The cost of visual filtering.

Speeded choice responses (reading or naming) to a relevant stimulus under conditions of spatial uncertainty are delayed by the simultaneous occurrence of other events. This "filtering cost" occurs despite high discriminability of target and distractors, which allows parallel detection of the target in search through the same displays. Reading is also delayed when the removal of irrelevant objects from the field coincides with the onset of the target. Filtering costs are caused by the processing of events rather than by the mere presence of irrelevant items. They are eliminated by advance information about the location of the target or by advance presentation of maintained distractors.