Brief history of HED#
Hierarchical Event Descriptors (HED) has evolved through three major generations since its inception in 2010, each representing significant advances in annotation capability and user experience.
HED generation 1 (2010-2016)#
Versions: < 4.0.0
The first version of HED was proposed and developed by Nima Bigdely-Shamlo in 2010 as part of his PhD thesis under the supervision of Scott Makeig and Kenneth Kreutz-delgado at the Swartz Center for Computational Neuroscience (SCCN), UCSD. The system was created to support event annotation in HeadIT, an early public repository for EEG data (Bigdely-Shamlo et al. 2013).
HED Generation 1 was organized around a single event hierarchy with root Time-Locked Event and immediate children Stimulus and Response. This initial design provided a foundation for structured event annotation but was limited in scope and flexibility.
HED generation 2 (2016-2021)#
Versions: 4.0.0 to 7.x.x
In 2010, the Army Research Laboratory began funding a multi-institution neuroergonomics project focused on instrumenting the brain and body at work (ARL W911NF-10-2-0022). This project included development of the https://cancta.net repository for data collected using the standardized EEG Study Schema (ESS) format to enable data sharing and cross-study analysis.
Recognizing the need for greater vocabulary flexibility, a working group led by Kay Robbins of the University of Texas San Antonio redesigned HED to accommodate annotation of more diverse datasets. The key innovation was reorganizing HED as an orthogonal sub-tag system rather than a single hierarchy. HED Generation 2 was first released in 2016 and iteratively improved over several years, with validators and online tools developed to support adoption.
A major milestone occurred in 2019 when the BIDS (Brain Imaging Data Structure) standards group incorporated HED as an annotation mechanism, significantly expanding its reach in the neuroimaging community.
HED generation 3 (2021-present)#
Versions: 8.0.0+
Work began in 2019 on a fundamental rethinking of HED vocabulary design, culminating in the release of HED Generation 3 in August 2021. This generation represents a dramatic increase in annotation capacity and significant simplification of the user experience.
Key innovations in HED Generation 3
Improved vocabulary structure - More intuitive organization and expanded coverage
Short-form annotation - Simplified syntax for common use cases
Library schema - Domain-specific extensions to the core vocabulary
Definitions - Reusable annotation patterns with placeholders
Temporal scope - Enhanced representation of time-based relationships
Encoding of experimental design - Better support for complex experimental structures
HED Generation 3 is currently maintained and developed by the HED Working Group led by Kay Robbins, Scott Makeig, and Yahya Shirazi with key contributors including Dung Truong, Monique Denissen, Dora Hermes Miller, and Arnaud Delorme.
Funding and support#
HED development has been supported by multiple funding sources across its evolution:
Generation 1: The Swartz Foundation and NIH grants R01-MH084819 (Makeig, Grethe PIs) and R01-NS047293 (Makeig PI)
Generation 2: The Cognition and Neuroergonomics Collaborative Technology Alliance (CaN CTA) program of U.S Army Research Laboratory (ARL) under Cooperative Agreement W911NF-10-2-0022
Generation 3: NIH grant RF1-MH126700.
Community and participation#
HED is an open research community effort. Researchers and developers interested in contributing are invited to participate. Visit the HED project homepagefor links to the latest developments.
For questions, email: hed.maintainers@gmail.com or post an issue at hed-issues.