University Distinguished Professor of Psychology, Northeastern University; Research Neuroscientist, Massachusetts General Hospital; Lecturer in Psychiatry, Harvard Medical School
Conceptual Combination

Right now, as your eyes glide across this text, you are effortlessly understanding letters and words. How does your brain accomplish this remarkable feat, converting blobs of ink (or patterns of tiny pixels) into full-fledged ideas? Your brain uses concepts that you’ve accumulated throughout your lifetime. Each letter of the alphabet, each word, and each sequence of words that stands for an idea is represented in your brain by concepts. Even more remarkably, you can often comprehend things you’ve never seen before, like a brand new word in the middle of a sentence. You can see an unfamiliar breed of dog and still instantly know it’s a dog. How does your brain achieve these everyday marvels? The answer is: concepts in combination.

Most scientists will tell you that your brain contains a storehouse of concepts to categorize the objects and events around you. In this view, concepts are like dictionary definitions stored in your brain, such as “A pet is an animal companion that lives with you.” Each concept is said to have an unchanging core that’s shared by all individuals. Decades of research, however, show this is not the case. A concept is a dynamic pattern of neural activity. Your brain does not store and retrieve concepts—it makes concepts on the fly, as needed, in its network of billions of communicating neurons. Each time you construct the “same” concept, such as “Dog,” the neural pattern is different. This means a concept is a population of variable instances, not a single static instance, and your mind is a computational moment within a constantly predicting brain.

Whenever your brain encounters any sensory inputs, whether familiar or novel, it tries to produce an answer to the question, “What is this like?” In doing so, your brain constructs a concept out of bits and pieces of past experience. This process is called conceptual combination. Without it, you’d be experientially blind to anything you hadn’t encountered before.

Conceptual combination occurs every time your brain makes a concept for use, but it’s easiest to imagine when the combination is explicit, like the concept “Purple Elephant with Wings.” As another example, consider the science fiction movie The Matrix, when the shocking secret is revealed that the matrix is powered by electrical hookups to live human bodies. You need conceptual combination to construct the novel concept “Person as a Battery” in order to experience the horror.

The more familiar a concept—that is, the more frequently you’ve constructed it—the more efficiently your brain can make it by conceptual combination. Your brain requires less energy to construct the concept “Dog” than the combination, “Hairy, friendly, loyal animal with two eyes, four legs, and a slobbering tongue, who makes a barking sound, eats processed food from a bowl, and rescues children from danger in Disney movies.” That sort of combination is what your brain would have to do if it created the concept “Dog” for the first time. The word “dog” then helps your brain create the concept efficiently in the future. That’s what happened in recent years with the concept “Hangry,” which began as a combination of “Hungry” and “Angry” and “Irritable” but is now more efficiently constructed in many American brains.

You experience the effort of conceptual combination when you venture to a new culture full of unfamiliar concepts. Some concepts are universally known—a face is a face in any culture—but plenty are culture-specific, such as social concepts that serve as the glue for civilization. For example, in the United States, we have a concept, ”a thumbs-up gesture indicates that all is well.” Some other cultures, however, don’t have this concept; to them, the same hand gesture is an insult. These kinds of conceptual differences are a major reason why culture-switching is stressful and communication across cultures can be perilous.

Conceptual combination can also be fun. Anytime you’ve laughed at a stand-up comic who juxtaposed two unrelated ideas in a humorous way, you’re combining concepts. Innovation, the holy grail of business success, is effectively conceptual combination for profit.

Some brains are unable to do conceptual combination. Temple Grandin, one of the most eloquent writers with autism, describes her difficulties with conceptual combination in How Does Visual Thinking Work in the Mind of a Person with Autism: “When I was a child, I categorized dogs from cats by sorting the animals by size. All the dogs in our neighborhood were large until our neighbors got a Dachshund. I remember looking at the small dog and trying to figure out why she was not a cat.” Naoki Higashida, a teenager with autism, answers the question “What is this like?” by deliberately searching his memory, rather than automatically constructing the best fitting instance as most people’s brains do. “First, I scan my memory to find an experience closest to what’s happening now,” he writes in The Reason I Jump. “When I’ve found a good close match, my next step is to try to recall what I said the last time. If I’m lucky, I hit upon a usable experience and all is well.” If Naoki is unlucky, he becomes flustered, unable to communicate.

Scientists consider conceptual combination to be one of the most powerful abilities of the human brain. It’s not just for making novel concepts on the fly. It is the normal process by which your brain constructs concepts. Conceptual combination is the basis for most perception and action.