Unsupervised manifold learning of collective behavior

PLoS Comput Biol. 2021 Feb 12;17(2):e1007811. doi: 10.1371/journal.pcbi.1007811. eCollection 2021 Feb.

Abstract

Collective behavior is an emergent property of numerous complex systems, from financial markets to cancer cells to predator-prey ecological systems. Characterizing modes of collective behavior is often done through human observation, training generative models, or other supervised learning techniques. Each of these cases requires knowledge of and a method for characterizing the macro-state(s) of the system. This presents a challenge for studying novel systems where there may be little prior knowledge. Here, we present a new unsupervised method of detecting emergent behavior in complex systems, and discerning between distinct collective behaviors. We require only metrics, d(1), d(2), defined on the set of agents, X, which measure agents' nearness in variables of interest. We apply the method of diffusion maps to the systems (X, d(i)) to recover efficient embeddings of their interaction networks. Comparing these geometries, we formulate a measure of similarity between two networks, called the map alignment statistic (MAS). A large MAS is evidence that the two networks are codetermined in some fashion, indicating an emergent relationship between the metrics d(1) and d(2). Additionally, the form of the macro-scale organization is encoded in the covariances among the two sets of diffusion map components. Using these covariances we discern between different modes of collective behavior in a data-driven, unsupervised manner. This method is demonstrated on a synthetic flocking model as well as empirical fish schooling data. We show that our state classification subdivides the known behaviors of the school in a meaningful manner, leading to a finer description of the system's behavior.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Behavior*
  • Behavior, Animal*
  • Computational Biology
  • Ecosystem
  • Fishes / physiology
  • Humans
  • Models, Biological
  • Models, Psychological
  • Social Behavior
  • Synthetic Biology
  • Systems Analysis*
  • Systems Biology
  • Unsupervised Machine Learning*

Grants and funding

This project was funded by the DARPA Young Faculty Award number N66001-17-1-4038 (MT, GH, JW). Additional support was provided by the National Oceanic and Atmospheric Administration award NOAA-AWD100582 (GH), the Simons Foundation Grant 395890 (GH), and the National Science Foundation Grant OCE-184857 (GH). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.