This study assessed two relevant aspects of executive
dysfunction in children with either Tourette syndrome (TS)
or ADHD. Process variables derived from existing neuropsychological
measures were used to clarify the executive function construct.
Clustering of responses on measures of verbal fluency,
figural fluency, and verbal learning was examined to assess
strategic response organization. Rule breaks, intrusions,
and repetition errors were recorded to assess inhibition
errors. No significant differences were found among the
three groups (TS, ADHD, and controls) on tasks of response
organization (clustering). In our sample, both the ADHD
and the TS groups were largely free from executive function
impairment, and their performance on the fluency and list
learning tasks was in the average range. There was a significant
group difference on one of the disinhibition variables,
with both TS and ADHD groups showing significantly more
intrusions on verbal list learning trials than controls.
When more traditional total score variables were analyzed
among the three groups, there were no significant differences;
however, analysis of effect size revealed medium-to-large
effect sizes for Letter Word Fluency total score differences
(ADHD vs. controls), and for Semantic Word Fluency
total score differences (ADHD vs. TS), with the
ADHD group having weaker performance in both comparisons.
Results provide some support for the use and analysis of
process variables—particularly those related to inhibition
and intrusion errors, in addition to the total score variables
when assessing executive function deficits in children
with ADHD and TS. While group differences may be found,
children with uncomplicated TS should not routinely be
considered to have significant executive function impairments,
and when deficits are found, they may be attributable to
other comorbid disorders. (JINS, 2001, 7,
102–111.)
