Abstract
Real-world brain imaging by EEG requires accurate annotation of complex subject-environment interactions in event-rich tasks and paradigms. This paper describes the evolution of the Hierarchical Event Descriptor (HED) system for systematically describing both laboratory and real-world events. HED version 2, first described here, provides the semantic capability of describing a variety of subject and environmental states. HED descriptions can include stimulus presentation events on screen or in virtual worlds, experimental or spontaneous events occurring in the real world environment, and events experienced via one or multiple sensory modalities. Furthermore, HED 2 can distinguish between the mere presence of an object and its actual (or putative) perception by a subject. Although the HED framework has implicit ontological and linked data representations, the user-interface for HED annotation is more intuitive than traditional ontological annotation. We believe that hiding the formal representations allows for a more user-friendly interface, making consistent, detailed tagging of experimental, and real-world events possible for research users. HED is extensible while retaining the advantages of having an enforced common core vocabulary. We have developed a collection of tools to support HED tag assignment and validation; these are available at hedtags.org. A plug-in for EEGLAB (sccn.ucsd.edu/eeglab), CTAGGER, is also available to speed the process of tagging existing studies.
Highlights
In traditional EEG experiments, participants in controlled environments react to tachistoscopic presentation of stimuli in at most a few categories
For event instance E identified with the URI hedtags.org/schema/v2/EventInstance/123 and associated with Hierarchical Event Descriptor (HED) string HS identified with URI H = hedtags.org/schema/v2/HEDString/HS’ where HS’ is a normalized version of HS we have: E rdfs:type H
Open fMRI documents events, which in this context are mainly participant responses, as behavioral data stored in tab-separated text files
Summary
In traditional EEG experiments, participants in controlled environments react to tachistoscopic presentation of stimuli in at most a few categories. HED tags may appear in the overall description of an experiment or as annotations associated with individual events.
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