Brain separates our ability to talk and write

Writing and speaking are independent systems supported by different parts of the brain, meaning that someone who cannot write a grammatically correct sentence may be able to say it aloud flawlessly, scientists say.
Although the human ability to write evolved from our ability to speak, writing and talking are now independent systems in the brain, according to a team led by Johns Hopkins University cognitive scientist Brenda Rapp.
Rapp's team found that it's possible to damage the speaking part of the brain but leave the writing part unaffected - and vice versa - even when dealing with morphemes, the tiniest meaningful components of the language system including suffixes like "er," "ing" and "ed."

"Actually seeing people say one thing and - at the same time - write another is startling and surprising. We don't expect that we would produce different words in speech and writing," said Rapp, a professor in the Department of Cognitive Science in the university's Krieger School of Arts and Sciences.
"It's as though there were two quasi-independent language systems in the brain," Rapp said.
The team wanted to understand how the brain organises knowledge of written language - reading and spelling.

More specifically, they wanted to know if written language was dependent on spoken language in literate adults. If it was, then one would expect to see similar errors in speech and writing. If it wasn't, one might see that people don't necessarily write what they say.

The team, which included Simon Fischer-Baum of Rice University and Michele Miozzo of Columbia University, both cognitive scientists, studied five stroke victims with aphasia, or difficulty communicating.
Four of them had difficulties writing sentences with the proper suffixes, but had few problems speaking the same sentences. The last individual had the opposite problem - trouble with speaking but unaffected writing.
The researchers showed the individuals pictures and asked them to describe the action. One person would say, "The boy is walking," but write, "the boy is walked." Or another would say, "Dave is eating an apple" and then write, "Dave is eats an apple."

The findings showed that writing and speaking are supported by different parts of the brain - and not just in terms of motor control in the hand and mouth, but in the high-level aspects of word construction.
The study was published in the journal Psychological Science.