The aims of unsupervised learning
	• We would like to extract a representation of the sensory input that is useful for later processing. – We want to do this without requiring labeled data. • Prior ideas about what the internal representation should look like ought to be helpful. So what would we like in a representation? – Hidden causes that explain high-order correlations? – Constraints that often hold? – A low-dimensional manifold that contains all the data? – Properties that are invariant across space or time?