[SurfingToad]

Based on the replies so far, I think most of you would find Schmidhuber's Compression Progress Drive interesting. The idea is essentially that of an adversarial agent with two components. A attempts of to compress its entire life history, breaking it all into neat chunks. B gets off on A's progress in so doing, and finds/creates patterns that are just within A's reach. So B's intrinsic motivation comes from discovering novel patterns that are broken down by A.

You can get really far with this idea, and music is the perfect example. We enjoy patterns. Complicated patterns become more interesting with listening experience. Simple patterns are quickly exhausted. So long as there is structure, there is opportunity for enjoyment.

Of course, Schmidhuber's theory is a bit more complicated than that. And his own opinion of it is a bit ... grandiose. Title of one of his papers on the topic: "Driven by Compression Progress: A Simple Principle Explains Essential Aspects of Subjective Beauty, Novelty, Surprise, Interestingness, Attention, Curiosity, Creativity, Art, Science, Music, Jokes"

Nonetheless, I think it's a neat theory.