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A set of sounds that create listening comprehension difficulty for people with dyslexia may have been pinpointed by researchers, reports Casey Johnston at arstechnica.com.
According to a recently published article in Proceedings of the National Academy of Science (PNAS), since dyslexia has been linked in the past to auditory processing deficits, scientists created rapid speech sounds that contained both natural and unnaturally high or low pitches.
Dyslexic students had the most trouble tracking rapidly changing consonant sounds, especially when pitch shifted.
Should the findings prove correct, speech pathologists may have a new avenue to help dyslexic students: they will target rapid consonant sounds of varying pitch in auditory training.
Many theories about what it is in the brain that gives rise to dyslexia abound. But some of the most promising involve the relationship between speech sounds and the phonetic alphabet.
One key point in the debate has been how deeply the problems originate in the brain’s information processing system.
According to some researchers, the issues go deeper than language comprehension. They may lie in the basic centers of auditory processing.
The nature of dyslexia’s auditory roots is widely questioned. Do dyslexics struggle with all speech sounds, or just certain kinds. Are there certain “no-speech” sounds that present problems as well?
Most studies don’t test the processing of these non-speech sounds, since they can be anything from simple tones to unusual or nonsense combinations of frequencies.
We are told that studies which have investigated such sounds usually don’t control for how complex the different kinds of sounds are. For example, “constitution” spoken in standard English might be formed of speech sounds, but non-speech sounds can be anything from simple tones to unusual pronunciations of words.
Researchers set up an experiment that played both consonant and vowel sounds to dyslexic participants in the study, in order to see how such individuals parse auditory cues. A set of non-dyslexic participants were a control group.
For consonant sounds, researchers played a track that rapidly alternated the sounds “ba” and “da.” For vowel sounds, they rapidly alternated between “u” and “y.”
Subjects were also played both speech and non-speech versions of both kinds of sounds. Speech versions were a naturally spoken “ba” or “y,” but non-speech versions mixed and matched different parts of the sound with the frequency altered.
For example, nonspeech “ba” might have a high-pitched /b/ finishing with a a low-pitch “aah.” Writes Johnston, “Imagine how the Count from Sesame Street might say “ba” and you get the idea.”
As in past research, they found that people with dyslexia do struggle when distinguishing between different speech consonants. However, they saw that these people track pretty well with normal people on vowels and can discern one vowel sound from another easily.
Surprisingly, the consonant-confusion problem was worse for the non-speech sounds. Pairing even slightly unnatural-sounding consonant tones in rapid succession was very confusing for dyslexics. Non-dyslexics hardly had any problems at all.
This study indicates the broader problem: there might be a sluggishness in auditory processing mechanisms when confronted with intonation variations, regardless of whether they arise from different people or situations.
And if variations in non-speech sounds are a problem, perhaps people with dyslexia may now be able to target their problems better in auditory training.
The authors of the study say that the auditory cortex is quite plastic, and with proper training, perhaps people with dyslexia may be able to learn to deal with difficult consonant sounds. And these improvements should result in better listening and reading skills.
Find the original article abstract at http://www.pnas.org/content/early/2010/05/17/0912858107.abstract
Visit Casey Johnston’s article at http://tinyurl.com/26dsskn
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