Michelle Simmons and Ira Fischler. Functions of the central executive component of working memory: A dual-task version of the n-back task.
    Working memory is thought of as a cognitive process capable of briefly storing and  manipulating information. Working memory consists of two domain-specific slave systems and a central executive, which is responsible for coordinating this simultaneous storage and manipulation of information and other executive functions. The n-back task is an experimental task that recently has been used to examine the neurophysiological substrates of working memory. In the n-back task, participants are presented with a series of stimuli and are to indicate whether the current stimulus matches the stimulus presented n stimuli back in the series, where n equals a number between 0 and 3. The results of these neuroimaging studies suggest that the n-back requires executive control at higher levels of n, but not at lower levels of n. This hypothesis was tested in 3 experiments in which participants were asked to perform versions of the n-back task concurrent with secondary tasks designed to tax the various component processes of working memory. In Experiment 1, an auditory-verbal n-back was paired with a visual-spatial version of the n -back. Relative to the single-task conditions, the dual-task conditions produced marked interference in the 2- and 3-back tasks, but not in the 0- and 1-back tasks. In Experiment 2, the verbal and spatial n-backs were again paired but the length of time between stimuli was shortened in order to test a time-sharing hypothesis regarding the results of Experiment 1. The accuracy results replicated the results of experiment 1, but the reaction time data showed interference in the 1-, 2-, and 3-back tasks. In Experiment 3, the auditory-verbal n-back was paired with three visual tasks: a rhyme task, a random keypress task, and a mental rotation task. The results from these dual-task pairings indicate that the results from Experiments 1 and 2 may reflect mere difficulty rather than the need for central executive resources specifically. Taken together the results of these experiments lead to the conclusion that the n-back task is a complex task that relies on multiple processes, some of which can be considered executive processes and others that are less executive in nature.