Covert Orienting of Visual Spatial Attention in Attention Deficit Hyperactivity Disorder: Does Comorbidity Make a Difference?

Archives of Clinical Neuropsychology, Vol. 14, No. 2, pp. 179–189, 1999 Copyright © 1999 National Academy of Neuropsychology Printed in the USA. All rights reserved. 0887-6177/99 $–see front matter PII S0887-6177(97)00097-8 Covert Orienting of Visual Spatial Attention in Attention Deficit Hyperactivity Disorder: Does Comorbidity Make a Difference? Catherine Wood La Trobe University Paul Maruff Mental Health Research Institute of Victoria Swinburne University of Technology Florence Levy Prince of Wales Children’s Hospital Maree Farrow Swinburne University of Technology David Hay Curtin University Attentional performance in children with attention deficit hyperactivity disorder (ADHD) with and without comorbid disorders was examined using the Covert Orienting of Visuospatial Attention Task (COVAT) and the Continuous Performance Task (CPT). The relationship between these two tasks was also examined. The results showed no overall differences on the attention tasks between children with ADHD alone and those with ADHD plus other disorders. Compared to non-ADHD control children, children with ADHD showed a deficit in the disengage operation of covert visuospatial attention, suggesting a difficulty in the endogenous mode of orienting. The ADHD children also showed a general performance deficit on the CPT. Although there was a general slowing on both attention tasks in the ADHD group, there was no relationship between invalid cue effect sizes on the COVAT and the CPT measures. These results indicate that these two attention tasks may be tapping both similar and independent underlying cognitive processes in ADHD. © 1999 National Academy of Neuropsychology. Published by Elsevier Science Ltd This study was supported by a grant from the Government Employees Medical Research Fund and by the National Health and Medical Research Council (Australia). The authors are grateful to the Australian NHMRC Twin Registry and participating families. Address correspondence to: Catherine Wood, School of Psychological Science, La Trobe University, Bundoora, Victoria 3083, Australia; E-mail: 179 180 C. Wood et al. Deficits in attentional processes have been recognised as a core feature of attention deficit hyperactivity disorder (ADHD) for many years (Barkley & Grodzinsky, 1994). However, the underlying nature and pathophysiological significance of the attentional dysfunction in ADHD remain unclear (Pennington & Ozonoff, 1996). Although recent studies have highlighted the role of the frontal lobes and basal ganglia (see Benson, 1991; Levy, 1992; Seidman et al., 1995), the precise relationships between fronto-striatal deficits and symptoms of inattention in ADHD are poorly characterised (Benson, 1991; Pennington & Ozonoff, 1996). Studies of cognitive function in ADHD have focused on different aspects of attentional processing in affected children. Much of the research has been on sustained attention as measured by the Continuous Performance Task (CPT) or one of its variants. This research has supported a general performance deficit in ADHD children that may be independent of, or in addition to, a sustained attention deficit (e.g., Chee, Logan, Schachar, Lindsay, & Wachsmuth, 1989; Harper & Ottinger, 1992; Hooks, Milich, & Lorch, 1994). There is ongoing debate over the interpretation of performance deficits on the CPT in children with ADHD (for a review, see Ballard, 1996). Central to this debate is the lack of established models to guide interpretation of CPT performance within a brain-behaviour framework (Allport, 1988; Maruff & Currie, 1996). Despite the common finding of psychiatric comorbidity in children with ADHD, many studies examining the nature of the attentional dysfunction have not assessed or controlled for comorbid symptoms and/or diagnoses. In a recent study, Fischer, Newby, and Gordon (1995) found that clinic-referred ADHD children who performed “normally” on the CPT performed better on other measures of attention than children with “abnormal” CPT scores. These children were also rated by teachers as less inattentive, by parents as having more conduct and psychosomatic problems, and were less likely to respond to stimulant medication. The effects of comorbidity on attentional processing may be specific to the CPT. Seidman et al. (1995) found similar performance deficits on a variety of executive function tasks (e.g., Wisconsin Card Sorting Test, Stroop Test) in ADHD children with and without comorbid diagnoses of depression, anxiety, and/or conduct disorders. The impaired performance of both groups suggests that the neuropsychological deficits reported were associated with the ADHD symptoms rather than with the comorbid diagnoses. However, tasks thought to measure executive functions in children are factorially complex, and poor performance is not necessarily indicative of frontal lobe impairment (Fletcher, 1996). To better understand attentional function in children with ADHD, it is essential that the tasks used are based on well developed and theoretically valid models of attention. The Covert Orienting of Visuospatial Attention Task (COVAT) described initially by Posner (1980) provides a valid and reliable measure of an individual’s ability to direct visuospatial attention to different areas of the visual field without accompanying eye movements. Primate and human studies suggest that normal performance on the COVAT reflects the integrity of a distributed neural network for directed attention (Corbetta, Miezin, Shulman, & Petersen, 1993; Robinson & Kertzman, 1995). Different cognitive operations (e.g., disengage, move) are thought to be controlled by different nodes of this network. Moreover, the pattern of COVAT performance in both monkeys and humans with predominantly subcortical lesions differs qualitatively from the pattern caused by focal or diffuse cortical damage (Colby, 1991). At least three studies have examined covert visual attention in ADHD. Swanson et al. (1991) found ADHD children with a mixed profile of aggressive/defiant behaviours to have difficulty controlling covert attention over 800-msec intervals when targets ap- ADHD and Comorbid Conditions 181 peared in the right visual field following cues presented to the left visual field. The ADHD group performed normally at 100-msec intervals for both visual fields. Similar results were found by Carter, Krener, Chaderjian, Northcutt, and Wolfe (1995) in a study that excluded participants with ADHD and comorbid mood or anxiety disorders. The findings from these two studies suggested that ADHD is associated with disruption to frontal and striatal attentional areas. Using a COVAT with a choice reaction-time procedure, Pearson, Yaffee, Loveland, and Norton (1995) also found that children with ADHD (with and without comorbid symptoms) performed normally when the time between the cue and target was short but became less reliable as this interval was extended to 300 msec. The unreliability at 300 msec was (...truncated)