Dissociations within the anterior attentional system: effects of task complexity and irrelevant information on reaction time speed and accuracy.

Patients with focal frontal or nonfrontal lesions were compared with control participants on 4 reaction time (RT) tasks varying in levels of complexity based on a feature-integration model of detection. Superior medial lesions affected simple RT speed. Increasing the demands of feature detection did not differentially affect speed of correct responses among the groups. Frontal structures appear to play little role in correct integration of features during detection. The analysis of error types within the complex task revealed a frontal lobe hemispheric distinction between sensitivity and bias: right dorsolateral-decreased sensitivity; left dorsolateral-altered response bias. The frontal lobes, particularly right dorsolateral, were required to inhibit an incorrect response. There are at least 3 functionally and anatomically separable anterior attentional processes.