Abstract
Cognitive training and brain stimulation studies have suggested that human cognition, primarily working memory and attention control processes, can be enhanced. Some authors claim that gains (i.e., post-test minus pretest scores) from such interventions are unevenly distributed among people. The magnification account (expressed by the evangelical “who has will more be given”) predicts that the largest gains will be shown by the most cognitively efficient people, who will also be most effective in exploiting interventions. In contrast, the compensation account (“who has will less be given”) predicts that such people already perform at ceiling, so interventions will yield the largest gains in the least cognitively efficient people. Evidence for this latter account comes from reported negative correlations between the pretest and the training/stimulation gain. In this paper, with the use of mathematical derivations and simulation methods, we show that such correlations are pure statistical artifacts caused by the widely known methodological error called “regression to the mean”. Unfortunately, more advanced methods, such as alternative measures, linear models, and control groups do not guarantee correct assessment of the compensation effect either. The only correct method is to use direct modeling of correlations between latent true measures and gain. As to date no training/stimulation study has correctly used this method to provide evidence in favor of the compensation account, we must conclude that most (if not all) of the evidence should be considered inconclusive.
Highlights
In social sciences and other disciplines dealing with living organisms, researchers often study the effects of interventions
A series of simulations was performed in order to establish which of the methods described above yields an acceptable estimate of the compensation effect, or which can validly detect the lack of the effect. 10,000 simulations were run in order to achieve a level of accuracy higher than 99%, taking into account the established variance of the parameters of interest, the effect size and α value of .05. (Burton, Altman, Royston, & Holder, 2006)
The correlation with alternative measure failed to detect the existent compensation in small and medium samples; the method almost indicated the effect in the medium sample (p = .06) and correctly detected the effect in the large and huge samples
Summary
In social sciences and other disciplines dealing with living organisms (e.g., medicine, agriculture), researchers often study the effects of interventions. In cognitive and developmental psychology, recent years have brought a multitude of studies focused on the positive effects of training cognitive abilities such as working memory, attention, and reasoning. There is still heated debate on whether the far transfer of a trained ability, such as the increase in reasoning ability when working memory is trained, is possible There is little doubt that in terms of near transfer, the existing cognitive training methods are effective (Klingberg, 2010; Morrison & Chain, 2011; Shipstead, Redick, & Engle, 2012). More recent reports from neuroscience have even suggested the possibility of enhancing cognitive processing via noninvasive transcranial electrical stimulation with direct or alternating currents (e.g., Jausovec & Pahor, 2017; Pahor & Jausovec, 2014; Polanıa, Nitsche, Korman, Batsikadze, & Paulus, 2012; Santarnecchi et al, 2015, 2016)
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