ASYMMETRICAL VISUAL-SPATIAL ATTENTIONAL PERFORMANCE IN ADHD - EVIDENCE FOR A RIGHT HEMISPHERIC DEFICIT

This study was designed to confirm the presence of a lateralizing defi cit in visual-spatial attention in children with ADHD, to further char acterize the nature of this deficit and to specify the likely hemisphe ric locus of dysfunction. Two versions of the covert orienting of atte ntion procedure which evaluated separately endogenous and exogenous cu ing effects were administered to 20 unmedicated children aged 9-12 wit h ADHD and 20 matched controls. Both groups also underwent thorough ps ychiatric assessment and testing using the TOVA and the Wisconsin Card Sorting Task (WCST). Children with ADHD showed an asymmetrical perfor mance deficit characterized by a loss of costs on controlled (endogeno us) attentional orienting to invalidly cued left visual field targets, The degree of cost asymmetry corp-elated negatively with the number o f categories sorted on the WCST. It was concluded that unmedicated chi ldren with ADHD show an asymmetrical performance deficit on the covert orienting procedure characterized by a disruption of right hemispheri c attentional mechanisms. This deficit may be related to diminished ri ght hemispheric frontal-striatal catecholamine activity.