N-Back as a measure of working memory capacity

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Harrison, Tyler Leland
Engle, Randall W.
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One of the most important findings in cognitive psychology, is the relationship of working memory capacity (WMC) to a host of important cognitive activities, the manner in which WMC interacts with many different cognitive variables, and the consequences for the individual when WMC is reduced due to interventions such as sleep deprivation and psychopathology. However, one often over-looked problem is that researchers use different cognitive tasks to measure and study working memory capacity: differential studies have historically used complex span tasks to assess WMC. However, n-back tasks are often used in neuroimaging studies because the task lends itself to the requirements of fMRI studies. The implicit assumption is that both types of tasks measure the same construct. For the present study, both complex span performance and n-back performance was measured, in 328 subject, to see whether they measured the same construct. The size of the stimulus pool for the n-back tasks was manipulated to determine whether n-back tasks with more interference (i.e., with a smaller stimulus pool) were more strongly correlated with cognitive ability. Additionally, the presence of lure trials was manipulated within the n-back tasks to examine whether the most interfering lures were more strongly correlated with complex span performance. From the data, I argue that complex span tasks and n-back tasks measure different sub-processes of WMC and that this causes the two tasks to load onto separate factors, the number of stimuli that an n-back task uses changes its correlation to other measures of cognitive ability, and that the false alarms to lures closest to n are most strongly correlated with both complex span tasks and fluid intelligence but only for n-back tasks with a small stimulus pool.
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