The brain holds a "visual dictionary" of words we have read, allowing quick recognition without sounding out words each time we see them, a new study finds.
The research, presented today (Nov. 14) at the annual meeting of the Society for Neuroscience in Washington, D.C., could be useful for understanding the causes of reading disorders such as dyslexia, according to the researchers. The study reveals how the brain works with words, which have both a visual, written component, and a sound-based phonology component.
"One camp of neuroscientists believes that we access both the phonology and the visual perception of a word as we read it, and that the area or areas of the brain that do one, also do the other," study leader Laurie Glezer, a postdoctoral researcher at Georgetown University Medical Center, said in a statement. "But our study proves this isn't the case."
Instead, Glezer said, the brain dispenses of sound-based processing when reading and focuses on what words look like on paper.
"What we found is that once we've learned a word, it is placed in a purely visual dictionary in the brain. Having a purely visual representation allows for the fast and efficient word recognition we see in skilled readers," Glezer said. "This study is the first demonstration of that concept."
Dictionary in the brain
To unravel the brain's reading strategies, Glezer and her colleagues had 12 volunteers read words while in a functional magnetic resonance imaging (fMRI) machine. This machine measures blood flow to various brain areas, revealing which are most active at any given moment in time.
The volunteers read words that were different, but sounded the same, such as "hair" and "hare." The fMRI results showed that these two homophones activated different neurons, much as if the two words were stored on different pages of a dictionary.
"If the sounds of the word had influence in this part of the brain we would expect to see that they activate the same or similar neurons, but this was not the case, 'hair' and 'hare' looked just as different as 'hair' and 'soup,'" Glezer said. "This suggests that all we use is the visual information of a word and not the sounds."
Visual reading and dyslexia
Glezer suspects that the finding may explain why people with the reading disorder dyslexia struggle over written words. If people with dyslexia have trouble with the initial phonological sounding out of words, then they may never transfer that laborious sounding-out process into a visual "shortcut" that allows for instant word recognition without the need for sound.
"They can't take advantage of the fast processing of words using this dictionary," Glezer said.
If Glezer's hypothesis about dyslexia turns out to be true, it could open up new avenues of treatment for the disorder, she said.
"If people with dyslexia have a problem forming this visual dictionary," Glezer said, "it may be that there could be ways of helping train children with dyslexia to form a more finely tuned visual dictionary."