|
Developmental Dyslexia: From genes to cognition through perception
Robert F. Dougherty
(abstract of a 1997 talk in the Psychology Department,
University of California, Santa Cruz)
Developmental dyslexia is a condition in which children of otherwise normal cognitive ability have difficulty learning to read. The difficulties learning to read are often associated with problems in writing and spelling. Children with this condition also have difficulty with phonemic processing- sounding out unfamiliar words, for example. The condition has long been believed to be heritable, as it tends to run in families. Recent research utilizing genetic linkage anlysis has shown that regions on human chromosomes 6 and 15 account for much of the heritability of this condition.
How can a gene, which simply codes a protein molecule, affect a cognitive function like reading? The answer to this question may lie in the subtle effects that this "dyslexia gene" has on both visual and auditory perception. Recent psychophysical and brain imaging studies have shown that many people with dyslexia see and hear the world a bit differently than those without the condition. While these perceptual differences are subtle, they may underlie the reading difficulty directly through the visual disturbances and/or indirectly through the auditory disturbances (which may disrupt phonemic processing during speech acquisition).
I will review the research which demonstrates a subtle perceptual processing deficit in people with developmental dyslexia. I will discuss how this research implicates the M-stream, which is one of several anatomically and functionally distinct concurrent processing streams in vision. I will also review the genetic research which implicates chromosome 6 (and possibly chromosome 15) in developmental dyslexia. Finally, speculation about the relation of one or several genes to the development of these visual and auditory M-streams will be discussed to connect the genetics to cognition through perception in developmental dyslexia.