Elucidating the Functional Relationship Between Working Memory
Capacity and Psychometric Intelligence: A Fixed-Links Modeling Approach for
Experimental Repeated-Measures Designs |
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Authors: | Philipp Thomas Thomas Rammsayer Karl Schweizer Stefan Troche |
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Institution: | 1University of Bern, Department of Psychology and Center for
Cognition, Learning and Memory;2Johann Wolfgang Goethe University Frankfurt, Department of
Psychology;3University of Witten / Herdecke, Department of Psychology and
Psychotherapy |
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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. |
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Keywords: | working memory capacity fluid intelligence fixed-links modeling confirmatory factor analysis |
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