“…It is likely that different executive processes are implemented by separate, albeit interactive, frontal areas (Stuss, Shallice, Alexander, & Picton, 1995;Umiltà & Stablum, 1998; but see Duncan, 1995). Impairments of the executive system have been reported in a variety of normal and pathological states that involve the frontal lobes, including aging (West, 1996), traumatic brain injury (Strum, Willmes, Orgass, & Hartje, 1997), frontal strokes (Duncan, 1986), dementias (Parasuraman & Greenwood, 1998), schizophrenia (Frith, 1992), and attention deficit disorder (Barkley, 1998). Disruptions of corticostriatal loops, such as those evidenced in Parkinson's disease, also lead to deficits in executive processes (Hayes, Davidson, Keele, & Rafal, 1998).…”