In the Middle Ages, people invoked excitement, they called it forward, controlled it, by singing the psalms. Nowadays, we push a button, flip a switch, swallow a pill, inject with a needle, to have it pay a visit – and the age of the agent does not seem to matter. The images come flying – hundreds, thousands of images, relentlessly come flying at us. The imagination becomes a warehouse for storing, rather than an instrument for conjuring. One has to shake off the rush of simulated reality. But it’s hard to return to a world washed clean of special effects. The images linger from the electronic realm, the emotions still stirred, demanding some discharge.

I have also argued that the best, most strenuous exercise of the imagination comes through reading. But reading is slow and cumbersome; it lacks the pizzazz of thrill rides, extreme sports, and video games. Open a page: everything’s flat and utterly still. The words do not move. If anything moves, it’s the reader. Just watch kids fidget when they read; they follow the words and rock, like Hassidic Jews praying in shul. Kids love to move; they need to. It’s in their bodies that they find the rhythm of prose. After all, the music’s called rock and roll. Hip hop. (The metre of poetry is divided into feet, and those feet derive their names from dance steps.)

But the great, important movement remains out of view, invisible, acted out in the mind’s eye, or played out in the mind’s living room or rumpus room, or even gymnasium. The reason so many novels and poems and fairy tales involve pilgrimages, voyages, and road trips – from Chaucer to Kerouac – is that movement means that time has passed, and elapsed time implies change – emotional change, one of the hardest things to dramatize. We see Huck as a different boy at the end of his drift down the Mississippi – he thinks differently, he feels different. He knows it. He wants more. He cannot get any bigger without lighting out for the territory. Immensity is all. America’s the place to expand. It always has been.

The metaphors we use to capture the nature of thought: I came to this decision, I arrived at this conclusion, let me walk you through this argument. In the Renaissance, people devised mnemonic tricks as memory aides. The favourite one turned the inside of one’s head into a house, divided it into rooms, and placed objects from a list that one wished to memorize in those rooms. To recall the list, one merely walked through each room and re-collected the objects. Three hundred years ago, people played with interior space; it became a form of entertainment.