July 30, 2011
Study Claims Dyslexia Can Impair Voice Recognition
Not only does dyslexia make it difficult for people to read, but a new study also suggests that the condition might also keep people from recognizing familiar voices.
In the study, researchers from the Massachusetts Institute of Technology (MIT) and the McGovern Institute for Brain Research discovered those suffering from the condition, which is a dysfunction in the brain's ability to convert viewed written images into meaningful language, also have difficulty picking up how different people can pronounce words differently.
"We tested voice-recognition abilities of dyslexic and control listeners for voices speaking listeners' native language or an unfamiliar language," authors Tyler K. Perrachione, Stephanie N. Del Tufo, and John D.E. Gabriel wrote in the journal Science on Friday.
"Individuals with dyslexia exhibited impaired voice-recognition abilities compared with controls only for voices speaking their native language. These results demonstrate the importance of linguistic representations for voice recognition," they added. "Humans appear to identify voices by making comparisons between talkers' pronunciations of words and listeners' stored abstract representations of the sounds in those words."
As part of their study, the MIT researchers trained two sets of subjects--one with dyslexia, and one without dyslexia--to recognize the voices of people speaking either their native tongue (English) or an unfamiliar foreign language (Mandarin Chinese).
For each language, they were taught to associate five speakers' voices with "unique cartoon avatars," and they were then tested on their ability to correctly match the dialect with the avatar.
"The neuroscientists found individuals with dyslexia were significantly worse at being able to consistently recognize the voices of the English speakers," the National Science Foundation (NSF) reported in a press release. "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," Perrachione said in a statement. "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."
That said, the researchers are still uncertain as to why dyslexia does not affect an individual's ability to produce speech, despite difficulties in processing the written and spoke work. Nonetheless, they believe that their research could help those with the condition by pinpointing reasons why they have difficulty understanding speech under certain conditions, and allowing educators to use that find was to better connect with those affected individuals.
The key element here, BBC News Science Reporter Jennifer Carpenter reports, are small sounds known as phonemes, which are the simple sounds that are used to teach youngsters how to speak.
"As we first try to form the word dog, for example, phonemes are the 'duh'-'og'-'guh' sounds that our parents prompt us to make," she said. "But as we master the ability to read, we become less reliant on recognizing these sounds to read, and eventually stop noticing them... Despite ignoring them, however, phonemes remain important for voice recognition"¦ The tiny inflections in the way people pronounce phonemes gives a listener cues to tell one voice from another."
"Our results are the first to explicitly link impairment in reading ability to impairment in ecologically processing spoken language," said Perrachione. "The results suggest that the source of a phonological deficit might be in dyslexic individuals' difficulties learning the consistent properties of speech sounds as spoken by an individual talker."
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