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Abstract:
Attention deficit/ hyperactivity disorder (ADHD) is
characterised by impulsivity, inattentiveness and, sometimes,
hyperactivity. It has been argued that the impulsivity of children
with ADHD reflects a deficient inhibitory control system.
Impulsivity has also been shown in ADHD adults in an anti-saccade
task: they are less able to inhibit a reflexive saccade to an
eccentric visual target before correctly looking in the opposite
direction (Munoz et al., 1998). We used a stop-signal paradigm to
examine inhibitory control in adults with ADHD and their
age-matched controls. Participants viewed a central fixation spot
and looked to an eccentric target upon its appearance and the
disappearance of the fixation spot (GO trial). A signal to stop,
indicated by the return of the central spot, occurred rarely (25%
of trials) and at variable delays after the appearance of the
target (STOP trial). We measured accuracy on STOP trials and
saccadic reaction time (SRT) on GO trials and incorrect STOP
trials. Although ADHD adults had slower SRTs for both GO and STOP
trials, their STOP-trial error rate did not differ from controls.
Nonetheless, the inhibitory control function which takes into
account the speed/ accuracy trade-off was similar across the
groups. We conclude that (1), the inhibitory control function does
not accurately reflect differences in processing, or (2), ADHD
adults, unlike children with ADHD, are able to adapt to task
demands.
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