Here’s one to try out on your family and friends. Get hold of two cardboard boxes of different sizes and put a brick in each one. Check they weigh the same, then get somebody to lift them and tell you which is the heavier. The vast majority of people will say that the smaller box is heavier, even though it isn’t, and will continue to maintain that it is even after looking inside both boxes and lifting them several times.

This “perceptual size-weight illusion” is very robust. So much so that it works even if the smaller box is slightly lighter. Even labelling two identical boxes “heavy” and “light” can pull the same trick.
The exact reason for these illusions remains a mystery.

{ NewScientist | Continue reading }

artwork { Jean-Michel Basquiat, Brain, 1985 | acrylic, gresso, oil painstick, and paper collage on wood boxes with bootblack stand, twenty-seven boxes }

CAPTCHA’s idea is simple. It presents users with an image showing an obfuscated string of letters that they must type in to get an e-mail or social networking account, for instance, or to enter a comment on an online forum. The theory is that only humans can decipher the letters hidden in the image and type in the correct code, and for a time it was an effective tool to keep the bots out.

But while no one has yet come up with a computer that can fool people into thinking it’s another person, computers are great at fooling other computers. These days, malware makers and spammers regularly trick the CAPTCHA systems at big-name Web sites such as Yahoo Mail, Gmail and Craigslist, and use these sites to automate their attacks. (…)

Beginning in early 2008, crackers started getting the better of the CAPTCHA systems. In short order, Yahoo Mail’s, Gmail’s and Hotmail’s CAPTCHA defenses were cracked. (…) So with all that, can CAPTCHA be saved? (…)

Image-based CAPTCHAs still aren’t in widespread use. A few simple ones, such as KittenAuth, are starting to see use. With KittenAuth, users are presented with a grid of 12 pictures of animals and then asked to pick out, for example, the ones containing — you guessed it — kittens.

{ Computer World | Continue reading }

{ The two images of the Leaning Tower of Pisa are identical, yet one has the impression that the tower on the right leans more. scene. | Neural Correlate Society | Continue reading }

The term body image was coined by the great neurologist Henry Head and refers to a mental representation of one’s physical appearance. Constructed by the brain from past experience and present sensations, the body image is a fundamental aspect of both self-awareness self-identity, and can be disrupted in many conditions.

Disruption of the body image can have profound physical and psychological effects. For example, body image distortion is implicated in eating disorders such as anorexia nervosa, and also leads to phenomena such as phantom limb syndrome and body dysmorphic disorder; extreme cases of the latter can lead some people to request amputation of what they perceive to be a supernumery limb.  

A new study published in Current Biology now shows that visual distortions of the body image in patients suffering from chronic pain can signifiantly affect their perception of painful sensations.

{ Neurophilosophy/ScienceBlogs | Continue reading }

It goes without saying that we are capable of noticing changes to our bodies, but it’s perhaps less obvious that the way we perceive our bodies can affect them physically. The two-way nature of this link, between physicality and perception, has been dramatically demonstrated by a new study of people with chronic hand pain. Lorimer Moseley at the University of Oxford found that he could control the severity of pain and swelling in an aching hand by making it seem larger or smaller.

{ Not Exactly Rocket Science/ScienceBlogs | Continue reading }

screenshot { Goldfinger, 1964 }

In the 1960s, the British artist Bridget Riley began to develop a distinctive style characterised by simple and repetitive geometric patterns which create vivid illusions of movement and sometimes colour and often have a disorientating effect usually described by observers as “shimmering” or “flickering”. With her explorations of the dynamic nature of optical phenomena, Riley became one of the most prominent exponents of what came to be known as Op Art.

Many optical illusions are generated by the brain, and studying them has provided us with a better understanding of the workings of the visual system. (…)

The physiological basis of how illusions such as those seen in Riley’s paintings occur has long been the subject of debate. In the past few years, however, studies which use of a combination of experimental psychophysics and computational techniques suggest that these illusions are produced not in the brain but primarily because of miniscule and involuntary eye movements called microsaccades.

{ Neurophilosophy/ScienceBlogs | Continue reading }

related { Victor Vasarely }

At a major conference last year in Las Vegas, in a scientific paper published last week and another due out this week, psychologists have argued that magicians, in their age-old quest for better ways to fool people, have been engaging in cutting-edge, if informal, research into how we see and comprehend the world around us. Just as studying the mechanisms of disease reveals the workings of our body’s defenses, these psychologists believe that studying the ways a talented magician can short-circuit our perceptual system will allow us to better grasp how the system is put together.

“I think magicians and cognitive neuroscientists are getting at similar questions, but while neuroscientists have been looking at this for a few decades, magicians have been looking at this for centuries, millennia probably,” says Susana Martinez-Conde, a neuroscientist at the Barrow Neurological Institute and coauthor of one of the studies, published online last week in Nature Reviews Neuroscience. “What magicians do is light-years ahead in terms of sophistication and the power of these techniques.” (…)

A great deal of the success of a piece of magic is simply getting the audience’s attention and sending it to the wrong place - to a right hand flourishing a wand while the left secrets a ball away in a pocket or plucks a card from a sleeve. Magic shows are masterpieces of misdirection: they assault us with bright colors and shiny things, with puffs of smoke and with the constant obfuscatory patter that many magicians keep up as they perform.

For years, cognitive scientists thought of perception as like a movie camera, something that reproduced the world in its panoply of detail. Over the past decade, though, that model has been increasingly questioned. For one thing, people have a pronounced tendency to miss things that are happening right in front of them. Daniel Simons, a psychologist at the University of Illinois, did a series of now-famous studies in the late 1990s that showed the extent of this cognitive blindness. In one, people were approached by someone asking them for directions, only to have, in the middle of the conversation, that person replaced by another. Only half noticed the change.

In another study, people were shown a movie clip of two teams, one in black shirts and one in white, each passing a basketball around. The subjects were asked to count the number of passes one of the teams made. Half said afterward that they hadn’t noticed the woman in a gorilla suit who, midway through the clip, strolled through, paused, and beat her chest.

Because of work like this, a new model has arisen over the past decade, in which visual cognition is understood not as a camera but something more like a flashlight beam sweeping a twilit landscape. At any particular instant, we can only see detail and color in the small patch we are concentrating on. The rest we fill in through a combination of memory, prediction and a crude peripheral sight. We don’t take in our surroundings so much as actively and constantly construct them.

“Our picture of the world is kind of a virtual reality,” says Ronald A. Rensink, a professor of computer science and psychology at the University of British Columbia and coauthor of a paper on magic and psychology that will be published online this week in Trends in Cognitive Sciences. “It’s a form of intelligent hallucination.” (…)

The vanishing ball illusion is one of the most basic tricks a magician can learn: a ball is thrown repeatedly into the air and caught. Then, on the final throw, it disappears in midair. In fact, the magician has merely mimed the last throw, following the ball’s imagined upward trajectory with his eyes while keeping it hidden in his hand.

But if the technique is easily explained, the phenomenon itself is not. If done right, the trick actually makes observers see the ball rising into the air on the last toss and vanishing at its apex. As Rensink points out, this is something more powerful than merely getting someone to look in the wrong direction - it’s a demonstration of how easy it is to nudge the brain into the realm of actual hallucination. And cognitive scientists still don’t know exactly what’s causing it to happen.

{ Boston Globe | Continue reading }

photo { Bradini Magic Productions | more }

{ For our latest mission, we filled a subway car with identical twins, creating a human mirror. | story + video }

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Humans can see into the future, says a cognitive scientist. We do get a glimpse of events one-tenth of a second before they occur.

And the mechanism behind that can also explain why we are tricked by optical illusions.

Researcher Mark Changizi of Rensselaer Polytechnic Institute in New York says it starts with a neural lag that most everyone experiences while awake. When light hits your retina, about one-tenth of a second goes by before the brain translates the signal into a visual perception of the world.

Scientists already knew about the lag, yet they have debated over exactly how we compensate.

Changizi now says it’s our visual system that has evolved to compensate for neural delays, generating images of what will occur one-tenth of a second into the future. That foresight keeps our view of the world in the present. It gives you enough heads up to catch a fly ball. (…)

That same seer ability can explain a range of optical illusions, Changizi found. “Illusions occur when our brains attempt to perceive the future, and those perceptions don’t match reality,” Changizi said.

{ LiveScience | Continue reading }

illustration/unrelated illusion { MIT/Persci | more }

{ The small tilted rectangles are all the same shade of gray | MIT | continue reading }

{ Ian Saville holding his talking picture of Karl Marx | Photos: Jonathan Allen }