Neurophysiological Attention Test (NAT) for Objective Assessment of Attention Deficit Hyperactivity Disorder (ADHD)

Inclusion Criteria: * Specific inclusion criteria for ADHD are: 1. meet established DSM-5 criteria for ADHD predominately inattentive or combined subtype with clinically significant levels of impairment, diagnosed by structured clinical interview, the Mini International Neuropsychiatric Interview, and corroborating information 2. Clinical Global Impression-Severity (CGI-S) score ≥ 4 for ADHD 3. no lifetime history of DSM-5 bipolar disorder, psychotic disorder, pervasive developmental disorder, obsessive-compulsive disorder, substance abuse, or substance dependence (except nicotine) as assessed wit the MINI 4. able in the opinion of the investigator to complete all required study procedures. Exclusion Criteria: * Exclusion criteria for both groups are: 1. History of diagnosis of childhood disorder other than ADHD (e.g. autism, dyslexia) 2. history of any general medical condition likely to require chronic use of medication with identified CNS effects suspected to alter cognitive performance 3. history of seizure disorder, brain tumor, other major neurological disorder or head injury resulting in loss of consciousness 4. serious oxygen deprivation 5. current psychopathology requiring ongoing treatment with antipsychotic medications, mood stabilizers, benzodiazepines, or anticonvulsants 6. current untreated psychopathology which is rated to be primary in terms of severity (greater than ADHD severity) 7. current treatment with guanfacine.