The impact of task rules on distracter processing: automatic categorization of irrelevant stimuli

The goal of the study was to investigate whether task rules are automatically applied to irrelevant distracters. In three experiments, subjects categorized target words which were superimposed on distracter pictures. The categorization rule was arbitrary and the distracters were not relevant at any point during the experiment. We found congruency effects for distracters that belonged to the task-relevant categories, but were never presented as target words. Responses were faster when target and distracter belonged to the same category, i.e., were mapped to the same response, than when they were mapped to different responses. Since the distracters were never responded to in the course of the experiment, interference caused by retrieval of S-R episodes cannot explain the results. Instead, we propose that even arbitrary categorization rules are applied to all suitable stimuli, including distracters. Results are taken as evidence that a currently relevant task rule enhances processing of target-related information thereby increasing interference by task related, but currently irrelevant information.