Dyslexia: Cause may be different than previously known

Iris Berent

New research has argued that dyslexia may result from impairment of a different linguistic system than previously thought.

Speech perception engages at least two linguistic systems: the phonetic system, which extracts discrete sound units from acoustic input, and the phonological system, which combines these units to form individual words.

Previously, researchers generally believed that dyslexia was caused by phonological impairment, but results from the current study, led by Iris Berent of Northeastern University in Boston, suggest that the phonetic system may actually be the cause.

“Our findings confirm that dyslexia indeed compromises the language system, but the locus of the deficit is in the phonetic, not the phonological system, as had been previously assumed,” says Berent.

In the study, Hebrew-speaking college students had difficulty discriminating between similar speech sounds, but had no problem tracking abstract phonological patterns, even for novel words, suggesting that the phonological system is intact but the phonetic system is compromised.

“Our research demonstrates that a closer analysis of the language system can radically alter our understanding of the disorder, and ultimately, its treatment,” concluded Berent.

Read the full article here

The study has been published in the open access journal PLOS ONE. DOI: 10.1371/journal.pone.0044875

Developmental Dyslexia - The Lancet

Dyslexia is a neuro-developmental disorder that is characterised by slow and inaccurate word recognition.

Dyslexia has been reported in every culture studied, and mounting evidence draws attention to cross-linguistic similarity in its neurobiological and neurocognitive bases.

Much progress has been made across research specialties spanning the behavioural, neuropsychological, neurobiological, and causal levels of analysis in the past 5 years.

From a neuropsychological perspective, the phonological theory remains the most compelling, although phonological problems also interact with other cognitive risk factors.

Work confirms that, neurobiologically, dyslexia is characterised by dysfunction of the normal left hemisphere language network and also implicates abnormal white matter development.

Studies accounting for reading experience demonstrate that many recorded neural differences show causes rather than effects of dyslexia. Six predisposing candidate genes have been identified, and evidence shows gene by environment interaction.