So with the three overarching principles of internal logic, evolutionary function, and neural mechanics in mind, let’s see the role each of my individual laws plays in constructing a neurobiological view of aesthetics. Let’s begin with a concrete example: grouping.
The Law of Grouping
The law of grouping was discovered by Gestalt psychologists around the turn of the century. Take a moment to look again at Figure 2.7, the Dalmatian dog in Chapter 2. All you see at first is a set of random splotches, but after several seconds you start grouping some of the splotches together. You see a Dalmatian dog sniffing the ground. Your brain glues the “dog” splotches together to form a single object that is clearly delineated from the shadows of leaves around it. This is well known, but vision scientists frequently overlook the fact that successful grouping feels good. You get an internal “Aha!” sensation as if you have just solved a problem.
FIGURE 7.3 In this Renaissance painting, very similar colors (blues, dark brown, and beige) are scattered spatially throughout the painting. The grouping of similar colors is pleasing to the eye even if they are on different objects.
Grouping is used by both artists and fashion designers. In some well-known classic Renaissance paintings (Figure 7.3), the same azure blue color repeats all over the canvas as part of various unrelated objects. Likewise the same beige and brown are used in halos, clothes, and hair throughout the scene. The artist uses a limited set of colors rather than an enormous range of colors. Again, your brain enjoys grouping similar-colored splotches. It feels good, just as it felt good to group the “dog” splotches, and the artist exploits this. He doesn’t do this because he is stingy with paint or has only a limited palette. Think of the last time you selected a mat to frame a painting. If there are bits of blue in the painting you pick a matte that’s tinted blue. If there are mainly green earth tones in the painting, then a brown mat looks most pleasing to the eye.
The same holds for fashion. When you go to Nordstrom’s department store to buy a red skirt, the salesperson will advise you to buy a red scarf and a red belt to go with it. Or if you are a guy buying a blue suit, the salesperson may recommend a tie with some identical blue flecks to go with the suit.
But what’s all this really about? Is there a logical reason for grouping colors? Is it just marketing and hype, or is this telling you something fundamental about the brain? This is the “why” question. The answer is that grouping evolved, to a surprisingly large extent, to defeat camouflage and to detect objects in cluttered scenes. This seems counterintuitive because when you look around, objects are clearly visible—certainly not camouflaged. In a modern urban environment, objects are so commonplace that we don’t realize vision is mainly about detecting objects so that you can avoid them, dodge them, chase them, eat them, or mate with them. We take the familiar for granted, but just think of one of your arboreal ancestors trying to spot a lion hidden behind a screen of green splotches (a tree branch, say). Only visible are several yellow splotches of lion fragments (Figure 7.4). But your brain says (in effect), “What’s the likelihood that all these fragments are exactly the same color by coincidence? Zero. So they probably belong to one object. So let me glue them together to see what it is. Aha! Oops! It’s a lion—run!” This seemingly esoteric ability to group splotches may have made all the difference between life and death.
FIGURE 7.4 A lion seen through foliage. The fragments are grouped by the prey’s visual system before the overall outline of the lion becomes evident.
Little does the salesperson at Nordstrom’s realize that when she picks the matching red scarf for your red skirt, she is tapping into a deep principle underlying brain organization, and that she’s taking advantage of the fact that your brain evolved to detect predators seen behind foliage. Again, grouping feels good. Of course the red scarf and red skirt are not one object, so logically they shouldn’t be grouped, but that doesn’t stop her from exploiting the grouping law anyway, to create an attractive combination. The point is, the rule worked in the treetops in which our brains evolved. It was valid often enough that incorporating it as a law into visual brain centers helped our ancestors leave behind more babies, and that’s all that matters in evolution. The fact that an artist can misapply the rule in an individual painting, making you group splotches from different objects, is irrelevant because your brain is fooled and enjoys the grouping anyway.
Another principle of perceptual grouping, known as good continuation, states that graphic elements suggesting a continued visual contour will tend to be grouped together. I recently tried constructing a version of it that might be especially relevant to aesthetics (Figure 7.5). Figure 7.5b is unattractive, even though it is made of components whose shapes and arrangement are similar to Figure 7.5a, which is pleasing to the eye. This is because of the “Aha!” jolt you get from completion (grouping) of object boundaries behind occluders (7.5a, whereas in 7.5b there is irresolvable tension).
FIGURE 7.5 (a) Viewing the diagram on the left gives you a pleasing sensation of completion: The brain enjoys grouping.
(b) In the right-hand diagram, the smaller blobs flanking the central vertical blob are not grouped by the visual system, creating a sort of perceptual tension.
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!”