The Brain’s Letterbox

Humans have likely been speaking since the dawn of the species a quarter million years ago. Over evolutionary time, the human brain has been molded for language, as regions such as Broca’s and Wernicke’s areas have become specialized for speech production and perception. These aren’t new brain structures or unique to humans, but their exact functions in our hominid ancestors and primate cousins are still unclear.\ Language has encroached on other functional areas of the brain as well. For example, the cerebellum, which coordinates the rhythmic movements of the limbs when walking, also guides the rhythmic production of syllables when talking. In short, natural selection has reprogrammed the human brain for speech. Reading, on the other hand, is an entirely different matter. Almost all of us learn our mother tongue effortlessly as a normal part of growing up. But learning to read is hard work, and many of us struggle with the task even in adulthood. In fact, reading is a very unnatural act for humans. Writing is a recent invention, going back only a few thousand years—a mere blink of the eye on the evolutionary time scale. Furthermore, the concept of universal literacy is an even more recent phenomenon, and it’s still more of a lofty goal than standard practice in many places around the world.

Your smart phone can read this, but your brain cannot.

Because the brain isn’t hardwired for reading, writing systems have to conform to the way the brain processes visual information. Primary visual cortex is located in the occipital lobe at the back of the head. An early process in visual perception is edge detection, and it’s one of the brain’s first steps in distinguishing the various objects in the visual array. This early process explains why objects in line drawings are often easier to identify than in photographs. Line drawings highlight the edges of objects so your brain doesn’t have to. Thus, the brain first interprets letters as visual, not linguistic, objects. The brain also needs a place to store information about the writing system it’s learned. Running along the bottom of the occipital lobe, where line detection takes place, and the temporal lobe, where object recognition occurs, is a structure known as the fusiform gyrus. This is an area that processes complex visual stimuli.  The fusiform gyrus processes complex visual stimuli, such as familiar faces and written words. One function of the fusiform gyrus is face recognition. This is where we store representations for the faces of the thousands of people we know. People with damage to this area can still recognize an object as a face, but they can’t tell whose face it is. So that man across the dinner table from you could be your husband of thirty years, or it could be Brad Pitt—you just never know. Also in the fusiform gyrus is the visual word form area. This is where the symbols of the writing system are stored, regardless of the language or the type of script. The visual word form area is informally known to language researchers as the brain’s letterbox. The brain hasn’t evolved to process written language the way that it has for spoken language. So the discovery of the visual word form area was quite a surprise. Even more surprising was the finding that all writing systems, including the complex Chinese script, are processed in this same area. It’s not quite clear what humans were doing with their visual word form area for hundreds of thousands of years before they started reading. Perhaps our hunter-gatherer ancestors used that portion of the brain for “reading” animal tracks and distinguishing edible from inedible plants. At any rate, writing systems have to use symbols that are similar to the kinds of information this area originally processed, and that’s why all writing systems are so similar. This recruitment of a specific brain region for use as the visual word form area is known as neuronal recycling. That is, brain areas originally designed for one function can be reorganized to perform another, somewhat similar function. It’s neuronal recycling that gives us the ability to learn all sorts of novel complex behaviors, such as driving a car or playing the piano, that our brains weren’t preprogrammed to perform. References Changizi, M. A., & Shimojo, S. (2005). Character complexity and redundancy in writing systems over human history. Proceedings of the Royal Society, B, 272, 267–275. Dehaene, S. (2009). Reading in the brain: The new science of how we read. New York: Hudson. Dehaene, S., & Cohen, L. (2011). The unique role of the visual word form area in reading. Trends in Cognitive Sciences, 15, 254–262. Perfetti, C. A., & Tan, L.-H. (2013). Write to read: The brain’s universal reading and writing network. Trends in Cognitive Sciences, 17, 56–57. Zhang, M., Li, J., Chen, C., Mei, L., Xue, G., Lu, Z., . . . Dong, Q. (2013). The contribution of the left mid-fusiform cortical thickness to Chinese and English reading in a large Chinese sample. NeuroImage, 65, 250–256. David Ludden is the author of The Psychology of Language: An Integrated Approach (SAGE Publications) About the Author: David Ludden, Ph.D., is a professor of psychology at Georgia Gwinnett College. https://www.psychologytoday.com/nz/blog/talking-apes/201501/the-brain-s-letter