Dissociation of attentional processes in patients with focal frontal and posterior lesions.

A location-based ('select-what, respond-where') priming task was used to examine three measures of selective attention (interference (INT), negative priming (NP), and inhibition of return (IOR)) as a function of focal brain pathology and the complexity of target selection. Control subjects showed different patterns of performance for the three attentional measures as a function of complexity, suggesting some independence among INT, NP, and IOR. Brain-damaged subjects showed significant response slowing, as well as a number of lesion-specific attentional abnormalities. Right frontal (including bifrontal) damage resulted in proportionally increased interference related to task complexity. Left posterior damage increased IOR in the most complex task, while left frontal damage reversed the control pattern of IOR as a function of complexity. Right hemisphere (right posterior and right frontal damage) pathology resulted in a virtual loss of negative priming at all levels of task complexity; left and bifrontal damage resulted in diminished NP only related to increases in the complexity of selection. INT, NP, and IOR are mediated by different brain regions and their expression can be modulated by the complexity of the selection task.