Inhibitory tagging in visual search: only in difficult search are items tagged individually.

Several theories and models of visual search assume that inhibitory tagging of items is used to improve the efficiency of the search process, by discouraging revisits of previously inspected and rejected items. Therefore, search should become less efficient when the search display consists of moving items. In four experiments this hypothesis was tested. In the first two experiments there was no difference between search amongst static and moving items even though motion conditions were blocked (Experiment 1), or displays contained up to 36 items (Experiment 2). However, in Experiments 3 and 4, where the items used in the search display forced the participants to keep track of individual items performance dropped when the items moved. Visual search showed a remarkable robustness against motion, which current theories and models of visual search have difficulties to describe. Taken together, the results reported here indicate that there is a difference between the processes used in easier search and those used in search where items need to be individuated. A framework encompassing these results is proposed.