The nature of the visual deficits in developmental dyslexia

Facoetti, A.

1 Developmental & Cognitive Neuroscience Lab, General Psychology Department, University of Padova, Italy
2 Developmental Neuropsychology Unit, "E. Medea" Scientific Institute, Bosisio Parini, Lecco, Italy

Causal connections between multi-sensory attention and learning to read
Although impaired phonological processing is assumed to characterize dyslexic individuals, emerging evidence suggests that dyslexia could arise from a more basic cross-modal letter-to-speech sound integration deficit. Before the correct letter-to-speech sound integration is applied, letters have to be precisely selected from cluttering letters and global spoken word have to be segmented in their speech-sound units by efficient orienting of visual and auditory attention, respectively. Spatial attention deficits in children with dyslexia might impair their ability to focus on each successive letter in a visual word, and an extra-large letter spacing could help reading in dyslexic children. We showed that this simple manipulation of letter spacing substantially improved text reading efficiency on the fly (without any training) in a large, unselected sample of Italian and French dyslexic children. We demonstrated that only 12 hours of playing action video games-not involving any direct phonological or orthographic training-drastically improve the reading abilities of children with dyslexia. Action video games training could improve the efficiency of the Magnocellular-Dorsal pathway, because only action video games require an extraordinary speed in terms of transient events and moving objects, and an emphasis on peripheral processing. To test this prediction, we measured text reading and attentional skills in two matched groups of adult poor readers before and after a motion perceptual learning or an active control training. We found that only the group treaded with 20 hours motion perceptual learning improved their reading abilities. Attentional skills also improved during Magnocellular-Dorsal pathway training. These results showed that dorsal-attention pathway improvement can directly translate into better reading abilities, providing a new and fast remediation of dyslexia. Importantly, we showed that pre-reading visual and auditory attentional orienting (assessed by spatial cueing facilitation and temporal order judgment), in addition to speech-sound processing, and cross-modal mapping, captures about 60% of the future reading acquisition skills. All these results demonstrate the causal role of multi-sensory selective attention in reading acquisition, and suggest new approaches for early identification and efficient prevention of dyslexia.