DEVELOPMENT OF A MAGNOCELLULAR FUNCTION IN GOOD AND POOR PRIMARY SCHOOL-AGE READERS

Background. Abnormal functioning of the transient visual pathway (the M-pathway) has been implicated in specific reading disability (SRD). T he aim of this study is to examine the contrast thresholds for flicker -defined form discrimination in primary school children, and to compar e its development with reading and mentation development as a means of identifying children at risk of SRD. Methods. One hundred eighty-seve n children (aged 4 to 13 years) and 22 adults (aged 18 to 45 years) we re assessed for contrast sensitivity to an illusory, flicker contrast- defined form (the letter 'E')-a task which was designed to rely to a l arge extent on magnocellular pathway function. Reading age (Neale Anal ysis of Reading) and mental age (Raven's Coloured Progressive Matrices ) were assessed in the children, who had been previously screened for clinically normal binocular vision and refractive anomalies, Results. The ability of primary school-age children to discriminate the orienta tion of the low contrast flickered letters (from a choice of 4) showed a significant improvement from kindergarten (ages 4 to 6 years) to gr ade 3 (ages 8 to 10 years) and older age groups. No significant differ ence was found between good and disabled readers (at least 1-year lag in reading readiness for the kindergarten group and 2-year lag in read ing performance for 8 to 10 and 10 to 12-year-olds). Conclusions. It a ppears that there is a developmental improvement in perceptual capacit y for tasks attributed to magnocellular function, which plateaus at th e age of about 8 to 10 years. However, despite the reported reduction of magnocellular function in specific reading disabled children, no si gnificant difference in contrast threshold for flicker-defined letter discrimination was found between good and poor readers.