Spatial pooler details
We can now go through everything the spatial pooling function does.
1) Start with an input consisting of a fixed number of bits. These bits might represent sensory data or they might come from another region lower in the hierarchy.
2) Assign a fixed number of columns to the region receiving this input. Each column has an associated dendrite segment. Each dendrite segment has a set of potential synapses representing a subset of the input bits. Each potential synapse has a permanence value. Based on their permanence values, some of the potential synapses will be valid.
3) For any given input, determine how many valid synapses on each column are connected to active input bits. 4) The number of active synapses is multiplied by a “boosting” factor which is dynamically determined by how often a column is active relative to its neighbors.
5) The columns with the highest activations after boosting disable all but a fixed percentage of the columns within an inhibition radius. The inhibition radius is itself dynamically determined by the spread (or “fan-out”) of input bits. There is now a sparse set of active columns.
6) For each of the active columns, we adjust the permanence values of all the potential synapses. The permanence values of synapses aligned with active input bits are increased. The permanence values of synapses aligned with inactive input bits are decreased. The changes made to permanence values may change some synapses from being valid to not valid, and vice-versa.
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