Order information in multiple-element comparison.

Although it is possible to specify the elements of a list without regard to the order in which they appear, the same distinction may not be possible when the elements are retrieved from memory. To investigate this issue, we used a recognition task in which two strings of letters are presented sequentially. Subjects were instructed to respond "Same" if the second string contained the same elements as the first, regardless of their position, and to respond "Different" otherwise. Despite the fact that order information is irrelevant in this task, we observed in two experiments that reaction time for Same-item trials increased with the number of positions that the letters were displaced. Neither familiarity of the first string nor the delay between strings changed in the size of this displacement effect. To account for this finding, we propose a model in which comparison time for a given letter pair increases with the position difference of the elements in their respective strings.