Hierarchical Hidden Markov Models

In a recent post, famous futurist Ray Kurzweil mentions that -- in his opinion -- brain structures in the neocortex are technically similar to hierarchical hidden Markov models (HHMM). An idea he also explained in more detail in his 2012 book "How to Create a Mind" [1]. Unfortunately though, neither the article nor the book has enough information to understand this machine learning model in detail, let alone implement it. So, let's use this article to try and understand hierarchical hidden Markov models. We'll have a brief, high-level look at most of the concepts it builds on and prepare the stage for an actual implementation (which will follow in another article due to content length).