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Brain reads word-by-word

Research suggests words are seen as units and processed quickly

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5:59pm, April 29, 2009
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Reading may be fundamental, but how the brain gives meaning to letters on a page has been fundamentally a mystery. Two new studies fill in some details on how the brains of proficient readers handle words.

One of the studies, published in the April 30 Neuron, suggests that a visual-processing area of the brain recognizes common words as whole units. Another study, published online April 27 in PLoS ONE, reveals that the brain operates two fast parallel systems for reading, linking visual recognition of words to speech.

Maximilian Riesenhuber, a neuroscientist at Georgetown University in Washington, D.C., wanted to know whether the brain reads words letter by letter or recognizes words as whole objects. He and his colleagues showed sets of real words or nonsense words to volunteers undergoing fMRI scans. The words differed in only one letter, such as “farm” and “form” and “soat” and “poat,” or were completely different, such as “farm” and “coat” or “poat” and “hime.”
The researchers were particularly interested in what happens in the visual word form area, or VWFA, an area on the left side of the brain just behind the ear that is involved in recognizing words.

Riesenhuber and his colleagues found that neurons in the VWFA respond strongly to changes in real words. Changing “farm” to “form,” for example, produced as profound a change in activity as changing “farm” to “coat,” the team reports in Neuron. The area responded incrementally to single-letter changes in made-up words.

The data suggests that readers grasp real words as whole objects, rather than focusing on letters or letter combinations. And as a reader’s exposure to a word increases, the brain comes to recognize the shape of the word. Meaning is assigned after recognition in the brain, Riesenhuber says.

The researchers don’t yet know how longer and less familiar words are recognized, or if the brain can be trained to recognize nonsense words as a unit.

That the brain recognizes words as a whole is “a feasible interpretation of their data,” says Kalanit Grill-Spector, a neuroscientist at Stanford University, “but there should be some caution.” The team doesn’t explain how the VWFA manages the feat, she says, and other theories in which the brain recognizes smaller units of two, three or more letters might account for the findings.

Piers Cornelissen, a cognitive neuroscientist at the University of York in England, and his colleagues wanted to understand the whole sequence of events that occur in the brain during reading. Using a technique called magnetoencephalography, which measures magnetic fields created by electrical activity in neurons, the researchers pinpointed which parts of the brain are active when volunteers read words quietly to themselves. The technique allowed the researchers to time the activity down to the millisecond.

Some scientists have thought that the brain processes written words slowly, in “an increasingly complex hierarchy of processing, moving from squiggles on a page to meaning in your head,” Cornelissen says. But his study, in PLoS ONE, shows that words are processed quickly and involve direct connections between visual and speech-processing systems.

An area in the back of the brain that recognizes text was the first to respond, but then two other regions quickly activated. The VWFA and the region known as Broca’s area, involved in speech processing, became active within 15 milliseconds of the text recognition area when participants viewed words. But these areas did not activate when participants viewed pictures of faces and did not activate as quickly when they viewed strings of consonants.

Cornelissen thinks the results provide further evidence that the brain has two rapid reading pathways. The lexical route translates visual recognition of familiar words by the VWFA directly into meaning, he suggests. The sublexical route passes information through Broca’s area to the motor areas that control sound production. The second system would allow a person to work out unfamiliar or nonsense words by sounding them out in his or her head, he says.

The speed at which the VWFA becomes active supports the idea that the area recognizes whole words, Riesenhuber says. “It really argues for this being one shot to the system,” he says.

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