Abstract
Numerous studies reported a strong link between working memory capacity (WMC) and fluid intelligence (Gf), although views differ in respect to how close these two constructs are related to each other. In the present study, we used a WMC task with five levels of task demands to assess the relationship between WMC and Gf by means of a new methodological approach referred to as fixed-links modeling. Fixed-links models belong to the family of confirmatory factor analysis (CFA) and are of particular interest for experimental, repeated-measures designs. With this technique, processes systematically varying across task conditions can be disentangled from processes unaffected by the experimental manipulation. Proceeding from the assumption that experimental manipulation in a WMC task leads to increasing demands on WMC, the processes systematically varying across task conditions can be assumed to be WMC-specific. Processes not varying across task conditions, on the other hand, are probably independent of WMC. Fixed-links models allow for representing these two kinds of processes by two independent latent variables. In contrast to traditional CFA where a common latent variable is derived from the different task conditions, fixed-links models facilitate a more precise or purified representation of the WMC-related processes of interest. By using fixed-links modeling to analyze data of 200 participants, we identified a non-experimental latent variable, representing processes that remained constant irrespective of the WMC task conditions, and an experimental latent variable which reflected processes that varied as a function of experimental manipulation. This latter variable represents the increasing demands on WMC and, hence, was considered a purified measure of WMC controlled for the constant processes. Fixed-links modeling showed that both the purified measure of WMC (β = .48) as well as the constant processes involved in the task (β = .45) were related to Gf. Taken together, these two latent variables explained the same portion of variance of Gf as a single latent variable obtained by traditional CFA (β = .65) indicating that traditional CFA causes an overestimation of the effective relationship between WMC and Gf. Thus, fixed-links modeling provides a feasible method for a more valid investigation of the functional relationship between specific constructs.
Highlights
Since Galton’s (1869) first attempt to show that individuals differ in their mental capacities, the area of intelligence has been one of the most fascinating ones in psychology
By using fixed-links modeling to analyze data of 200 participants, we identified a non-experimental latent variable, representing processes that remained constant irrespective of the working memory capacity (WMC) task conditions, and an experimental latent variable which reflected processes that varied as a function of experimental manipulation
By applying the fixed-links modeling approach, we probed whether we could identify more than only one process underlying performance on the WMC task. For both measurement models we investigated the relationship between the derived latent variables and a measure of Gf derived from subtests of the Berlin Intelligence Structure (BIS) test (Jäger, Süss, & Beauducel, 1997)
Summary
Since Galton’s (1869) first attempt to show that individuals differ in their mental capacities, the area of intelligence has been one of the most fascinating ones in psychology. The close relationship between WMC and Gf led some researchers to assume that WMC and Gf are identical constructs (e.g., Colom, Flores-Mendoza, & Rebollo, 2003; Engle, 2002; Kyllonen, 2002; Stauffer, Ree, & Caretta, 1996). Oberauer, Schulze, Wilhelm and Süss (2005) argued that this is an underestimation because of several methodological shortcomings and biases. These latter authors reanalyzed the data examined by Ackerman et al (2005) and obtained a correlational relationship of r = .85 between the two constructs. Despite the close association between WMC and Gf, the two constructs were still clearly dissociable from each other (Oberauer et al, 2005)
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