Variability in color-choice Stroop performance within and across EEG and MRI laboratory contexts

To examine the reproducibility of the Stroop effect, behavioral data from 22 healthy female individuals were repeatedly (three-month interval between two separate measurement sessions) obtained while performing a color-choice Stroop task under realistic magnetic resonance imaging (MRI) and electroencephalography (EEG) laboratory conditions. At the group statistical level, the Stroop effect, indicated by longer response times for incongruent than for congruent stimulus conditions, was consistently present for almost all examined measurement levels. However, differential effects of laboratory contexts on retest reproducibility were observed across repeated measurement levels, both within and between sessions. These results challenge existing theories about the underlying nature of Stroop interference processing. It appears necessary to apply a multitheoretical approach, because intraindividual variability within and across measurement sessions suggests potential fluctuations in the individual mental strategies applied, recruitment of varying memory resources, the influence of mediator variables such as working memory capacity and/or attention, and many more possible variations. Single-observation studies run the risk of favoring a single theoretical concept and therefore underestimating the individual factor. We further conclude that dependent analysis-of-variance statistics are a more fit test for reproducibility than are correlative reliability estimations.