The human ability to write and talk are independent systems in the brain, says a new study by researchers at the Johns Hopkins University.
Although the human ability to write evolved from our ability to speak, writing and talking are now such independent systems in the brain. Some people who cannot write a grammatically correct sentence may be able say it aloud flawlessly.
Brenda 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."
Rapp noted that actually seeing people say one thing and at the same time write another is startling and surprising, adding that people don't expect that they would produce different words in speech and writing. It's as though there were two quasi-independent language systems in the brain.
The team wanted to understand how the brain organizes knowledge of written language, reading and spelling, since that there is a genetic blueprint for spoken language but not written. 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 and if it wasn't, one might see that people don't necessarily write what they say.
Rapp said that they 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. When you damage the brain, you might damage certain morphemes but not others in writing but not speaking, or vice versa.
This understanding of how the adult brain differentiates word parts could help educators as they teach children to read and write, Rapp said. It could lead to better therapies for those suffering aphasia.
The study appears in the journal Psychological Science.