Macknik Lab

Neuroscience is becoming familiar with the methods of magic by subjecting magic itself to scientific study --in some cases showing for the first time how some of its methods work in the brain. Many studies of magic conducted so far confirm what is known about cognition and attention from earlier work in experimental psychology. A cynic might dismiss such efforts: Why do yet another study that simply confirms what is already well known? But such criticism misses the importance and purpose of the studies. By investigating the techniques of magic, neuroscientists can familiarize themselves with methods that they can adapt to their own purposes. Indeed, we believe that cognitive neuroscience could have advanced faster had investigators probed magicians' intuitions earlier. Even today magicians may have a few tricks up their sleeves that neuroscientists have not yet adopted.

Just as the painter creates the illusion of depth on a flat canvas, our brain creates the illusion of depth based on information arriving from our essentially 2-D retinas. Visual illusions show us that color, brightness and shape are not absolute terms but are subjective, relative experiences actively created by complicated brain circuits. This is true not only of visual experiences but of any sensation. Whether we experience the feeling of “redness,” the appearance of squareness, or emotions such as love and hate, these are the results of the electrical activity of neurons in our brain.

The source of many of the world's woes might be tracked to a specific brain area responsible for identifying people that are not of our ilk. If so, a study on the neural bases of prejudice and its modulation (read abstract or download the pdf), by Jason Mitchell and Mahzarin R. Banaji, of Harvard University, and C Neil Macrae, at the University of Aberdeen in Scotland, published in Neuron in May 2006, could be as important to the burgeoning field of social cognitive neuroscience as Martin Luther King Jr.'s "I have a dream" speech was to the American civil rights movement.

When the eyes fix on something, they still jump imperceptibly in ways that turn out to be essential for seeing. For decades, scientists have debated the purpose, if any, of these so-called fixational eye movements, the largest of which are called microsaccades. Now the authors have demonstrated that microsaccades engender visibility when a person's gaze is fixed and that bigger and faster microsaccades work best. Microsaccades might also shed light on subliminal thoughts. Recent research suggests that the direction of microsaccades is biased toward objects to which people are unconsciously attracted, no matter where they are actually looking.

Our brains are exquisitely tuned to perceive, recognize and remember faces. We can easily find a friend’s face among dozens or hundreds of unfamiliar faces in a busy street. We look at each other’s facial expressions for signs of appreciation and disapproval, love and contempt. We carefully select the images to go with our Facebook profiles. And even after we have corresponded or spoken on the phone with somebody for a long time, we are often relieved when we meet him or her in person and are able to put “a face to the name.”

Alas! Poor Yorick. I knew him well. A fellow of infinite jest, of most excellent fancy; he hath borne me on his back a thousand times; and now, how abhorred in my afterimage he is! Well… that’s what Hamlet would have said, had he been holding the vintage Pear’s Soap advertisement bearing Yorick’s skull in the accompanying slide, rather than a dug up and rotting Danish cranium.

It’s Valentine’s season, which means that everywhere you look there are heart-shaped balloons, pink greeting cards and candy boxes filled with chocolate. But what is true love? Does it exist? Or is it simply a cognitive illusion, a trick of the mind? Let us count the ways. Contrary to the anatomy referenced in all of our favorite love songs, love (as with every other emotion we feel) is not rooted in the heart, but in the brain. (Unfortunately, Hallmark has no plans to mass-produce chocolate-covered arrow-pierced brains in the near future.) By better understanding how the brain falls in love, we can learn about why the brain can get so obsessed with this powerful emotion. In fact, some scientists even see love as a sort of addiction.

In an impossible figure, seemingly real objects—or parts of objects—form geometrical relations that physically cannot happen. The artist M.C. Escher, for instance, depicted reversible staircases and perpetually flowing streams, whereas mathematical physicist Roger Penrose drew his famously impossible triangle and visual scientist Dejan Todorović created an Elusive Arch that won him Third Prize of the 2005 Best Visual Illusion of the Year Contest. These effects challenge our hard-earned perception that the world around us follows certain, inviolable rules. They also reveal that our brains construct the feeling of a global percept, “or individual item we perceive,” by sewing together multiple local percepts. As long as the local relation between surfaces and objects follow the rules of nature, our brains don’t seem to mind that the global percept is impossible.

Scientists did not invent the vast majority of visual illusions. Rather, they are the work of visual artists, who have used their insights into the workings of the visual system to create visual illusions in their pieces of art. We have previously pointed out in our essays that, long before visual science existed as a formal discipline, artists had devised techniques to “trick” the brain into thinking that a flat canvas was three-dimensional, or that a series of brushstrokes in a still life was in fact a bowl of luscious fruit. Thus the visual arts have sometimes preceded the visual sciences in the discovery of fundamental vision principles, through the application of methodical—although perhaps more intuitive—research techniques. In this sense, art, illusions and visual science have always been implicitly linked.

The photoreceptors of your retina are like the CCD chip in your camera: just a matrix of light detectors. They individually respond to changes in light level, whether those changes are due to actual motion or to stationary changes in brightness. Then specialized motion-detection neurons of the brain analyze the responses from populations of photoreceptors to infer motion. So although Ben Franklin may have admonished that productive activity (action) is better than unproductive activity (motion), he was also correct in the neurobiological sense: the perception of motion need not arise from a veridical action in the world

The eyes are the windows to the soul. This fact is why we ask people to look us in the eye and tell us the truth. Or why we get worried when someone gives us the evil eye or has a wandering eye. Our everyday language is full of expressions that refer to where people around us are looking. Particularly if they happen to be looking in our direction.

How could we have missed it? Hundreds, perhaps thousands, of visual scientists, psychologists, neuroscientists, visual artists, architects, engineers and biologists all missed it—until now. The “it” in question is the Leaning Tower Illusion, discovered by Frederick Kingdom, Ali Yoonessi, and Elena Gheorghiu of McGill University. In this illusion, two identical side-by-side images of the same tilted and receding object appear to be leaning at two different angles. This incredible effect was first noticed just last year in images of the famed Leaning Tower of Pisa, but it also works with paired images of other tilted objects.

It’s a fact of neuroscience that everything we experience is actually a figment of our imagination. Although our sensations feel accurate and truthful, they do not necessarily reproduce the physical reality of the outside world. Of course, many experiences in daily life reflect the physical stimuli that enter the brain. But the same neural machinery that interprets actual sensory inputs is also responsible for our dreams, delusions and failings of memory. In other words, the real and the imagined share a physical source in the brain. So take a lesson from Socrates: “All I know is that I know nothing.”