Endogenous and exogenous attention in patients with conversion paresis

Endogenous and exogenous attention of patients with conversion paresis was investigated using Posner's 'covert orienting of visual attention' task. In the light of previous evidence showing that inhibition of higher-level control functions plays a role in conversion paralysis (e.g., Marshall, Halligan, Fink, Wade, & Frackowiak, 1997), patients were expected to display weaker cue effects in the endogenous condition and weaker inhibition of return (IOR) in the exogenous condition. Eight patients with conversion paresis in one or more limbs and eight healthy controls were administered the attention task in a verbal response condition and in a limb response condition in which subjects responded with each limb separately. When responding verbally, patients showed relatively weakened endogenous cue effects on a 150-ms stimulus onset asynchronicity (SOA) and no IOR in the exogenous condition. Comparable effects emerged when patients responded with affected limbs but not when they responded with unaffected limbs. The findings suggest impairment in voluntary attention. High-level inhibition is suggested to interfere with the orientation to stimuli that prime responses with affected limbs. The fact that similar results were found for verbal responses is interpreted as supporting the view that attention deficits are manifested on a high, abstract level of cognitive processing.