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

He was using fragments of the object to intellectually deduce what it was instead of recognizing it instantly as a whole like most of us do. When shown a picture of a goat, he described it as “an animal of some kind. Maybe a dog.” Often John could perceive the generic class the object belonged to—he could tells animals from plants, for example—but could not say what specific exemplar of that class it was. These symptoms were not caused by any limitation of intellect or verbal sophistication. Here is John’s description of a carrot, which I’m sure you will agree is much more detailed than what most of us could produce:

A carrot is a root vegetable cultivated and eaten as human consumption worldwide. Grown from seed as an annual crop, the carrot produces long thin leaves growing from a root head. This is deep growing and large in comparison with the leaf growth, sometimes gaining a length of twelve inches under a leaf top of similar height when grown in good soil. Carrots may be eaten raw or cooked and can be harvested during any size or state of growth. The general shape of a carrot is an elongated cone, and its color ranges between red and yellow.

John could no longer identify objects, but he could still deal with them in terms of their spatial extent, their dimensions, and their movement. He was able to walk around the hospital without bumping into obstacles. He could even drive short distances with some help—a truly amazing feat, given all the traffic he had to negotiate. He could locate and gauge the approximate speed of a moving vehicle, although he couldn’t tell if it was a Jaguar, a Volvo, or even a truck. These distinctions prove to be irrelevant to actually driving.

When he reached home, he saw an engraving of St. Paul’s Cathedral that had been hanging on the wall for decades. He said he knew someone had given it to him but had forgotten what it depicted. He could produce an astonishingly accurate drawing, copying its every detail—including printing flaws! But even after he had done so, he still couldn’t say what it was. John could see perfectly clearly; he just didn’t know what he was seeing—which is why the flaws weren’t “flaws” for him.

John had been an avid gardener prior to his stroke. He walked out of his house and much to his wife’s surprise picked up a pair of shears and proceeded to trim the hedge effortlessly. However, when he tried to tidy up the garden, he often plucked the flowers from the ground because he couldn’t tell them from the weeds. Trimming the hedge, on the other hand, required only that John see where the unevenness was. No identification of objects was required. The distinction between seeing and knowing is illustrated well by John’s predicament.

Although an inability to know what he was looking at was John’s main problem, he had other subtler difficulties as well. For instance he had tunnel vision, often losing the proverbial forest for the trees. He could reach out and grab a cup of coffee when it was on an uncluttered table by itself, but got hopelessly muddled when confronted with a buffet service. Imagine his surprise when he discovered he had poured mayonnaise rather than cream into his coffee.

Our perception of the world ordinarily seems so effortless that we tend to take it for granted. You look, you see, you understand—it seems as natural and inevitable as water flowing downhill. Its only when something goes wrong, as in patients like John, that we realize how extraordinarily sophisticated it really is. Even though our picture of the world seems coherent and unified, it actually emerges from the activity those thirty (or more) different visual areas in the cortex, each of which mediates multiple subtle functions. Many of these areas are ones we share with other mammals but some of them “split” off at some point to become newly specialized modules in higher primates. Exactly how many of our visual areas are unique to humans isn’t clear. But a great deal more is known about them than about other higher brain regions such as the frontal lobes, which are involved in such things as morality, compassion, and ambition. A thorough understanding of how the visual system really works may therefore provide insights into the more general strategies the brain uses to handle information, including the ones that are unique to us.

A FEW YEARS ago I was at an after-dinner speech given by David Attenborough at the university aquarium in La Jolla, California, near where I work. Sitting next to me was a distinguished-looking man with a walrus moustache. After his fourth glass of wine he told me that he worked for the creation science institute in San Diego. I was very tempted to tell him that creation science is an oxymoron, but before I could do so he interrupted me to ask where I worked and what I was currently interested in.

“Autism and synesthesia these days. But I also study vision.”

“Vision? What’s there to study?”