According to James Swanson et al, ADHD or Attention Deficit Hyperactivity Disorder, whether Inattentive type, Hyperactive type or Combined type, is characterised by difficulties with attention in at least one of three areas, of which executive function is just one. The other two components are ‘alerting’ and ‘orienting’.
Alerting is the ability of the brain to inhibit background neural activity or ‘noise’, thus filtering out extraneous stimuli and allowing the person to pay attention to the stimulus or ‘signal’. Orienting is the ability to shift attention to the signal, directing the brain’s resources to speed up processing of the signal, and eliminating extraneous stimuli. Executive function or control oversees the process and the brain’s responses, directing behaviour towards the task in hand and the achievement of the objective.
Chris Chandler in his book ‘The Science of ADHD‘, describes the symptoms of ADHD in these terms. “Poor sustained attention is thought to be attributed to an alerting deficit…[and] may be evident in ADHD-I subtypes”. “Poor selective attention is a reflection of an orienting deficit…[and may be present] in ADHD-I and ADHD-C”, and “impulsivity is associated with a defect in executive function…in ADHD-H and ADHD-C. Although the distinction between the subtypes is not crystal clear, this theory offers the possibility to test the basis of subtype differences. And furthermore, one or more of the systems may be dysfunctional in any one individual with or without comorbidities.”