An observation on set and visual comparison processes

Tasks involving the comparison of sequentially presented stimulus items to determine identity have generally only required interpretation in terms of simple matching. Some studies have attempted to show effects of selective set in these tasks but with little success except in tasks involving comparison of sentences with pictures. By simplifying the task a reliable set effect is demonstrated, showing that a mismatch of certain stimulus attributes only has an identifiable effect on a subject's reaction-time if he may reasonably be supposed to know that the attribute is critical and is set to examine stimulus items for the attribute. Such conditions result in a relatively fast judgement. The finding suggests that the sequential “same“/“different” judgement is a richer source of data concerning recognition and comparison than has been supposed.