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

And now we need to answer the “how” question, the neural mediation of the law. When you see a large lion through foliage, the different yellow lion fragments occupy separate regions of the visual field, yet your brain glues them together. How? Each fragment excites a separate cell (or small cluster of cells) in widely separated portions of the visual cortex and color areas of the brain. Each cell signals the presence of the feature by means of a volley of nerve impulses, a train of what are called spikes. The exact sequence of spikes is random; if you show the same feature to the same cell it will fire again just as vigorously, but there’s a new random sequence of impulses that isn’t identical to the first. What seems to matter for recognition is not the exact pattern of nerve impulses but which neurons fire and how much they fire—a principle known as Müller’s law of specific nerve energies. Proposed in 1826, the law states that the different perceptual qualities evoked in the brain by sound, light, and pinprick—namely, hearing, seeing, and pain—are not caused by differences in patterns of activation but by different locations of nervous structures excited by those stimuli.

That’s the standard story, but an astonishing new discovery by two neuroscientists, Wolf Singer of the Max Planck Institute for Brain Research in Frankfurt, Germany, and Charles Gray from Montana State University, adds a novel twist to it. They found that if a monkey looks at a big object of which only fragments are visible, then many cells fire in parallel to signal the different fragments. That’s what you would expect. But surprisingly, as soon as the features are grouped into a whole object (in this case, a lion), all the spike trains become perfectly synchronized. And so the exact spike trains do matter. We don’t yet know how this occurs, but Singer and Gray suggest that this synchrony tells higher brain centers that the fragments belong to a single object. I would take this argument a step further and suggest that this synchrony allows the spike trains to be encoded in such a way that a coherent output emerges which is relayed to the emotional core of the brain, creating an “Aha! Look here, it’s an object!” jolt in you. This jolt arouses you and makes you swivel your eyeballs and head toward the object, so you can pay attention to it, identify it, and take action. It’s this “Aha!” signal that the artist or designer exploits when she uses grouping. This isn’t as far-fetched as it sounds; there are known back projections from the amygdala and other limbic structures (such as the nucleus accumbens) to almost every visual area in the hierarchy of visual processing discussed in Chapter 2. Surely these projections play a role in mediating the visual “Aha!”

The remaining universal laws of aesthetics are less well understood, but that hasn’t stopped me from speculating on their evolution. (This isn’t easy; some laws may not themselves have a function but may be byproducts of other laws that do.) In fact, some of the laws actually seem to contradict each other, which may actually turn out to be a blessing. Science often progresses by resolving apparent contradictions.

The Law of Peak Shift

My second universal law, the peak-shift effect, relates to how your brain responds to exaggerated stimuli. (I should point out that the phrase “peak shift” has a purportedly precise meaning in the animal learning literature, whereas I am using it more loosely.) It explains why caricatures are so appealing. And as I mentioned earlier, ancient Sanskrit manuals on aesthetics often use the word rasa, which translates roughly to “capturing the very essence of something.” But how exactly does the artist extract the very essence of something and portray it in a painting or a sculpture? And how does your brain respond to rasa?