Thanks Matt. The following might help.
Numenta did not implement a Temporal Pooling (TP) layer for sequence memory ™. We talked about it a lot, but didn’t do it. However, for the past year we have been working on sensory-motor inference (SMI), and as part of that effort we have implemented a TP layer. The temporal pooling layer for sequence memory and for sensory-motor inference ideally should be identical, the TP we did for SMI should work for TM.
The TP layer forms an SDR that is unique for the object being sensed. The TP SDR is also stable over changing input as long as the underlying object being sensed is the same. To achieve the cells in the TP layer have to learn to recognize every pattern in the SMI/TM layer. Bear in mind that the SDRs in the TM/SMI layer are unique to the object. If the TM is following a melody, that is it is correctly predicting the next input, then each TM SDR can uniquely identify the melody. The TP layer will be unique, not a union, to the melody. If an input is ambiguous, or unexpected, then it will cause a union of SDRs in the TM layer wihich will cause a union of SDRs in the TP layer.
The implementation of TP we did for SRI has two more features. First, the cells in an SDR for an object form connections to each other. This means that once the TP layer has locked onto an object SDR, it will continue be biased toward that interpretation. The other difference is we model multiple columns, and the TP layers in adjacent columns reinforce each other. This way if column 1 can’t tell if the object is A or B and column 2 can’t tell if it is B or C. Together they settle on B.
Our manuscrpt describing SMI, including the TP algorithm, is very very close to finished. We hope to post it to bioArchiv within a week. In the manuscript, we show that the TP layer in a single column can reliably recognize hundreds of objects.
Using the TP layer with TM introduces one little twist. The TM sequence memory can learn extremely long sequences. That’s not true for SMI wtih objects. Ther are only so many locations on a object that can be sensed. It is likely in the brain that when you learn melodies for example, that not all notes in the melody are equally learned by the TP layer. The beginning of the melody and the refrains would be more likely. I would expect that it is easier to name the tune at the beginning and during refrains (they repeat more)…
Jeff