Hierarchical Event Descriptor (HED) tags for analysis of event-related EEG studies

Data from well-designed EEG experiments should find uses beyond initial reports, even when study authors cannot anticipate how it may contribute to future analyses. Several ontologies have been proposed for describing events in cognitive experiments to make data available for re-use and meta-analysis, but none are widely used. One reason for this is that the tools needed to make use of these ontologies are complex, placing a significant burden on experimenters while not providing any immediate reward for their efforts. Here we propose an extensible, user-friendly experiment event tagging method built on the BrainMap and CogPO ontologies and similar to the object tagging style used extensively on the Web. Hierarchical Event Descriptor (HED) tags, a hierarchy of standard and extended descriptors for EEG experimental events, provide a uniform human- and machine-readable interface facilitating use of an underlying event-description ontology during EEG data acquisition, analysis, and sharing. HED tags may be used to mark and annotate all known events in an experimental session. We describe an available real-time EEG experiment control and recording system that uses HED tags for annotation, transmission and storage of detailed information about events in EEG experiments.