Dissecting Dyslexia: Linking Reading to Voice Recognition

When people recognize voices, part of what helps make voice recognition accurate is noticing how people pronounce words differently. But individuals with dyslexia don't experience this familiar language advantage, say researchers.

The likely reason: "phonological impairment."

Tyler Perrachione with the Massachusetts Institute of Technology explains, "Even though all people who speak a language use the same words, they say those words just a little bit differently from one another-what is called 'phonetics' in linguistics."

Phonetics is concerned with the physical properties of speech. Listeners are sensitive to phonetic differences as part of what makes a person's voice unique. But individuals with dyslexia have trouble recognizing these phonetic differences, whether a person is speaking a familiar language or a foreign one, Perrachione says.

As a Ph.D. candidate in Neuroscience at MIT, Perrachione recently examined the impacts of phonological impairment through experiments funded by the National Science Foundation's Directorate for Education and Human Resources.

He and colleague Stephanie Del Tufo as well as Perrachione's MIT research advisor John Gabrieli hypothesized that if voice recognition by human listeners relies on phonological knowledge, then listeners with dyslexia would be impaired when identifying voices speaking their native language as compared to listeners without dyslexia.

They also theorized that listeners with dyslexia hearing a foreign language would be no more impaired in voice recognition than listeners without dyslexia, because both groups would lack specific familiarity with how the foreign language was supposed to sound.

The journal Science reports their findings online today in an article titled "Human voice recognition depends on language ability."

For their research study, the MIT scientists trained individuals with and without dyslexia to recognize the voices of people speaking either the listeners' native language of English or an unfamiliar foreign language, Mandarin Chinese. In each language, participants learned to associate five talkers' voices with unique cartoon avatars and were subsequently tested on their ability to correctly identify those voices.

The listeners were either typically-developing readers or individuals who experienced reading difficulties and dyslexia growing up.

The neuroscientists found individuals with dyslexia were significantly worse at being able to consistently recognize the voices of the English speakers. They were about the same as listeners without dyslexia at recognizing the Chinese voices; both groups were very poor at recognizing voices speaking an unfamiliar language.

"It is remarkable that individuals with dyslexia are no better able to identify voices speaking a familiar language than a foreign one," says Perrachione. "It is also very interesting that the reason for this is that they are less accurate at voice recognition than individuals who don't have dyslexia."