Variability in Preprocessing and Analysis of the Error-Related Negativity in Adult Response-Conflict Studies: A Systematic Review.

The analysis of EEG (electroencephalography) data affords many defensible choices, creating substantial researcher degrees of freedom. While stimulus-locked components such as the N400 show wide methodological variability and incomplete reporting, it has been unclear whether this generalizes to the response-locked error-related negativity (ERN). We conducted a PRISMA-guided systematic review of ERN studies published 1995-2025. From a chronologically stratified sample of 202 studies of adults using conventional response-conflict tasks and conventional ERP analyses, we extracted preprocessing and quantification choices, assessed reporting completeness, examined temporal trends, and tested predictors of pipeline decisions (e.g., montage size, amplifier, analysis software, task). ERN pipelines and order of analysis steps were highly heterogeneous, no two studies used the same workflow, and reporting gaps persisted. Several analytic decisions showed modest temporal shifts, yet overall diversity remained high. Sample sizes increased over time but remained insufficient for typical small-to-moderate sized effects, and detailed preregistrations were extremely rare. None of the 32 processing and analysis choices examined in more detail varied systematically by task, and only a subset was linked to recording parameters (e.g., montage size, amplifier, analysis software). Across adult ERN studies using conventional response-conflict tasks and conventional ERP analyses, we observed substantial methodological heterogeneity, limited convergence in analytic practice, and considerable potential for analytic flexibility. Together this may complicate the comparison and synthesis of findings across studies.