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How the human brain separates the ability to talk and write

Posted May 9, 2015

While the human ability to write evolved from the ability to speak, writing and speaking are supported by entirely different parts of the brain, according to new research from Rice University, Johns Hopkins University and Columbia University.

Writing. Image credit: StartupStockPhotos via Pixabay, CC0 Public Domain

Writing. Image credit: StartupStockPhotos via Pixabay, CC0 Public Domain

The research shows that it is possible for stroke victims who cannot speak a grammatically correct sentence to write it perfectly, and vice versa.

“Modality and Morphology: What We Write May Not Be What We Say” is available online and will appear in an upcoming edition of the journal Psychological Science. The paper focuses on the relationship between written language (reading and spelling) and spoken language and whether or not written language depends on spoken language in literate adults.

“If written language does depend on spoken language, then one would expect to see similar errors in speech and writing,” said Simon Fischer-Baum, an assistant professor of psychology and cognitive scientist at Rice and the study’s co-author. “If not, one might see that people don’t necessarily write what they say.”

The researchers found that ultimately writing and speaking are supported by different parts of the brain — and not just in terms of motor control of the hands and mouth but in the high-level aspects of word construction. In addition, it is possible to injure the section of the brain responsible for speech but leave the part responsible for writing unharmed, and conversely, damage the writing part of the brain while leaving the speaking part unscathed.

“Intuitively, it seems like written language should be dependent on spoken language, since we learn to write after we learn to speak and learning to write involves sounding words out,” Fischer-Baum said. “But in fact, it appears as if, once we learn to write, our brains develop specialized mechanisms for written language, even for high levels of language processing.”

The study included five stroke victims with aphasia, a language disorder that affects a person’s ability to communicate. Fischer-Baum said the logic of the study is based on the idea of a double dissociation, being able to illustrate that two related mental processes are shown to function independently of each other.

“Imagine if you had two laptops that break; in one the screen stops working but the keyboard continues to work, while in the other the keyboard no longer works, but the screen still functions,” he said. “We could reasonably conclude from that separate processes are responsible for making the keyboard and the screen work. Similarly, if we can show that, after a stroke, some individuals lose the ability to put together word parts in writing, but not in speaking, while other individuals lose the ability in speaking but not in writing, we could reasonably conclude that there are separate neural and cognitive processes for word construction in written and spoken language.”

The study included three experiments. In the first, the researchers showed the participants between 80 and 120 pictures depicting scenarios such as a person carrying a fishing pole. The participants were asked to describe the pictures through speech and writing. In the second experiment, individuals were given a picture with one or three dogs and again were asked to describe the pictures by speaking and writing. In the third experiment, individuals were presented with a card on which the phrase “Today I walk” was printed. The participants were asked to convert this phrase to past tense by speaking and writing.

In the three exercises, four of the individuals had trouble writing grammatically correct sentences but had few problems speaking the same sentences correctly. The fourth individual had the opposite problem – difficulty speaking the sentences correctly but no problem writing them.

“We found that the brain is not just a ‘dumb’ machine that knows about letters and their order, but that it is ‘smart’ and sophisticated and knows about word parts and how they fit together,” said Brenda Rapp, a cognitive scientist from Johns Hopkins University and the study’s lead author. “When you damage the brain, you might damage certain morphemes (the smallest grammatical units of language) but not others in writing but not speaking, or vice versa.”

The researchers hope this understanding of how the adult brain differentiates word parts will help educators as they teach children how to read and write. In addition, they hope it will enhance therapy for individuals suffering from aphasia.

Source: Rice University

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