Working memory capacity and fluid abilities: The more difficult the item, the more more is better


Recent evidence has suggested that the relationship between a test of fluid intelligence, Raven's Progressive Matrices, and working memory capacity (WMC) may be invariant across difficulty levels of the Raven's items. We show that this invariance can only be observed if the overall correlation between Raven's and WMC is low. We demonstrate that by using a composite measure of WMC, which yields a higher correlation between WMC and Raven's than reported in previous studies, that there was a significant positive relationship between Raven's item difficulty and the extent of the itemwise correlation with WMC. This result puts strong constraints on theories of reasoning and challenges some existing views.

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