Study of 22 adults diagnosed with ADHD using a manual trial-by-trial Stroop color-word test and a blocked explicitly cued task switching paradigm.

Joseph A King,undefined1 Michael Colla,2 Marcel Brass,1,3 Isabella Heuser,2 and DY von Cramon1 

Abstract


Background

Contemporary neuropsychological models of ADHD implicate impaired cognitive control as contributing to disorder characteristic behavioral deficiencies and excesses; albeit to varying degrees. While the traditional view of ADHD postulates a core deficiency in cognitive control processes, alternative dual-process models emphasize the dynamic interplay of bottom-up driven factors such as activation, arousal, alerting, motivation, reward and temporal processing with top-down cognitive control. However, neuropsychological models of ADHD are child-based and have yet to undergo extensive empirical scrutiny with respect to their application to individuals with persistent symptoms in adulthood. Furthermore, few studies of adult ADHD samples have investigated two central cognitive control processes: interference control and task-set coordination. The current study employed experimental chronometric Stroop and task switching paradigms to investigate the efficiency of processes involved in interference control and task-set coordination in ADHD adults.

Methods

22 adults diagnosed with persistent ADHD (17 males) and 22 matched healthy control subjects performed a manual trial-by-trial Stroop color-word test and a blocked explicitly cued task switching paradigm. Performance differences between neutral and incongruent trials of the Stroop task measured interference control. Task switching paradigm manipulations allowed for measurement of transient task-set updating, sustained task-set maintenance, preparatory mechanisms and interference control. Control analyses tested for the specificity of group × condition interactions.

Results

Abnormal processing of task-irrelevant stimulus features was evident in ADHD group performance on both tasks. ADHD group interference effects on the task switching paradigm were found to be dependent on the time allotted to prepare for an upcoming task. Group differences in sustained task-set maintenance and transient task-set updating were also found to be dependent on experimental manipulation of task preparation processes. With the exception of Stroop task error rates, all analyses revealed generally slower and less accurate ADHD group response patterns.

Conclusion

The current data obtained with experimental paradigms deliver novel evidence of inefficient interference control and task-set coordination in adults with persistent ADHD. However, all group differences observed in these central cognitive control processes were found to be partially dependent on atypical ADHD group task preparation mechanisms and/or response inconsistency. These deficiences may have contributed not only to inefficient cognitive control, but also generally slower and less accurate ADHD group performance. Given the inability to dissociate these impairments with the current data, it remains inconclusive as to whether ineffecient cognitive control in the clinical sample was due to top-down failure or bottom-up engagement thereof. To clarify this issue, future neuropsychological investigations are encouraged to employ tasks with significantly more trials and direct manipulations of bottom-up mechanisms with larger samples.


Additional resources on this topic:


1. Max Planck Institute for Human Cognitive and Brain Sciences, Department of Cognitive Neurology, Stephanstr. 1A, D-04103 Leipzig, Germany

2. Charité-Universitätsmedizin Berlin, Campus Benjamin Franklin, Department of Psychiatry and Psychotherapy, Eschenallee 3, D-14050 Berlin, Germany

3. Ghent University, Department of Experimental Psychology, Henri Dunantlaan 2, BE-9000 Ghent, Belgium

undefinedCorresponding author.

Joseph A King: king@cbs.mpg.de; Michael Colla: michael.colla@charite.de; Marcel Brass: marcel.brass@ugent.be; Isabella Heuser: katharina.schmalfeld@charite.de; DY von Cramon: mittag@cbs.mpg.de

Behav Brain Funct. 2007; 3: 42. Published online 2007 August 20. doi: 10.1186/1744-9081-3-42. PMCID: PMC1988818 Copyright © 2007 King et al; licensee BioMed Central Ltd.

Received January 23, 2007; Accepted August 20, 2007.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.