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

FIGURE 7.8 The gull chick pecks at a disembodied beak or, a stick with a spot that is a reasonable approximation of the beak given the limits of sophistication of visual processing. Paradoxically, a stick with three red stripes is even more effective than a real beak; it is an ultranormal stimulus.

Why could such a thing happen? We really don’t know the “alphabet” of visual perception, whether in gulls or humans. Obviously, neurons in the visual centers of the gull’s brain (which have fancy Latin names like nucleus rotundum, hyperstriatum, and ectostriatum) are not optimally functioning machines; they are merely wired up in such a way that they can detect beaks, and therefore mothers, reliably enough. Survival is the only thing evolution cares about. The neuron may have a rule like “the more red outline the better,” so if you show it a long skinny stick with three stripes, the cell actually likes it even more! This is related to the peak-shift effect on rats mentioned earlier, except for one key difference: in the case of the rat responding to the skinnier rectangle, it’s perfectly obvious what rule the animal has learned and what you are amplifying. But in the case of the seagull, the stick with three stripes is hardly an exaggerated version of a real beak; it isn’t clear at all what rule you are tapping into or amplifying. The heightened response to the striped beak may be an inadvertent consequence of the way the cells are wired up rather than the deployment of a rule with an obvious function.

We need a new name for this type of stimulus, so I’ll call it an “ultranormal” stimulus (to distinguish it from “supernormal,” a phrase that already exists). The response to an ultranormal stimulus pattern (such as the three-striped beak) cannot be predicted from looking at the original (the single-spot beak). You could predict the response—at least in theory—if you knew in detail the functional logic of the circuitry in the chick’s brain that allows the rapid, efficient detection of beaks. You could then devise patterns that actually excite these neurons even more effectively than the original stimulus, so the chick’s brain goes “Wow! What a sexy beak!” Or you might be able to discover the ultranormal stimulus by trial and error, stumbling on it as Tinbergen did.

This brings me to my punch line about semiabstract or even abstract art for which no adequate theory has been proposed so far. Imagine that seagulls had an art gallery. They would hang this long thin stick with three stripes on the wall. They would call it a Picasso, worship it, fetishize it, and pay millions of dollars for it, while all the time wondering why they are turned on by it so much, even though (and this is the key point) it doesn’t resemble anything in their world. I suggest this is exactly what human art connoisseurs are doing when they look at or purchase abstract works of art; they are behaving exactly like the gull chicks.

By trial and error, intuition or genius, human artists like Picasso or Henry Moore have discovered the human brain’s equivalent of the seagull brain’s stick with three stripes. They are tapping into the figural primitives of our perceptual grammar and creating ultranormal stimuli that more powerfully excite certain visual neurons in our brains as opposed to realistic-looking images. This is the essence of abstract art. It may sound like a highly reductionist, oversimplified view of art, but bear in mind that I’m not saying that’s all there is to art, only that it’s an important component.

The same principle may apply to impressionist art—a Van Gogh or a Monet canvas. In Chapter 2, I noted that visual space is organized in the brain so that spatially adjacent points are mapped one-to-one onto adjacent points on the cortex. Moreover, out of the thirty or so areas in the human brain, a few—especially V4—are devoted primarily to color. But in the color area, wavelengths adjacent in an abstract “color space” are mapped onto adjacent points in the brain even when they are not near each other in external space. Perhaps Monet and Van Gogh were introducing peak shifts in abstract color space rather than “form space,” even deliberately smudging form when required. A black-and-white Monet is an oxymoron.