Abstract: Attention-deficit/hyperactivity disorder (ADHD) is a cognitive–behavior developmental disorder. Inattention, hyperactivity and impulsivity are three major characters of ADHD. The main purpose of the present study was to investigate the covert orienting deficits in children with ADHD and the potential differences between predominantly inattentive subtype and combined subtype. This cognitive-behavioral study shed light on the impairment of both endogenous covert orienting and exogenous covert orienting mechanisms underlying children with two main kinds of ADHD subtypes. Specifically, we examined 1) the potential deficits of children with ADHD in tasks tapping into endogenous and exogenous orienting; 2) the potential differences between ADHD children of the predominantly inattentive subtype and children of the combined subtype. ADHD children diagnosed by clinicians using the DSM-IV criteria and matched normal children took part in two experiments. Experiment 1 involved an endogenous covert orienting task while Experiment 2 involved an exogenous covert orienting task.
The results showed that, compared with normal children, ADHD children had deficits in covert orienting. Moreover, results suggested that ADHD children had deficits in motor attention (related to covert preparation of limb movements) [6]. The data also showed that, ADHD children of the combined subtype and the predominantly inattentive subtype had different mode of deficits in the orienting network. Children of the combined subtype had shorter reaction time than children of the predominantly inattentive subtype in endogenous orienting. But the error rate was not significantly different between these two subtypes. There was no significant difference in reaction time in exogenous orienting. Children of combined subtype, however, had a higher error rate than children of predominantly inattentive subtype. This result suggested that combined subtype had more attention deficits in response preparation level

Key words: ADHD, subtypes, attention, attention networks, orienting