Interactive effects of working memory and trial history on Stroop interference in cognitively healthy aging

Past studies have suggested that Stroop interference increases with age; however the robustness of this effect after controlling for processing speed has been questioned. Both working memory (WM) and the congruency of the immediately preceding trial have also been shown to moderate the magnitude of Stroop interference. Specifically, interference is smaller both for individuals with higher working memory capacity and following an incongruent trial. At present, it is unclear whether and how these 3 variables (age, WM and previous congruency) interact to predict interference effects in the standard Stroop color-naming task. We present analyses of Stroop interference in a large database of Stroop color-naming trials from a lifespan sample of well-screened, cognitively healthy, older adults. Our results indicated age-related increases in interference (after controlling for processing speed) that were exaggerated for individuals with low WM. This relationship between age and WM occurred primarily when the immediately preceding trial was congruent. Following an incongruent trial, interference increased consistently with age, regardless of WM. Taken together, these results support previous accounts of multiple mechanisms underlying control in the Stroop task and provide insight into how each component is jointly affected by age, WM, and trial history.