Elsevier

Intelligence

Volume 38, Issue 6, November–December 2010, Pages 552-561
Intelligence

Working memory and fluid intelligence in young children

https://doi.org/10.1016/j.intell.2010.07.003Get rights and content

Abstract

The present study investigates how working memory and fluid intelligence are related in young children and how these links develop over time. The major aim is to determine which aspect of the working memory system—short-term storage or cognitive control—drives the relationship with fluid intelligence. A sample of 119 children was followed from kindergarten to second grade and completed multiple assessments of working memory, short-term memory, and fluid intelligence. The data showed that working memory, short-term memory, and fluid intelligence were highly related but separate constructs in young children. The results further showed that when the common variance between working memory and short-term memory was controlled, the residual working memory factor manifested significant links with fluid intelligence whereas the residual short-term memory factor did not. These findings suggest that in young children cognitive control mechanisms rather than the storage component of working memory span tasks are the source of their link with fluid intelligence.

Introduction

In recent years there has been substantial evidence that fluid intelligence and working memory are closely related (Colom et al., 2003, Conway et al., 2002, Cowan et al., 2005, Engle et al., 1999, Kane et al., 2004, Oberauer et al., 2005, Unsworth et al., 2009). Although researchers generally agree on the existence of such a relationship, the underlying nature of the association remains an issue of controversy. Furthermore, the vast majority of studies have focused on adults, and it remains to be seen whether the findings extend to children. The main aim of the present study was to explore the development of working memory and fluid intelligence in a population of young children in order to clarify the relationship between these two aspects of fluid cognition.

Fluid intelligence (Gf) is a complex cognitive ability that allows humans to flexibly adapt their thinking to new problems or situations. The concept has been defined by Cattell (1971) as: “an expression of the level of complexity of relationships which an individual can perceive and act upon when he does not have recourse to answers to such complex issues already sorted in memory” (Cattell, 1971, p. 99). In other words, Gf can be thought of as the ability to reason under novel conditions and stands in contrast to performance based on learned knowledge and skills or crystallized intelligence (Haavisto and Lehto, 2005, Horn and Cattell, 1967). Gf is generally assessed by tasks that are nonverbal and relatively culture-free.

Working memory (WM) has been described as a system for holding and manipulating information over brief periods of time, in the course of ongoing cognitive activities. Most theorists in the field agree that WM comprises mechanisms devoted to the maintenance of information over a short period of time, also referred to as short-term memory (STM), and processes responsible for cognitive control that regulate and coordinate those maintenance operations (Baddeley, 2000, Cowan et al., 2005, Engle, 2010, Engle et al., 1999, Engle et al., 1999). WM is often assessed by complex span tasks that involve the simultaneous processing and storage of information (Daneman & Carpenter, 1980). An example of such a task is counting span, in which participants are asked to count a particular class of items in successive arrays and to store at the same time the number of target items in each array (Case, Kurland, & Goldberg, 1982). These complex span measures stand in contrast to simple span tasks that require only the storage of information with no explicit concurrent processing task. A typical simple span task is digit span, requiring the immediate recall of lists of digits.

Although STM and WM are theoretically distinct and sometimes separately assessed, no single task is a pure measure of either construct (Conway et al., 2002, Conway et al., 2008, Engle et al., 1999). Even a seemingly simple task such as digit span is likely to involve cognitive control mechanisms. In a recent study, Unsworth and Engle (2006) showed that a simple span task with long lists of item taps the same controlled retrieval mechanism as complex span tasks. The authors argue that items from the end of a long list are retrieved from a capacity-limited STM store (or primary memory), whereas items from the beginning of the list which have been displaced from the limited capacity STM store are retrieved via a controlled search of secondary memory. Also, complex span tasks rely on simple storage as well as cognitive control mechanisms (Bayliss et al., 2003, La Pointe and Engle, 1990). Thus, simple and complex span tasks are likely to tap both storage and cognitive control, to differing degrees: whereas complex span tasks primarily reflect cognitive control and secondary storage, simple span measures are most sensitive to storage and depend less on cognitive control (Conway et al., in preparation, Kane et al., 2004, Unsworth and Engle, 2006).

The balance of these contributions to simple and complex span tasks may change with development. The efficiency of processing improves as children get older (Case et al., 1982); simple span tasks might therefore rely more heavily on cognitive control processes in younger than in older children or in adults (Engle, Tuholski, et al., 1999). If this is the case, simple and complex span tasks should be more closely associated in children than in adults, due to the common contribution of cognitive control mechanisms. Consistent with this position, Hutton and Towse (2001) found that simple and complex span tasks loaded on the same factor in 8- and 11-year-olds. In contrast, other studies suggest that simple and complex span tasks tap distinct but associated underlying constructs in developmental populations (Alloway et al., 2006, Alloway et al., 2004, Gathercole et al., 2004, Kail and Hall, 2001, Swanson, 2008).

Many studies have shown that in adults, Gf and WM are strongly linked (Colom et al., 2003, Conway et al., 2002, Cowan et al., 2005, Engle et al., 1999, Kane et al., 2004). The underlying nature of the association is, however, not fully understood. According to Engle, WM and Gf both rely on attentional control mechanisms (Engle 2010). In Gf tasks cognitive control is required to analyze problems, monitor the performance process, and adapt the resolution strategy as performance proceeds. In a similar way, cognitive control might be needed in WM tasks in order to maintain memory representations in an active state in the face of interference. A theoretically different account of the Gf–WM link has been proposed by Colom, Abad, Quiroga, Shih and Flores-Mendoza (2008). They argue that STM storage rather than cognitive control accounts for the relationship between WM and Gf.

Supporting evidence for both positions exists. In a latent variable study, Engle, Tuholski, et al. (1999) have shown that when the common STM and WM variance was removed, the WM residual factor was related to Gf, whereas the STM residual was not. Conway et al., 2002, Kane et al., 2004 reported similar findings, indicating that the cognitive control demands rather than the storage component of WM span tasks are the source of the link with Gf. In contrast, Colom and colleagues have consistently found that individual differences in Gf are significantly associated with both STM and WM (Colom et al., 2005, Colom et al., 2006, Colom et al., 2008). In some of these studies STM was identified as a stronger predictor of Gf than WM, providing support to their position that short-term storage and not cognitive control mechanisms is responsible for the link between WM and Gf. One explanation of the discrepancies across these and other studies is that the degree to which STM and WM appear to be correlated or distinct depends on the particular tasks employed. The use of different tasks by different research groups therefore confounds direct comparisons of results.

The relationship between WM and Gf in children has been less intensively investigated (see Fry & Hale, 2000 for a review), and the few studies that exist generally agree that WM and Gf are strongly related but distinct constructs (Alloway et al., 2004, Fry and Hale, 2000). However, most of these studies do not address whether WM as a short-term storage system or as a cognitive controlling device is making significant contributions to children's fluid intelligence. In a recent latent variable study on 6- to 9-year-olds, Swanson (2008) found that when controlling for the correlations between WM and STM, the residual WM factor, but not STM, predicted Gf. A similar result was obtained by Bayliss, Jarrold, Baddeley, Gunn, and Leigh (2005). Importantly, in contrast to Swanson (2008), not only WM but also STM accounted for unique variance in Gf (see also Tillman, Nyberg, & Bohlin, 2008). In another developmental study the WM residual factor failed however to manifest significant links with Gf (Bayliss et al., 2003).

The purpose of the present study was to explore the underlying nature of the relationship between WM, STM, and Gf in 5- to 9-year-old children. The study had two major aims: first, it explored whether simple and complex span tasks are more closely associated in younger children than in older children or in adults, potentially because of the contribution of cognitive control mechanisms in assessments of STM in younger children (Engle et al., 1999, Hutton and Towse, 2001). Second, the study investigated whether the pattern of results favors either the proposal that cognitive control is driving the link between complex span tasks and Gf (Engle and Kane, 2004, Kane and Engle, 2002), or that STM accounts for the relationship between complex span tasks and Gf (Colom et al., 2006). The study is unique in using a latent variable approach to estimate the relationships of WM and STM with Gf in young children followed longitudinally over three years. As complex and simple span tasks have been suggested to reflect both storage and cognitive control to differing degrees, unique relationships of WM and STM with Gf were explored in order to disentangle the specific effects of cognitive control and short-term storage to Gf.

WM and STM were assessed by multiple measures that are widely used in research with children and that are part of many standardized test batteries (e.g., AWMA, Alloway, 2007; CNRep, Gathercole & Baddeley, 1996; WMTB-C, Pickering & Gathercole, 2001). WM was evaluated by two complex span tasks in which recall was verbal and the nature of the processing activity was either verbal (backwards digit recall) or visuo-spatial (counting recall). STM was assessed by two storage-only tasks: digit recall and nonword repetition. Both tasks involve spoken presentation of the stimuli; the to-be-remembered material differed however in terms of content domain and familiarity. Gf was evaluated by the Raven's Colored Progressive Matrices Test (CPM; Raven, Court, & Raven, 1986) a visuo-spatial reasoning and problem solving task in which children need to derive a set of rules or relations between stimuli in order to complete a visual pattern. To complete an item, a number of subresults have to be stored during the period that the item is being solved. The more difficult problems entail a larger number or more difficult rules and more figural elements per entry (see Carpenter, Just, & Shell, 1990 for a review). The Raven's Matrices tests is one of the most commonly adopted means of testing Gf in both adults (Carpenter et al., 1990, Conway et al., 2002, Engle, 2010) and in children (Bayliss et al., 2003, Swanson, 2008), and loads highly on a general factor in psychometric studies of intelligence (Carroll, 1993).

In summary, the presented study investigates the underlying factor structure of the above presented measures in a population of young children in order to explore (a) if WM, STM, and Gf represent dissociable constructs in young children and (b) how these different aspects of fluid cognition are related and develop over time in an attempt to determine more precisely if a link between WM and Raven's Matrices performance exists in young children and whether the possible association is mediated by short-term storage or cognitive control.

Section snippets

Participants

The initial sample consisted of 122 children from 38 kindergarten classes (11 public schools) in Luxembourg. By careful follow-up and tracking of children who had moved within the country, 119 children were retained from the original sample for the three-year duration of the study. Of the 119 children for whom complete data were available, 61 were boys and 58 were girls. Luxembourgish was the first language for the totality of the participants. All of the children learned German and French as

Preliminary data analysis

All variables were examined separately for each of the three study waves. Skew and kurtosis for all the variables met criteria for univariate normality (see Kline, 2005). Univariate outliers on each of the 15 variables were defined as values more than 3 SD above or below the group mean (Kline, 2005). Four cases, out of the 1785 in the data set met this criterion and were replaced with scores corresponding to plus or minus 3 SD as appropriate. The data manifested reasonable multivariate

Discussion

The main objective of the present paper was to examine the links between WM, STM, and fluid intelligence in a population of young children followed from kindergarten through second grade. A particular focus of the study was to explore whether significant links between WM and fluid intelligence would emerge and more specifically, which aspect of the WM system—short-term storage or cognitive control—might mediate the relationship.

The data indicate that STM and WM performance reflect

Acknowledgements

This project was funded by the Economic and Social Research Council (ESRC) of Great Britain and the Fond National de la Recherche (FNR) of Luxembourg. The authors wish to thank the schools, parents, and children who consented to participate in this study and Christiane Bourg for assistance on task scoring.

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