A multiple cause mixture model for unsupervised learning

  • Authors:
  • Eric Saund

  • Affiliations:
  • -

  • Venue:
  • Neural Computation
  • Year:
  • 1995

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Abstract

This paper presents a formulation for unsupervised learning ofclusters reflecting multiple causal structure in binary data.Unlike the "hard" k-means clustering algorithm and the"soft" mixture model, each of which assumes that a single hiddenevent generates each data point, a multiple cause model accountsfor observed data by combining assertions from many hidden causes,each of which can pertain to varying degree to any subset of theobservable dimensions. We employ an objective function anditerative gradient descent learning algorithm resembling theconventional mixture model. A crucial issue is the mixingfunction for combining beliefs from different cluster centersin order to generate data predictions whose errors are minimizedboth during recognition and learning. The mixing functionconstitutes a prior assumption about underlying structuralregularities of the data domain; we demonstrate a weakness inherentto the popular weighted sum followed by sigmoid squashing, andoffer alternative forms of the nonlinearity for two types of datadomain. Results are presented demonstrating the algorithm's abilitysuccessfully to discover coherent multiple causal representationsin several experimental data sets.