Clive Gifford’s book Eye Benders: The Science of Seeing and Believing has just been crowned winner of the Royal Society Young People’s book prize 2014, which is judged by young people. Here Clive shares some his favourite optical illusions from the book. via
You cannot explain how many optical illusions work without giving the reader an idea of the brain’s structure and performance. While some illusions are all about your eyes’ abilities and limitations, many of the most stunning and intriguing illusions occur due to an aspect of the brain’s processing of signals and the millions of judgment calls it makes. It’s all rather marvellous for something the size of a small cauliflower! Here, we start off by detailing some of the key parts of the brain, from the cerebellum to occipital lobes, the sorts of tasks they are involved in and how they interact
I have long been a fan of Ritsumeikan University psychology professor, Akiyoshi Kitaoka’s stunning motion illusions, so I was delighted that we were able to include several illusions inspired by his work in Eye Benders. If you stare directly at this image for a short while, you will see the individual leaves appear to flow or sway in unison as if caught in a light breeze
Another Kitaoka-inspired illusion, stare at all of these totally motionless discs for a few seconds and watch them seemingly rotate. Most people can stop the illusion simply by concentrating upon and focusing on a single wheel in the image. The difference in luminance between different parts of the wheels and how your eyes repeatedly scan an image, a little like a twitchy digital camera continually autofocusing and adjusting the eye’s lens, are believed to be responsible for creating the illusion of the wheels turning round
Human brains are often impressive at spotting patterns and filling in gaps in incomplete data they receive from the senses, but the brain gets in a muddle when presented withan impossible image – a visual stimulus that simply doesn’t add up. Famous impossible images include the Penrose staircase and this little beauty, courtesy of renowned cognitive scientist and author of Mind Sights, Roger Newland Shepard. With his usual love of a quick joke, Shepard entitled the illusion L’egs-istential Quandary. It is impossible to isolate the elephant’s legs from the background
How many different colours are used on this cube? If you count seven (white, yellow, blue, red, brown, green and orange), you’d not only be plumping for the most commonly given answer but you would also be wrong. There are just six colours used as the squares in the centre of the top and front face (one of which looks brown and the other orange) are actually the same colour. It is only when a piece of paper with two square holes cut or punched out is placed over the entire image to only display the central square that many finally accept the answer
This was the first sort of illusion I encountered, not surprising as illusions which play with perspective and your brain’s assessment of it, are amongst the oldest of all visual tricks. Which of these two tables is longer or are they both the same size? Take out a ruler to measure the long side of both tables. The answer may surprise you
See a cube? No, you don’t. It isn’t actually there. In its quest to make sense, recognise patterns and wrestle familiarity from visual data, your brain may superimpose a little certain something onto an image. It may place edges where none actually exist and where there is no change in texture, brightness or colour. Dr Anil Seth, who proved a remarkably helpful consultant on Eye Benders, turned me on to these subjective or illusory contour illusions, the most famous of which, the Kanisza Triangle, is also featured in the book
Which orange circle in these two patterns is the larger? You are most likely to answer theone on the right, but they’re actually the precise same size. How your brain measures the size of objects is a fascinating area. The brain scores high marks most of the time, being able to distinguish between the size of an object and its distance relative to your position. But your brain can be influenced or tricked by the scale and closeness of other objects to the object being assessed as occurs here
Stare at this grid from a slight angle for any length of time and you’ll start to see ghostly, grey blobs or squares appearing at the intersections of the white lines. If you focus hard at one intersection, the blob should disappear, showing how this mysterious effect works best in your peripheral vision. Lateral inhibition is the most commonly cited explanation for this phenomenon. In simple terms, this is all about how as neurons fire when stimulated by an image, they tend to suppress the firing of their neighbours
Finally, here’s another colour illusion which shows how your vision system can be influenced by other aspects of a scene. The lines of red and pink pixels that form a cross are actually the precise same shade of red. I remember seeing an image like this but uncaptioned and unexplained when I was starting out as a writer. It’s hugely exciting to be now investigating and communicating how such illusions work to others. Congratulations to Clive Gifford for winning the 2014 Royal Society Young People’s Book Award with Eye Benders: The Science of Seeing and Believing.
Book available on Amazon here.