Look at the image above. Which of the central orange circles looks bigger? Most people would say the one on the right – the one surrounded by the smaller ‘petals’. In truth, the central circles are exactly the same size. This is the Ebbinghaus illusion, named after the German psychologist Hermann Ebbinghaus. It has been around for over a century, but it still continues to expand our understanding of the brain.
Samuel Schwarzkopf from University College London has just discovered that the size of one particular part of the brain, known as primary visual cortex or V1, predicts how likely we are to fall for the illusion. V1 sits at the very back of our brains and processes the visual information that we get from our eyes. It’s extremely variable; one person’s V1 might have three times the surface area of another person’s. While many scientific studies try to average out those differences, Schwarzkopf wanted to explore them.
Right from its entrance, Disneyland is designed to cast an illusion upon its visitors. The first area – Main Street – seems to stretch for miles towards the towering castle in the distance. All of this relies on visual trickery. The castle’s upper bricks and the upper levels of Main Street’s buildings are much smaller than their ground-level counterparts, making everything seem taller. The buildings are also angled towards the castle, which makes Main Street seem longer, building the anticipation of guests.
These techniques are examples of forced perspective, a trick of the eye that makes objects seem bigger or smaller, further or closer than they actually are. These illusions were used by classical architects to make their buildings seem grander, by filmmakers to make humans look like hobbits, and by photographers to create amusing shots. But humans aren’t the only animals to use forced perspective. In the forests of Australia, the male great bowerbird uses the same illusions to woo his mate.
This article is reposted from the old WordPress incarnation of Not Exactly Rocket Science.
The idea of an out-of-body experiences seems strange and hokey – certainly not one that would grace one of the world’s top scientific journals. So it may seem surprising that two years ago, Science published not one, but two papers that considered the subject through the lens of scientific scrutiny.
Out-of-body experiences are rare and can be caused by epileptic fits, neurological conditions such as strokes and heavy drug abuse. Clearly, they are triggered when something goes wrong in our brains. And as usual for the brain, something going wrong can tell us a lot about what happens the rest of the time.
Simply put, if we very rarely have an out-of-body experience, why is it that for the most part we have ‘in-body’ experiences? It’s such a fundamental part of our lives that we often take it for granted, but there must be some mental process that ensures that our perceptions of ‘self’ are confined to our own bodies. What is it?
Two groups of scientists have taken steps to answering these questions using illusion and deception. They managed to experimentally induce mild out-of-body experiences in healthy volunteers, by using virtual reality headsets to fool people into projecting themselves into a virtual body.
A ridiculous number of science-fiction TV series and films have moments where characters exchange minds, from the brilliance of Quantum Leap to the latest season of Heroes. Body-swapping is such a staple of imaginative fiction that it’s tempting to think that it has no place being scientifically investigated. But Valeria Petkova and Henrik Ehrsson beg to differ – while actually exchanging minds is clearly impossible, these two scientists have created an illusion that can make people feel that another body – be it a mannequin or an actual person – is really theirs.
The idea that our bodies are part of ourselves is so obvious and permanent that it seems ridiculous to consider any other alternative. But some people do suffer from brain damage that prevents them from accurately recognising their own limbs, or causes them to experience out-of-body experiences. The sense of bodily ownership can even be deceived in normal, healthy people, through the use of illusions.
The most famous of these involves a rubber hand – by stroking it at the same time as a person’s real hand (which is hidden from view), you can convince them that the rubber one is actually theirs. The illusion shows that timing is important. So is point-of-view – in a previous experiment, Ehrsson showed that he could induce an out-of-body experiment in the lab by combining the simultaneous stroking of the rubber-hand illusion with virtual reality headsets to show people views of their own backs.
Petkova and Ehrsson have now taken these illusions to a new extreme, tricking people into thinking that an entire body, rather than just a mere hand, is their own. The delusion is so powerful that the person can shake hands with their own real body without breaking the spell.