Endogenous switch costs occur within task sequences at substructural boundaries

Task switching studies to date have used simple, single step tasks. Two experiments show that switch costs can also be found when participants are asked to switch between complex tasks that consist of four subtasks, where each subtask requires participants to respond to one of eight binary dimensions of a compound stimulus. In Experiment 1, a large switch cost is found for the first subtask, with little or no switch cost on subsequent subtasks, except for a subtask that could indicate chunking of subtasks into a substructure. In experiment 2 the large switch cost for the first subtask is replicated, and small switch costs are observed for the first and final subtasks in task chunks, corresponding to substructural boundaries. It is concluded that these small switch costs reflect endogenous processes concerned with instantiation of task chunks as subtasks.