Severity of AD/HD symptoms and efficiency of attentional resource allocation.

This study investigated the mechanism that underlies the inefficient allocation of attentional resources in Attention-Deficit/Hyperactivity Disorder (AD/HD). The P300 event-related brain potential (ERP) was elicited from 24 healthy adults using a visual three-stimulus oddball paradigm (standard, 70%; target, 15%; non-target, 15%) and the degree of their AD/HD symptoms was assessed by using AD/HD symptom scales. Target stimulus was a circle and standard stimulus was an "X". Two task conditions were defined according to the non-target stimulus type (typical or novel): a triangle for the typical condition and colored non-repetitive novel stimuli for the novel condition. In both conditions, target and non-target elicited P300s. A ratio of non-target P300 to target P300 amplitude was used to assess the efficiency of attentional resource allocation; low ratio indicates the efficient allocation of attentional resource. The correlation analysis revealed a strong positive correlation between the AD/HD symptom score and the P300 amplitude ratio in the typical condition (r=.80), while only a weak positive correlation was observed in the novel condition (r=.23). The present study found that the commonality of task-relevant and task-irrelevant information, rather than the stimulus novelty of task-irrelevant information, induces the inefficient allocation of attentional resources in AD/HD.