Faces, flowers and football boots: capacity limits in distractor processing.

While visual attention can be attracted by task-irrelevant stimuli, questions remain regarding how many irrelevant items can be processed simultaneously and whether capacity limits are equivalent for all types of stimuli. To explore these issues, participants were required to classify verbal stimuli that were flanked by either one or two response-matching or response-mismatching faces (Expts. 1 and 2) or objects (Expt. 2). The results revealed that when stimulus categorization was sufficient to trigger flanker interference, distractor processing was insensitive to the number of irrelevant stimuli. When, however, stimulus identification was needed to drive flanker interference, distractor processing was attenuated when two task-irrelevant items were presented. The theoretical implications of these findings are considered.