‘Visual Dictionary’ Supersedes Phonology for Skilled Readers
November 16, 2011 – A discovery by Georgetown University Medical Center (GUMC) neuroscientists about how the brain perceives words may one day help uncover the basis of reading disorders such as dyslexia.
Skilled readers recognize words at lightning speed without sounding them out because each word has been placed in a kind of visual dictionary, according to the study’s lead investigator, postdoctoral research fellow Laurie Glezer.
The visual dictionary concept rebuts the theory that our brain “sounds out” words each time we see them.
Phonology vs. Visual Perception
“One camp of neuroscientists believes that we access both the phonology and the visual perception of a word as we read them and that the area or areas of the brain that do one also do the other,” Glezer says. “But our study provides strong evidence this isn’t the case.”
The postdoctoral fellow works in the Laboratory for Computational Cognitive Neuroscience at GUMC led by co-author Maximilian Riesenhuber, associate professor of neuroscience. Xiong Jiang, GUMC research assistant professor, also served as an author on the study funded by the National Science Foundation.
“What we found is that once we’ve learned a word, it is placed in a purely visual dictionary in the brain,” Glezer says. “Having a purely visual representation allows for the fast and efficient word recognition we see in skilled readers.”
Glezer says the findings might help explain why people with dyslexia have slower, more labored reading.
“It could be that in dyslexia, because of phonological processing problems, these individuals are not ever able to develop a finely tuned visual representation of the words they have encountered before,” she says. “They can’t take advantage of the fast processing of words using this dictionary.”
Glezer and her research team tested word recognition in 13 volunteers using fMRI scans.
Hare and Hair
The researchers were able to see that words that are different, but sound the same, such as “hare” and “hair,” activate different neurons, a phenomenon akin to accessing different entries in a dictionary’s catalogue.
“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,’ ”she explains. “This suggests that all we use is the visual information of a word and not the sounds.”
Glezer says the brain first uses phonology to encode the word and match the sound with the written word. But after encountering the word a few more times, most people no longer need to employ the phonology.
“We hope these findings will serve as a foundation to examine reading disorders,” she says. “For example, if people with dyslexia have a problem forming this visual dictionary, it may be that there could be ways of helping train children with dyslexia to form a more finely tuned visual dictionary.”