Identifying the source of dual-task costs by manipulating stimulus-action effect compatibility

Why do you do what you do? Except for emotional and reflexive behaviors, humans usually act in order to produce certain effects or outcomes: may it be to shoot a basketball or write a paper. In any instance, a particular action has to be determined that will produce the desired outcome. In dual-task (i.e., multitasking) situations, humans perform multiple actions, and thus, multiple outcomes are present. For example, when driving while talking, an individual’s actions produce multiple outcomes, including changes in car position and changes in conversation topics. In this dissertation, I explored the idea that outcomes may be a key determinant in one’s ability to coordinate multiple actions. In a series of experiments, I designed tasks in which actions were followed by experimentally-induced outcomes (e.g., a light that consistently follows a response). To first test whether outcomes are involved in dual-task coordination, I examined whether the compatibility between stimuli and outcomes could explain a well-established finding in the dual-task literature: that the particular pairings of tasks influence the magnitude of dual-task costs (performance differences between performing two tasks versus one). Dual-task costs were reduced when stimuli and outcomes were compatible within a task compared to between tasks. Follow-up experiments were conducted to determine the most likely source of dual-task costs. Together, these results provide evidence that the cognitive processes engaged during dual-tasking operate on outcome representations, which may have real-world implications as they suggest that adding the appropriate outcomes can reduce dual-task interference.