HFM: Hierarchical Features Maps
If the data is strongly hierarchical, visualizing it on a flat SOM may make the hierarchy hard to see. With HFM, a hierarchy of maps is self-organized, with the high-level categories separated on top, and gradually more fine distinctions in the bottom. For example script-based story data can be visualized this way, and it forms a good foundation for episodic memory organization in story processing (see the NLP page).