Media ReleaseFrom: The Royal Society
Left-right asymmetry of the Maxwell spot centroids in adults without and with dyslexia
Dyslexia is the most common form of learning difficulty concerning more than 700 million people in the world. Although over the last decades there has been much progress in genetics, neurobiology and cognitive sciences, consensus about the origin of dyslexia remains elusive. A fundamental asymmetry is found in human vision, where one has two eyes but only one view of the world. Thanks to the Maxwell spot and using a so-called foveascope, for a first cohort of 30 students without dyslexia, the topographies of the blue cones at the center of our two foveas, which are actually part of the central nervous system, are shown to be systematically asymmetric and to determine the robust afterimage dominance introduced for each observer. By contrast, a lack of asymmetry is found in a similar cohort of 30 students, with normal ocular status but with dyslexia, inducing an undetermined afterimage dominance. This anatomical and biological signature for dyslexia seems to be a basis for understanding the phonological and visual deficits, and the lack of lateralization of the different brain connections already observed. In the absence of the necessary asymmetry, the coexistence in afterimages of both a primary image and a mirror-image is found in dyslexics, explaining their reading difficulties. However, using the small delays in the brain between the arrivals of the two images, the use of pulse-width modulation light-emitting diodes suppresses the mirror-images and the reading difficulties for dyslexics. For young children with dyslexia, anatomical diagnosis and compensations can be proposed, while for adults new strategies seem to work efficiently.