The incus, malleus and stapes are the three bones of the middle ear. They were formed before mammals existed, and still exist in their original setting–a reptile’s jaw. Nature is a great recycler of its own designs. The neuroscientist Stanislas Dehaene, a professor of cognitive psychology at the College de France, wagers that our brain performs a similar trick: it recycles its own neuronal pathways in response to new cultural objects. In Reading in the Brain: The Science and Evolution of a Human Invention (Viking; $27.95), Dehaene offers a theory about the evolution of reading and writing that suggests that, while humans did not evolve to read (writing is too young a technology, and took hold too swiftly, for that), we did invent a system that both conforms to pre-existing circuits and utterly revamps them. This contradiction points to the innate difficulty of reading. Learning to read laboriously reorganizes the brain. Dehaene has the neuroimaging to prove it.
What happened when your eyes lit upon the sentence "The incus, malleus and stapes are the three bones of the middle ear"? Since you take in only about seven to nine letters at a time, your eyes probably advanced in six steps called saccades. The letter strings stayed in focus as long as they were concentrated in the fifteen degrees of the visual field that utilize the fovea, the densest part of the retina. Experiments show that you register almost nothing of the text left and right of this fixation, though since you were reading from left to right, your right eye primed you for the next letter string. This orientation gave you a slight advantage in speed and accuracy: the right eye sent that information straight to its destination in the left hemisphere, instead of crossing the corpus callosum.
There, in the left hemisphere–in the left occipito-temporal area, to be exact–is the "visual word form area," discovered by Dehaene and Laurent Cohen. Nicknamed "the brain’s letterbox," it receives the visual input the fovea deconstructs and sends it on to the areas of the brain that decode its pronunciation and meaning. Because the sentence "The incus, malleus and stapes are the three bones of the middle ear" started off with three nouns you almost never encounter, you were slowed down a bit. Instead of directly retrieving their meaning from a lexical dictionary of fifty- to a hundred-thousand words you unconsciously maintain in your middle temporal and frontal regions, your brain processed those words through a phonological network, which converted the letter strings to sounds, employing the inferior parietal and the opercular regions. That required an additional forty milliseconds. Dehaene compares the process to a tidal bore invading a riverbed: "A known word resonates in the temporal lobe networks and produces a massive wave of synchronized oscillations that rolls through millions of neurons. This tidal bore goes even as far as the more distant regions of the cortex as it successively contacts the many assemblies of neurons that each encode a fragment of the word’s meaning."
How those fragments snapped together, and how you processed away any ambiguity in the words to arrive at the correct interpretation of a sentence, is still a mystery. But it is no mystery that it took the brain years to learn the process. You probably remember your early schooling in the alphabet song, letters and numbers, and handwriting practice. The process went on much longer than that: your neurons went on building a mental lexicon, compiling statistics about the prosodic and spelling patterns in your language, and coordinating the different networks that recognize meaning and sound so that they could work in close association. The granularity of this knowledge can’t be summed up easily: any language consists of untold numbers of arbitrary, infinitesimal differences. It calls on one part of the brain to, say, distinguish pair and pear, another to pair pair and couple, and another to suppress the arbitrary difference between pear and PEAR, or "pear" as it is printed here and its cursive version. And that’s just ambiguity at the level of the word. Yet the process is virtually instantaneous: reading, "from retinal processing to the highest level of abstraction and invariance, thus unfolds automatically, in less than one-fifth of a second, without any conscious examination." Given this daunting labor, the person who assays Reading in the Brain might be likely to pat herself on the back, while someone else might feel justified in throwing up her hands and clicking on a podcast. Reading and writing sounds more rewarding to us as a species than as individuals.