Academic journal article Cognitive, Affective and Behavioral Neuroscience

Capacity Estimates in Working Memory: Reliability and Interrelationships among Tasks

Academic journal article Cognitive, Affective and Behavioral Neuroscience

Capacity Estimates in Working Memory: Reliability and Interrelationships among Tasks

Article excerpt

Abstract The concept of capacity has become increasingly important in discussions of working memory (WM), in so far as most models of WM conceptualize it as a limited-capacity mechanism for maintaining information in an active state, and as capacity estimates from at least one type of WM task- complex span-are valid predictors of real-world cognitive performance. However, the term capacity is also often used in the context of a distinct set of WM tasks, change detection, and may or may not refer to the same cognitive capability. We here develop maximum-likelihood models of capacity from each of these tasks-as well as from a third WM task that places heavy demands on cognitive control, the self-ordered WM task (SOT)-and show that the capacity estimates from change detection and complex span tasks are not correlated with each other, although capacity estimates from change detection tasks do correlate with those from the SOT. Furthermore, exploratory factor analysis confirmed that performance on the SOT and change detection load on the same factor, with performance on our complex span task loading on its own factor. These findings suggest that at least two distinct cognitive capabilities underlie the concept of WM capacity as it applies to each of these three tasks.

Keywords Workingmemory . Short-termmemory . Cognitive control

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One of the hallmarks of Edward E. Smith's approach to scientific problems was an eagerness to use all available tools to constrain hypotheses and distinguish between alternative explanations of the data. In our many discussions of human working memory (WM), he was always struck with the elegance and utility of the simple mathematical model of WM capacity used in the literature on change detection tasks (Cowan, 2001;Pashler,1988), and as we progressed in our research into WM deficits in patients with schizophrenia at the end of his career (Smith & Van Snellenberg, 2011;Van Snellenberg, Girgis, et al., 2013; Van Snellenberg, Wager, Abi-Dargham, Urban, & Smith, 2010), he was eager to develop a similar capacity model for the task that we were using to probe these deficits, the self-ordered working memory task (SOT). A critical question was whether the ability to hold items in memory during performance of the SOT, a highdemand WM task requiring substantial cognitive control, was related to the relatively pure measure of the number of items that an individual can hold in visual short-term memory that is provided by WM capacity estimates from change detection tasks.

At the core of this question is a broader one about the cognitive processes that underlie various WM tasks. For example, abundant evidence points to a capacity limit in humans of approximately four items that can be concurrently held in WM, which is thought to be tapped relatively directly by canonical change detection tasks (Cowan, 2001;Lin& Luck, 2012; Luck & Vogel, 1997; Vogel & Machizawa, 2004). It is natural to ask whether this capacity limit constrains performance on WM tasks other than change detection tasks, especially those that are more complex and impose additional demands on cognitive control. One type of WM task that requires substantial cognitive control, known as complex span tasks, can also provide an estimate of WM capacity (or span), but psychometric studies have indicated that capacity estimates from these tasks are distinct from the estimates from change detection tasks; they load on separate factors, and they exhibit different patterns of predictive validity, particularly with respect to measures of fluid intelligence (Conway, Cowan, Bunting, Therriault, & Minkoff, 2002; Cowan et al., 2005; Shipstead, Redick, Hicks, & Engle, 2012). Thus, the existing literature on complex span and change detection tasks suggests that at least two distinct sets of cognitive processes are tapped by different classes of putative WM tasks, and it remains an open question whether the types of high-demand WM tasks used to tap cognitive control processes load on the same underlying cognitive capabilities required for successful performance of complex span tasks, as well as whether these tasks are constrained by the WM capacity limits tapped by change detection tasks. …

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