Several theoretical models suggest that the core deficit in children with Attention
Deficit Hyperactivity Disorder (ADHD) relies on response inhibition. However, research concerning the persistence of this deficit in adulthood is lacking.

This has been studied by comparing performances obtained by adults with
ADHD and control subjects in a Simon Reaction Time (RT) task. The inhibition of
inappropriate responses elicited by irrelevant information was evaluated through
1/ the analysis of RT and accuracy distribution ( slope of the delta plots) and 2/ the
analysis of electromyographic activity (EMG), which provided the possibility to identify
partial errors (subthreshold EMG burst associated with incorrect response and
preceding the correct one).

The classic analysis of mean RT indicated a larger Simon effect in adults with ADHD
suggesting difficulties in inhibiting the automatic activation produced by the non relevant stimulus. However, in contrast, distribution analyses as well as analysis of partial errors revealed that the ability to suppress the automatic response remains
intact in these patients.