Elsevier

Intelligence

Volume 33, Issue 6, November–December 2005, Pages 623-642
Intelligence

Memory span and general intelligence: A latent-variable approach

https://doi.org/10.1016/j.intell.2005.05.006Get rights and content

Abstract

There are several studies showing that working memory and intelligence are strongly related. However, working memory tasks require simultaneous processing and storage, so the causes of their relationship with intelligence are currently a matter of discussion. The present study examined the simultaneous relationships among short-term memory (STM), working memory (WM), and general intelligence (g). Two hundred and eight participants performed six verbal, quantitative, and spatial STM tasks, six verbal, quantitative, and spatial WM tasks, and eight tests measuring fluid, crystallized, spatial, and quantitative intelligence. Especial care is taken to avoid misrepresenting the relations among the constructs being studied because of specific task variance. Structural equation modelling (SEM) results revealed that (a) WM and g are (almost) isomorphic constructs, (b) the isomorphism vanishes when the storage component of WM is partialed out, and (c) STM and WM (with its storage component partialed out) predict g.

Section snippets

Participants

208 Psychology undergraduates participated in the study to fulfill a course requirement. Their mean age was 20.73 (SD = 3.7).

Administered memory span tasks

Verbal STM was measured by the forward and backward letter span tasks, while quantitative STM was measured by the forward and backward digit span tasks. The selection of those verbal and quantitative STM tasks was made following the study by Engle et al. (1999): “tasks thought to be good STM tasks were simple word span with dissimilar words, simple word span with similar

Results

The descriptive statistics are shown in Table 1. Tasks' correlations and reliability indices (Cronbach's alpha) are also presented in Table 1. The measures meet standard criteria for uni-variate normality with skew values less than 3 and kurtosis values less than 4 (Kline, 1998). Reliability indices show appropriate values. CFA and SEM analyses were conducted using LISREL 8.54 (Jöreskog & Söborn, 2001).

General discussion

The findings show that WM and g are (almost) isomorphic constructs, but this is only supported when the WM latent factor comprises storage-plus-processing requirements. Once the storage component of the WM system is partialed out, the relationship between WM and g reveals much more unstable. Further, the simultaneous analysis of the relationships among STM, WM, and g showed that both STM and WM (with its storage component partialed out) predict g with the same power.

Kane et al. (2004) claimed

Acknowledgement

The research referred to in this article was supported by a grant funded by the Spanish Ministerio de Ciencia y Tecnología (Grant N° BSO2002-01455). We thank Phillip L. Ackerman and Arthur R. Jensen for their helpful comments to a previous version of the present article.

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