What Mirror Images and Foreign Scripts Tell Us About the Reading Brain

Here’s a simple exercise. Count the number of times the letter ‘A’ appears in the sentences below. Easy enough, but, there's a catch. You have to do it without reading the words.

Ready?

One day, after Little Red Riding hood woke up, mother called her into the kitchen and handed her a basket of cakes and pastries. “Take these to grandmother. She's sick, and perhaps these cakes will make her feel better.”



If you have been reading for years, you probably found it difficult, if not impossible, to keep yourself from reading. You may have kept yourself from understanding the sentence, but odds are, you probably understood some of the words. When I try to do it, I have to blur my vision because if any letters come into focus, I automatically decode their meaning. For most adults in literate countries, reading is so well practiced that it’s reflexive. If the words are there, it's impossible not to read.

Now think about this for a minute. Here we have a completely artificial task. It’s not part of our biology – humans aren’t born with an innate reading reflex. If you raise a child on a desert island, he'll learn to eat, walk, and sleep, but odds are he won't spontaneously pick up a stick and start writing. For most of human history, written language didn't even exist. Reading as a cultural invention has only been around for a few thousand years, a snap of a finger in evolutionary terms. We have not, and will not within any of our lifetimes, evolve a genetic program for reading. Yet our brains are so adept at this skill that it becomes as reflexive as seeing itself.



That we are able to become so skilled at reading is a testament to the flexibility and plasticity of our brains. Of course, we don't start from scratch. We already have fine tuned machinery for similar tasks – we’re very good at seeing, and the trick is just to retune that machinery to the demands of reading. These demands are multiple. On one hand there’s the mapping from sound to symbol, and getting our visual and language systems to work together. But even on a basic visual level, we have to somewhat reprogram our visual systems.

For example, imagine a horse. Now in your head, imagine that the horse is standing in front of a mirror, and you're looking at its reflection. What does it look like now? Of course, it still looks like a horse. Mirror invariance, the idea that something flipped sideways is still the same object, is a core property of our visual systems, and for good reason. Imagine how confusing it would be if every time we saw something from the opposite direction, it became something different. But now, imagine the lowercase letter b. What's the mirror image of b? Now it's a completely different letter: d. In most writing systems, left-right orientation matters. When a character is flipped, we see it as something else.

So what happens when you take a brain used to making mirror generalizations and teach it to read? Any parents of school-age children could tell you. When you're first learning, you make lots of mistakes. Mirror reversal is overwhelmingly common in beginning writers, from the occasional flipped letter to whole words written as a mirror image. Kids do this spontaneously. They never actually see flipped letters in the world around them. It's as if their brains are too powerful for the task. They generalize letters to other orientations because that's what they've done with every single other object they've seen. You have to learn to recognize a letter only in a certain orientation .

With practice however, we do retrain our brains to read, and as you saw when we did the letter counting exercise, we become quite good at it. With such an ingrained skill, it makes you wonder if you can see its footprints in the brain. Does the brain of a reader look different from that of a nonreader?

To answer this question, we must first step back and see how our brain’s visual regions are organized. Much of the research in this area has been conducted by Nancy Kanwisher, a psychologist at the Massachusetts Institute of Technology. Her primary tool is fMRI, an imaging technology that allows neuroscientists to measure blood flow in the brain as people perform tasks. Since blood flow is tied to brain activity, fMRI allows us to see the patches of brain involved in different tasks. Kanwisher’s experiments often involve participants looking at different categories of images. By looking for areas that respond more to one category than another, she can find brain regions specialized in dealing with a certain image type. Using this technique, Kanwisher has found many specialized regions: a face area, a place area, and even an area that responds preferentially to body parts. It makes sense that these areas would exist. As a species, our survival has long depended on our ability to recognize and process faces, places, and body parts, so it's not surprising that we would have developed brain regions specialized for those things.

But what about words? Would they have their own region? A few years ago, Chris Baker, a researcher in Kanwisher’s lab, conducted the same type of experiment to look for a word region. Baker scanned native English speakers while they looked at different types of images, including words, line drawings, and Hebrew letters. They found that most participants did indeed have a brain region that responded more to words than objects.

This is rather remarkable, that the brain would develop a specialized area for an artificial category of images. But to fully interpret the results, we need more proof that this region developed as a result of learning to read. It could be that the region is there simply by coincidence, that the area is responding to some visual characteristic of print words regardless of whether a person is literate or not. To follow up, Baker tested monolingual English readers and bilingual English/Hebrew readers on the same experiment. If reading experience does alter the brain, you would expect English readers and English/Hebrew readers to have different brain responses to Hebrew. And this is indeed what Baker found. The bilingual readers had high activation for both Hebrew and English in their word region, while monolingual English readers only had high activation for English. Experience with a written language does indeed shape the brain’s response to that language.




 The above passage is an excerpt from my essay From Words to Brain, which follows the reading process from the moment a reader sees words on a page, through understanding the story and ultimately extracting meaning.  



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Baker CI, Liu J, Wald LL, Kwong KK, Benner T, & Kanwisher N (2007). Visual word processing and experiential origins of functional selectivity in human extrastriate cortex. Proceedings of the National Academy of Sciences of the United States of America, 104 (21), 9087-92 PMID: 17502592