eating mint, the menthol lingers in your mouth, so if you take a cold drink or breathe cold air it makes it feel twice as cold, as you have two stimuli. ​ Have you ever tried peppermint tea? You may find that despite the hot water, you still get a cold refreshing aftertaste… thanks science! Other Illusions ​ Here are some other illusions to try out: ​ Cross your index finger over your middle finger and rub your nose with both fingers. It will soon feel as though you have two noses! Try this one in front of the mirror too- the visual information will override your tactile information and stop the illusion from working!



Take a look at this spinning dancer- is she spinning to the left or right? Try focusing on something other than the dancer- has she switched directions? This is because the image is actually 2D but our brain is trying to interpret it as a 3D image.

Credit: Nobuyuki Kayahara, via Wikimedia Commons