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

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.