The Tell-Tale Brain: A Neuroscientist's Quest for What Makes Us Human

Consider a picture frame hanging on the wall, slightly tilted. It elicits an immediate negative reaction that is wildly out of proportion to the deviation. The same holds for a drawer that doesn’t close completely because there’s a piece of crumpled paper wedged in it and sticking out. Or an envelope with a single tiny hair accidentally caught under the sealed portion. Or a tiny piece of lint on an otherwise flawless suit. Why we react this way is far from clear. Some of it seems to be simple hygiene, which has both learned and instinctive components. Disgust with dirty feet is surely a cultural development, while picking a piece of lint out of your child’s hair might derive from the primate grooming instinct.

The other examples, such as the tilted frame or slightly disarrayed pile of books, seem to imply that our brains have a built-in need to impose regularity or predictability, although this doesn’t explain much.

It’s unlikely that all examples of regularity or predictability embody the same law. A closely related law, for example, is our love of visual repetition or rhythm, such as floral motifs used in Indian art and Persian carpets. But it’s hard to imagine that this exemplifies the same law as our fondness for a straightly hung picture frame. The only thing the two have in common, at a very abstract level, is that both involve predictability. In each case the need for regularity or order may reflect a deeper need your visual system has for economy of processing.

Sometimes deviations from predictability and order are used by designers and artists to create pleasing effects. So why should some deviations, like a tilted frame, be ugly while others—say, a beauty spot placed asymmetrically near the angle of the mouth of Cindy Crawford, rather than being in the middle of her chin or nose—be attractive? The artist seems to strike a balance between extreme regularity, which is boring, and complete chaos. For example, if she uses a motif of repeating small flowers framing a sculpture of a goddess, she may try to break the monotony of the repetition by adding some more widely spaced large flowers to create two overlapping rhythms of different periodicity. Whether there has to be a certain mathematical relationship between the two scales of repetition and what kind of phase shifts between the two are permissible are good questions—yet to be answered.

Symmetry

Any child who has played with a kaleidoscope and any lover who has seen the Taj Mahal has been under the spell of symmetry. Yet even though designers recognize its allure and poets use it to flatter, the question of why symmetrical objects should be pretty is rarely raised.

Two evolutionary forces might explain the allure of symmetry. The first explanation is based on the fact that vision evolved mainly for discovering objects, whether for grabbing, dodging, mating, eating, or catching. But your visual field is always crammed full of objects: trees, fallen logs, splotches of color on the ground, rushing brooks, clouds, outcroppings of rocks, and on and on. Given that your brain has limited attentional capacity, what rules of thumb might it employ to ensure attention gets allocated to where it’s most needed? How does your brain come up with a hierarchy of precedence rules? In nature, “important” translates into “biological objects” such as prey, predator, member of the same species, or mate, and all such objects have one thing in common: symmetry. This would explain why symmetry grabs your attention and arouses you, and by extension, why the artist or architect can exploit this trait to good use. It would explain why a newborn baby prefers looking at symmetrical inkblots over asymmetrical ones. The preference likely taps a rule of thumb in the baby’s brain that says, in effect, “Hey, something symmetrical. That feels important. I should keep looking.”

The second evolutionary force is more subtle. By presenting a random sequence of faces with varying degrees of symmetry to college undergraduates (the usual guinea pigs in such experiments), psychologists have found that the most symmetrical faces are generally judged to be the most attractive. This in itself is hardly surprising; no one expects the twisted visage of Quasimodo to be attractive. But intriguingly, even minor deviations are not tolerated. Why?