The ERN was elicited using a variant of the Eriksen flanker task (Eriksen and Eriksen, 1974). A central arrowhead pointing to the left or right was flanked on both sides by arrowheads that pointed in the same direction (congruent trials) or the opposite direction (incongruent trials). Participants indicated the direction of the central arrowhead on each trial with a left- or right-hand buttonpress.  ---- The data are provided in two formats: I. A folder (**All Data and Scripts**) containing all of the raw and processed data files (including the results of intermediate processing steps), and the analysis scripts. II. A folder **(Raw Data and Scripts Only)** containing just the initial raw EEG data files and analysis scripts. The **Raw Data and Scripts Only** folder is much smaller, and the scripts can be used to create the intermediate processing data files. However, the **All Data and Scripts** option is useful if you have trouble getting the scripts to run or don’t want to re-run all of the processing steps. Within each folder, you will find: 1. Data files from 40 participants, located in subject folders 1-40 2. Archival copies of the EEGLAB/ERPLAB scripts and accessory files used for analyzing the data, located in "EEG_ERP_Processing," "Behavior_Measurements," and "Noise_Measurements" folders. The current versions of the scripts are hosted on GitHub (https://github.com/lucklab/ERP_CORE), and it is strongly recommended that these updated scripts are used instead of the archival copies found here. 3. The event code scheme for the task ("ERN_Event_Code_Scheme.xlsx") 4. A spreadsheet containing demographic information for all 40 participants ("Participant_Demographics.xlsx") 5. A spreadsheet containing a list of participants included/excluded in the final analysis with reasons for exclusions ("ERN_Subject_Summary.xlsx") 6. The versions of EEGLAB (v.13.4.4b) and ERPLAB (v.8.0.0) that were used in conducting the original analyses ("eeglab_13_4_4b.zip") III. A folder (**Raw Data BIDS-Compatible**) containing BIDS-formatted versions of the raw EEG files along with all the associated files required by the BIDS specification. --- For more details, please see the README file located in each folder.