Redundancy Reduction as a Strategy for Unsupervised Learning

A redundancy reduction strategy, which can be applied in stages, is proposed as a way to learn as efficiently as possible the statistical properties of an ensemble of sensory messages. The method works best for inputs consisting of strongly correlated groups, that is features, with weaker statistical dependence between different features. This is the case for localized objects in an image or for words in a text. A local feature measure determining how much a single feature reduces the total redundancy is derived which turns out to depend only on the probability of the feature and of its components, but not on the statistical properties of any other features. The locality of this measure makes it ideal as the basis for a "neural" implementation of redundancy reduction, and an example of a very simple non-Hebbian algorithm is given. The effect of noise on learning redundancy is also discussed.