WhH subjectsswitch between two tasks, performance is slower after a taskswitch tht after a task repetition. We report five experimentsshperi thp a large part ofth)I "task-sh5S) costs" cannot be attributed to a control operation, needed to configureth cognitive system for th upcoming task (e.g., Rogers & Monsell, 1995). In all experiments subjects switchs between picture-naming and word-reading. We presented di#erent stimulieithl in just one of th two tasks, or inboth ofth9S ShSI#qH(93 were larger for stimuli presented inboth tasks ths forthH3 presented in only one task, even after more the 100 intervening trials between prime and probe events. We suggest (as proposed by Allport & Wylie, 2000)th0 stimuli acquire associationswith th tasks inwh9E th9 occur.Whu th current task activation is weak, as on aswitch of tasks, stimuli can trigger retrieval of th associated, competing task, provoking larger time costs.

The effects of repeating a task-irrelevant element and inserting intervening trials between the last prime and the probe trial in a negative priming study were compared with a standard prime/probe pair. An associative model based on SAC (e.g. Reder & Schunn, 1996; Schunn, Reder, Nhouyvanisvong, Richards, & Stroffolino, 1997) was able to account for both the decrease in response times across the repeated primes and the increase in response times when the task-irrelevant element became relevant. Introduction Until recently, theories of attention have focused on the object of attention. These theories emphasized the facilitatory "spotlight" at the center of attention, and the remaining areas of visual space were largely ignored (e.g., Broadbent, 1958; Shiffrin & Schneider, 1977). Over the past several years, however, researchers have developed evidence of an inhibitory effect of attention on objects that fall outside the spotlight. In particular, if some part of a visual display...

this article was supported by Grants 1R01 MH52808-01 and 2-R01MH52808 from the National Institute of Mental Health, Grant N0001495 -1-0223 from the Office of Naval Research, Grant SBR-9873465 from the National Science Foundation, and Grant F49620-97-1-0054 from the Air Force Office of Scientific Research

Negative priming refers to the situation where an ignored item on an initial prime trial suffers slowed responding when it becomes the target item on a subsequent probe trial. In this experiment (and a replication), we (matching) governs negative priming.