Careful with the temptation to simply stack SP and TM regions on top of one another. Of course it seems like the most intuitive thing to try, but it would not be a decision that has any rigorous mathematical or even biological motivation (not that much of anything in HTM has rigorous mathematical motivations). It is well known that the communication between neocortical columns who together process information in a hierarchical fashion is vastly more complex than what DL models have proposed in order to utilize backprop. I’ve always been more of a utilitarian, myself, so if something works, I don’t really care if it’s biologically motivated or not. However, my understanding of the purpose and value of HTM research itself is to always look to Biology in the effort to push AI materially ahead (which is arguably much more difficult than designing mathematical tricks on existing DL methodology). So I don’t think deviating from Biology now necessarily falls in line with everything that has led up to the current state of HTM. In other words, bandaging up an incomplete/experimental biologically-inspired model with algorithmic tricks to compete with CNNs might seem fruitless or even unnecessary. This is true when the engineer could just choose to use CNNs in the first place which have been specially designed from the very beginning for solving exactly the problem of interest (visual classification) and have tons of research/support from all over the world; whereas HTM arguably seeks to explore and answer different questions (at least that is my interpretation).
Jeff explains here more reasons why hierarchies are of less interest to Numenta:
Moreover, I’m nearly positive somebody has already experimented with stacking SP and TM regions on top of each other. I know I’ve heard it brought up many times in the past. Perhaps somebody can help me find where this has been done before.