Intelligence test items varying in capacity demands cannot be used to test the causality of working memory capacity for fluid intelligence

Klaus Oberauer,Gidon T Frischkorn

doi:10.3758/s13423-021-01909-w

Abstract

There is a strong relationship between fluid intelligence and working memory capacity (WMC). Yet, the cognitive mechanisms underlying this relationship remain elusive. The capacity hypothesis states that this relationship is due to limitations in the amount of information that can be stored and held active in working memory. Previous research aimed at testing the capacity hypothesis assumed that it implies stronger relationships of intelligence test performance with WMC for test items with higher capacity demands. The present article addresses this assumption through simulations of three theoretical models implementing the capacity hypothesis while systematically varying different psychometric variables. The results show that almost any relation between the capacity demands of items and their correlation with WMC can be obtained. Therefore, the assumption made by previous studies does not hold: The capacity hypothesis does not imply stronger correlations of WMC and intelligence test items with higher capacity demands. Items varying in capacity demands cannot be used to test the causality of WMC (or any other latent variable) for fluid intelligence.

Highlights

Individual differences in fluid intelligence – the ability to “reason and solve problems involving new information” (Carpenter et al, 1990 p.404) – are strongly correlated with measures of working memory capacity (WMC; Conway & Kovacs, 2013; Kyllonen & Christal, 1990; Oberauer et al, 2005)
They found that with increasing number of rule tokens required for solving an item its mean error rate increased
The aim of the presented simulation study was to assess what the capacity hypothesis implies for the pattern of correlation of items varying in their capacity demands with WMC

Summary

Introduction

Individual differences in fluid intelligence – the ability to “reason and solve problems involving new information” (Carpenter et al, 1990 p.404) – are strongly correlated with measures of working memory capacity (WMC; Conway & Kovacs, 2013; Kyllonen & Christal, 1990; Oberauer et al, 2005). To reflect these conceptualizations of WMC, we specified two additional models that change the generic model in some respects We assess whether these models change what is better able to differentiate between people high and low in ability around its location (i.e., item difficulty), both floor and ceiling effects – as illustrated on the left side – can occur for items with high discrimination the capacity hypothesis implies for the relationship of WMC and intelligence test items with varying capacity demands. Authors of several previous studies assumed that the capacity hypothesis, stating that WMC causally underlies individual differences in intelligence test performance, implies increasing correlations for items with higher capacity demands and measures of WMC. If this assumption is false, a multitude of different correlation patterns across items with varying capacity demands could arise that are all in line with the capacity hypothesis

Procedure of the simulation study

Evaluation of simulation results

Results

Discussion