The Dyslexic Advantage Read online

  As we become more familiar with the purposes and demands of a task, our need for big-picture processing gives way to a demand for greater accuracy, efficiency, speed, and automaticity. That’s where the left hemisphere comes in, with its greater ability to process the fine details that must be mastered to develop true expertise.

  One well-documented example of a right-to-left-hemisphere processing shift that occurs with training is the shift that takes place as we develop musical expertise. Researchers have shown that untrained music listeners process melodies primarily with their right hemispheres, so they can grasp the large-scale features (or gist) of the melody. By contrast, expert musicians process music more heavily with their left hemispheres, because they focus on the fine details and technical aspects of the performance.8

  This tendency to shift from right- to left-hemisphere processing as skill increases is intriguing because it suggests that the dyslexic failure to make such shifts might reflect a kind of general difficulty in acquiring expertise through practice. As we said in the last chapter, many individuals with dyslexia show precisely such a difficulty, especially in mastering rule-based skills like those involved in reading. Delays in mastering rule-based reading skills could clearly slow the development of “expert,” left-sided pathways and cause prolonged dependence on the “novice,” right-sided circuits. Similar difficulties in gaining expertise might also cause the greater right-hemisphere processing that individuals with dyslexia show with the other processing tasks we mentioned.

  If delays in developing automaticity and expertise at least partly explain why individuals with dyslexia use their right hemispheres more for many tasks, then what are the consequences of this more right-hemispheric processing style? We can begin to answer this question by looking at differences in how the right and left hemispheres process information, using language as an example.

  In 2005, Northwestern University psychologist Dr. Mark Beeman published a remarkable paper describing the differences in the ways that the two brain hemispheres process language. When the human brain is presented with a particular word, each hemisphere analyzes the word by activating its own “semantic field,” or collection of definitions and examples describing that word.9 Importantly, the semantic fields contained in the left and right hemispheres perform this analysis in significantly different ways.

  The left hemisphere activates a relatively narrow field of information, which focuses on the “primary” (or most common, and often the most literal) meaning of the word. This narrow field of meaning is particularly well suited for processing language that’s low in complexity or requires precise and rapid interpretation—like comprehending straightforward messages or following simple instructions. It’s also useful for quickly and efficiently producing language. Since speaking and writing require the rapid production of specific words (rather than blended or compound words), the less ambiguity or hesitation the better. The left hemisphere’s narrow semantic fields are ideal for such production.

  The right hemisphere, by contrast, activates a much broader field of potential meanings. These meanings include “secondary” (or more distant) word definitions and relationships, like synonyms and antonyms, figurative meanings, humorous connections, ironic meanings, examples or cases of how the word can be used or what it represents, and words with similar “styles” (e.g., formal/informal, modern/archaic) or “themes” (e.g., relating to the beach, to chemistry, to emotions, to economics). This broader pattern of activation is slower, but it’s also much richer. That’s why it’s particularly useful for interpreting messages that are ambiguous, complex, or figurative. Tasks for which the right hemisphere is particularly helpful include comprehending or producing metaphors, jokes, inferences, stories, social language, ambiguities, or inconsistencies.

  We asked Dr. Beeman to illustrate the kind of “distant connection” that the right hemispheric semantic processing is particularly good at detecting. He responded with the following example. “Consider this sentence: ‘Samantha was walking on the beach in bare feet, not knowing there was glass nearby. Then she felt pain and called the lifeguard for help.’ When most people hear that sentence, they infer that Samantha cut her foot. But notice that the sentence never explicitly states that she cut her foot, or even that she stepped on the glass. These facts have to be inferred, and these inferences are made by the right hemisphere. It produces these inferences by detecting the overlap in semantic fields between the terms bare feet, glass, and pain.”10

  The right hemisphere’s special skill in making such distant and inferential connections is just what individuals with dyslexia need when reading and listening. Decoding problems often make it hard for individuals with dyslexia to identify printed words, and problems distinguishing closely related words can cause similar difficulties with listening. As a result, individuals with dyslexia must often use contextual clues to fill in parts of messages they’ve missed. This is just what the right hemisphere is so good at. Rather than causing reading or listening problems, the dyslexia-associated increase in reliance on right-hemisphere processing is actually an ideal compensation for individuals who are struggling to process language at its most basic levels.

  The dyslexia-associated increase in right-hemisphere processing may help to explain many of the challenges and strengths that individuals with dyslexia commonly show. On the challenge side, the physically broader and more diffuse connections in the right hemisphere can lead to slower, less efficient, less accurate, and more effortful processing. This can place a greater burden on working memory, especially for tasks that require processing a great deal of fine detail. On the strength side, the broader network of connections provided by the right hemisphere favors new and creative connections, the recognition of more distant and unusual relationships, and skill in detecting inferences and ambiguities.

  These are all promising points, but there is also a significant drawback to this theory: If it is true that the “dyslexic difference” in cognition is due entirely to the greater tendency to use right-hemispheric circuits, then we would expect that training sufficient to produce a right-to-left processing shift would cause individuals with dyslexia to become “just like everyone else” in their cognitive style. But this is not, in fact, what we see.

  Consider, for example, the task of reading. Individuals with dyslexia who are trained sufficiently to produce the kind of right-to-left shift in their reading circuit that we described above usually don’t become indistinguishable from fully “normal” readers but instead become their own unique variety of highly skilled “dyslexic readers.” What we mean is that these dyslexic readers still generally read more slowly than comparably bright nondyslexics, and they also still display the same highly interconnected, gist- and context-dependent, imagery-based, big-picture reading comprehension style shown by most other individuals with dyslexia.

  This persistence of big-picture processing despite the shift from right to left hemisphere suggests that there must be some even more fundamental factor underlying the processing style of dyslexics. A likely candidate for this “deeper” factor has only recently come to light, but already it appears to be the most promising candidate yet for the source of the dyslexic advantage.

  Alterations in Microcircuitry: Big-Picture versus Fine-Detail Processing

  This fourth and final dyslexic brain difference was first recognized by Dr. Manuel Casanova of the University of Kentucky School of Medicine. For the last two decades Dr. Casanova has studied the cell-to-cell connections that link the neurons—which are the cells most responsible for information processing—in the human brain. Given his broad interests as a psychiatrist, neurologist, and neuropathologist, Dr. Casanova has examined an enormous range of different “types” of brains, including those of clinically “normal” subjects and subjects diagnosed with a variety of cognitive or psychiatric conditions—including dyslexia.11

  In analyzing the connections that link the neurons in the brain, Dr. Casanova identified one key feature that correlat
es both with a predisposition to dyslexia and with the kinds of “right-brain” cognitive style we’ve been discussing. This structural feature is an unusually broad spacing between the functional clusters of neurons in the brain’s cortex. To explain why this discovery is potentially so important, we must first review a few things about the structure and function of the cortex.

  The cortex is a thin sheet of cells that coats much of the brain’s surface. The neurons in the cortex communicate with each other using a combination of chemical and electrical signals. In the process, they give rise to many of our higher cognitive functions, like memory, language, sensation, attention, and conscious awareness.

  The cells in the cortex are organized into functional units called minicolumns : “columns” because they’re vertically arranged, and “mini” because they’re microscopic in size. Minicolumns were first discovered by researchers who inserted tiny electrodes into the brain’s cortex to record its electrical activity. When they pushed their electrodes straight down into the cortex, like a birthday candle into a cake, they found that the cells stacked right on top of each other responded to stimuli in unison. In contrast, when they inserted the electrode at an angle to the brain’s surface, those cells did not fire together. These results indicated that the cortical cells were grouped functionally into tiny columns that ran perpendicular to the surface of the brain: hence, minicolumns.

  To process more than just the most basic kinds of information, minicolumns must be linked to form circuits, just as the microchips in your computer must be linked to create complex processing functions. Of course, unlike computer chips your minicolumns aren’t soldered together. Instead, they’re connected by long projections—axons—that extend like cables from the neurons in one minicolumn to connect with neurons in others.

  When Dr. Casanova examined the arrangements of minicolumns and axons in many different brains, he found that each person showed a consistent pattern of spacing between his or her minicolumns. He also found that the degree of minicolumn spacing was distributed in the general population in a bell-shaped fashion, in which people on one end of the bell curve showed very closely packed minicolumns, while those on the other had very broadly spaced minicolumns.

  Casanova also noticed that each individual’s minicolumn spacing correlated closely with the size and length of the axons connecting the minicolumns in his or her brain: individuals with tightly spaced minicolumns sent out shorter axons that formed physically smaller or more local circuits, while persons with more widely spaced minicolumns sent out larger axons that formed physically longer-distance connections. In other words, individuals with tightly spaced minicolumns tended to form more connections between nearby minicolumns, while individuals with broadly spaced minicolumns tended to form more connections between minicolumns in distant parts of the brain.

  This “bias” toward either long-range or local connections turns out to be highly important because there are enormous differences in how the circuits formed by these connections function and in the tasks at which they excel. Local connections are especially good at processing fine details—that is, at carefully sorting and distinguishing closely related things, whether different sounds, sights, or concepts. Brains biased to form more of these shorter connections generally show a high level of skill in detail-oriented tasks that involve “extracting” the fine features of objects or ideas.

  In contrast, longer connections are generally weaker at fine-detail processing but excel at recognizing large features or concepts—that is, at big-picture tasks. Examples of big-picture tasks would include recognizing the overall form, context, or purpose of a thing or idea, synthesizing objects and ideas, perceiving relationships, and making unusual but insightful connections. Circuits formed from long connections are also useful for tasks that require problem solving—especially in new or changing circumstances—though they are slower, less efficient, and less reliable for familiar tasks and less skilled in discriminating fine details.

  Notice how closely the strengths associated with short (or local) connections match the “left-brain” processing skills we discussed in the previous section; and see how closely the strengths associated with long (or distant) connections match “right-brain” processing skills. Also notice how closely the processing style associated with longer connections—that is, “strong big-picture /weak fine-detail”—matches the cognitive style we’ve described as being common among individuals with dyslexia.

  Given these similarities, we might predict that “dyslexic brains” would tend to show a bias toward widely spaced minicolumns and physically longer brain circuits. And that is precisely what Dr. Casanova did find when he examined the connection patterns in the brains of dyslexic individuals.

  We asked Dr. Casanova to explain in simple terms why a bias toward longer connections might favor big-picture processing. He responded that higher cognitive skills arise when minicolumns are connected to form a modular system. He illustrated what this would mean using the example of a car, which has many separate components, or “modules,” such as the transmission, motor, and tires. When these modules are connected into a larger system, they can create new or emergent properties that aren’t present in any of the separate modules—such as the property of locomotion. This example illustrates how in modular systems the properties of the whole can greatly exceed the properties of the individual elements and can create new functions that wouldn’t exist if the parts were connected in some other way.

  Dr. Casanova then explained how the same thing happens in the brain when minicolumns are joined into circuits. “Depending on how you link minicolumns to themselves, you get the emergence of higher cognitive functions, like judgment, intellect, memory, orientation. Those functions weren’t there within the properties of the individual minicolumns. They emerged as the appropriate connections were made between cells in different parts of the brain. In other words, broader connections favor the formation of broadly integrated circuits, which in turn create high-level cognitive skills.”

  According to Dr. Casanova, the dyslexic bias toward long-distance connections leads both to the emergence of the big-picture processing skills we’ve mentioned and to weaknesses in fine-detail processing. One fine-detail task that Dr. Casanova cited as often being particularly hard for individuals with dyslexia is phonological processing, which, as we described in the last chapter, involves distinguishing highly similar sounds.

  Difficulties with fine-detail processing could also explain many of the challenges with listening, vision, motor function, and attention we described in the last chapter. To further explain the characteristic dyslexic pattern of strengths and weaknesses, Dr. Casanova contrasted dyslexia with another well-known cognitive pattern.

  “The brains of individuals with autism are biased toward short connections at the expense of long connections—just the opposite of dyslexia.” Not surprisingly, when we looked we found a high proportion of individuals with autism in the other tail of minicolumn spacing, where the minicolumns are closely packed. Cognitively, individuals with autism focus on particular details: they see the trees, but lose the forest. If you test patients with autism, their thinking tends to be rather concrete, and they struggle to see the broader meaning, form, or context.12 However, where they often excel is at tasks that can be performed using a tightly localized brain region, because they require only one specific function. An example would be finding Waldo in the Where’s Waldo books. This fine-detail processing task is performed entirely within one highly localized area of the visual cortex, where the tightly packed minicolumns are connected by many short axons into a local circuit that excels in fine-detail processing. With such tasks, individuals with autism often perform much better than other people.

  “On the other hand, where individuals with autism often struggle is with tasks like face recognition, which require that many different processing centers spread all around the brain work together.” This joining or ‘binding’ of distant processing centers is very hard for
individuals with autism, because they don’t easily form the necessary long-distance connections.

  “In contrast, joining distant areas of the brain together is just what individuals with dyslexia do best. As a result, individuals with dyslexia excel at drawing ideas from anything and anywhere, and at connecting different concepts together. Where they may miss the boat is in processing fine details.”

  The fact that this single variation in brain structure could predispose individuals to so many of the challenges and strengths that are associated with dyslexia strongly supports its potential importance.13 It also strongly supports our idea that dyslexic processing isn’t the result of a purposeless breakdown in function, but that it represents a valuable trade-off that’s been chosen for its special processing benefits. The specific nature of these benefits will be our subject throughout the next four parts, on the MIND strengths.

  Conclusion

  In chapters 3 and 4 we’ve reviewed four dyslexia-associated variations in brain structure and function that we believe underlie many common dyslexic challenges and strengths. We’ve raised several key themes that we’ll return to repeatedly as we go on to examine dyslexic strengths. The most important of these themes is that dyslexic brains are organized in very different ways from most nondyslexic brains because they’re intended to work in different ways and to excel at different tasks.