An examination of vigilance and behavior inhibition deficits related to attention-deficit/hyperactivity disorder inattentive and combined types

Despite the enormous volume of Attention Deficit/Hyperactivity Disorder (ADHD) literature, questions regarding this disorder remain. Currently ADHD children fall into one of several categories, the most common two being: (1) ADHD-Inattentive Type (IA) and (2) ADHD-Combined Type (American Psychiatric Association, 1994). However, researchers have typically treated these groups as a single homogenous population, or focused on the ADHD-Combined Type, largely ignoring the ADHD-IA group. The goal of the current study was to examine the differences in visual orienting and behavior inhibition between these two groups. Specifically, this study examined three current theoretical models, including a vigilance deficit model and an orienting deficit model for the ADHD-Inattentive classification and a Behavior Inhibition Deficit model for the ADHD-Combined type.; Three experimental tasks were administered to 71 male participants, (ages 8 to 10), including 12 ADHD-IA, 34 ADHD-Combined, and 25 controls. Posner's exogenous Visual Orienting Task (VOT) was used to examine orienting deficits, Logan and Cowan's Stop Task was employed to examine behavior inhibition deficits, and the AX version of the Continuous Performance Task (CPT) was used to examine sustained attention deficits. In order to examine vigilance problems, each task included a manipulation of the duration of time the participants awaited stimuli (SOA). The ADHD-IA participants displayed little evidence of general orienting deficits on the VOT, and no evidence of left-visual-field neglect. Rather, they demonstrated problems shifting their visual attention only when the demands on their vigilance abilities were increased. These individuals exhibited no vigilance-related problems on either the Stop Task or CPT, suggesting that their vigilance deficits may be related to remaining alert for peripheral information. Although the ADHD-Combined participants had difficulties with responding appropriately during both the Stop Task and the CPT, these problems did not seem to be isolated to inhibitory responses. Rather, they responded more slowly to stimuli in general on all three tasks. The quite distinct patterns of performance for the two ADHD groups on the three tasks reinforces the need for researchers and clinicians to stop treating these qualitatively different populations as a unitary group and to address the specific deficits associated with each subtype.