Developmental dyslexia: Perceptual noise exclusion deficit or spatial attention dysfunction?

Developmental dyslexia (DD) is characterized by a multi-sensory perceptual noise exclusion deficit. Indeed, dyslexics typically show a specific deficit in the ability to detect relevant stimuli (the signal) when spatiotemporal irrelevant stimuli (the noise) are closely presented. However, spatial attention seems to be the crucial process involved in perceptual noise exclusion and it has shown consistently impaired in dyslexics. The aim of the present study was to verify whether a defective automatic shifting of visual attention could explain the perceptual noise exclusion deficit in children with DD. Accuracy in identifying a target was measured in 31 dyslexics and 23 normally reading children by an experimental paradigm including two attentional (focused vs unfocused) and two noise conditions (signal vs signal plus lateral noise). Our results confirm, in children with DD, a specific target identification deficit when stimuli were displayed with lateral noise. More importantly, dyslexics were specifically impaired in the signal plus lateral noise only in focused attention, suggesting that the attentional shifting process could affect the general perceptual noise exclusion mechanism in DD.