Dyslexia: Cultural Diversity and Biological Unity

Abstract

The recognition of dyslexia as a neurodevelopmental disorder has been hampered by the belief that it is not a specific diagnostic entity because it has variable and culture-specific manifestations. In line with this belief, we found that Italian dyslexics, using a shallow orthography which facilitates reading, performed better on reading tasks than did English and French dyslexics. However, all dyslexics were equally impaired relative to their controls on reading and phonological tasks. Positron emission tomography scans during explicit and implicit reading showed the same reduced activity in a region of the left hemisphere in dyslexics from all three countries, with the maximum peak in the middle temporal gyrus and additional peaks in the inferior and superior temporal gyri and middle occipital gyrus. We conclude that there is a universal neurocognitive basis for dyslexia and that differences in reading performance among dyslexics of different countries are due to different orthographies.

Specific reading disability (dyslexia): what have we learned in the past four decades?

“…The hypothesis that the core phonological deficit in dyslexia is manifested in dysfunctional phonological processes receives support from the finding that reading difficulties and related phonological deficits persist across development, even in people with dyslexia who have compensated for their reading difficulties (Bruck, 1990(Bruck, , 1992(Bruck, , 1993Hatcher, Snowling, & Griffiths, 2002;Pennington, Orden, Smith, Green, & Haith, 1990). Such findings apply equally to adults with dyslexia who read in transparent languages (Paulesu et al, 2001).…”

“…In English, the diagnosis of dyslexia proceeds on the basis of a discrepancy between reading accuracy and age (or in some cases IQ). The same criteria cannot be used in transparent writing systems where accuracy levels are typically high (Paulesu et al, 2001). Rather, criteria tend to center on speed and fluency rather than error-rate.…”

The practical and principled problems with educational neuroscience.

“…For example, many fMRI studies have reported abnormal BOLD signals in the dyslexic brain; most often the temporoparietal cortex involved in phonological processes, and the ventral occipito-temporal cortex (often referred to as the visual word form area, or VWFA) involved in representing the visual forms of words (e.g., Brunswick, McCrory, Price, Frith, & Frith, 1999;Kronbichler et al, 2006;Paulesu et al, 2001;Rumsey, Nace, & Donohue, 1997;Shaywitz et al, 2007). Abnormal activation in either of these areas has been used to support the claim that phonological deficits are responsible for the dyslexia.…”

Balanced bilinguals favor lexical processing in their opaque language and conversion system in their shallow language

“…However, a better understanding of the impact of orthographic depth on the underlying brain networks would be of particular interest since the consistency of grapheme/phoneme correspondences has been shown to critically influence literacy acquisition (e.g. Ellis & Hooper, 2001;Goswami, 1998;Lallier, Carreiras, Tainturier, Savill, & Thierry, 2013), reading performance (Seymour, Aro, & Erskine, 2003) and the emergence of languagerelated disorders such as dyslexia (Goswami, 1998;Paulesu et al, 2001;Wheat, Cornelissen, Frost, & Hansen, 2010).…”