Though the words may be the same, for your brain, reading a sentence aloud is nothing like writing it down. Some people who have brain damage from strokes or injury might be able to write the words “Take the dog to the park,” but not say the sentence out loud, and vice versa.
This is because, as connected as writing and speaking seem (at least with alphabets like English, as opposed to Chinese logograms), the brain treats the two processes as fairly independent, a new study in the journal Psychological Science concludes.
Researchers in cognitive science and psychology from Johns Hopkins University, Rice University, and Columbia University studied five people with stroke-related aphasia, or difficulty communicating because of brain damage. Four exhibited difficulty writing but not speaking, and one had difficulty speaking but not writing. The participants looked at images and were asked to write and speak simple descriptions of what was happening.
The participants all exhibited issues with inflection—correctly saying, for instance, “the boy is walking,” but writing “the boy is walked” instead, or saying “two shirt” instead of “two shirts.” The study authors conclude that these errors in morphemes (the smallest grammatical unit of language, like “-ed” and “-ing”) reflect differences in the way the brain processes spoken versus written language, so that while brain damage may affect one process, it doesn’t impact the other.
"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," Brenda Rapp, one of the study’s authors and a cognitive scientist, explained in a press statement.
While five people isn’t typically enough for any kind of substantive research finding, this does bolster previous research about the different ways the brain processes speaking and writing, and how that can explain fluency in one area but not the other in aphasia patients.