When individuals are confronted with multiple task demands, control processes are assumed to govern and coordinate the potentially conflicting cognitive operations.  Evidence for these control processes are found in a phenomenon called sequential effects: After a trial with high conflict, the effects of conflict are smaller than after a trial with little conflict.  That is, conflict causes individuals to pay less attention to the irrelevant information, thereby reducing its consequences.  This pattern is presumed to reflect the dynamic allocation of control, and we exploited it to probe the structure of task representations.  We used a conflict task called the Simon task, in which a task-relevant stimulus is presented in different locations that correspond with the locations of the appropriate responses.  However, its location must be ignored, because the identity of the stimulus, not its location, indicates the appropriate response.  First, we established that sequential effects in the Simon task occur even when neither the stimulus identity nor the stimulus location are the same as on the previous trial (Akcay & Hazeltine, 2007).  This finding indicates that sequential effects do not stem from the inhibition of specific-stimulus features but instead relate to high level representations.

We next examined the boundary conditions of sequential effects to examine task representations.  When we encouraged participants to think of a version of the Simon task as two separate tasks, sequential effects were not observed after a task switch.  Moreover, when the participants switched back to a task, the congruency of the last trial of that task affected the magnitude of the congruency effect on the current trial (Akcay & Hazeltine, 2008).  These findings suggest that sequential effects relate to representations of the task and not simply attentional states.  As with the findings from the dual-task studies, the results indicate that tasks are represented as more than just a collection of stimulus-response associations.  The brain appears to encode rich representations of the task and these representations have important effects on performance in terms of compatibility effects, learning, and control processes (Hazeltine et al., 2011). 

Representative Papers

• Hazeltine, E., Lightman, E., Schwarb, H., & Schumacher, E. H. (2011). The boundaries of sequential modulations: Evidence for set-level control. Journal of Experimental Psychology: Human Perception and Performance, 37, 1898-1914.
• Akcay, C. & Hazeltine, E. (2011). Domain-specific conflict adaptation without feature repetitions. Psychonomic Bulletin & Review, 18, 505-511.
• Hazeltine, E., Akcay, C., & Mordkoff, J. T. (2011). Keeping Simon simple: Examining the relationship between sequential modulations and feature repetitions with two stimuli, two locations and two responses. Acta Psychologica, 136, 245-252.
• Akcay, C. & Hazeltine, E. (2008). Feature-overlap and conflict monitoring: Two sources of sequential modulations. Journal of Experimental Psychology: Human Perception and Performance, 34, 958-973.