Synapses. Synapses on an HTM cell have a binary weight
Synapses on an HTM cell have a binary weight. There is nothing in the HTM model that precludes scalar synapse weights, but due to the use of sparse distributed patterns we have not yet had a need to use scalar weights.
However, synapses on an HTM cell have a scalar value called “permanence” which is adjusted during learning. A 0.0 permanence value represents a potential synapse which is not valid and has not progressed at all towards becoming a valid synapse. A permanence value above a threshold (typically 0.2) represents a synapse that has just connected but could easily be un-connected. A high permanence value, for example 0.9, represents a synapse that is connected and cannot easily be un- connected.
The number of valid synapses on the proximal and distal dendrite segments of an HTM cell is not fixed. It changes as the cell is exposed to patterns. For example, the number of valid synapses on the distal dendrites is dependent on the temporal structure of the data. If there are no persistent temporal patterns in the input to the region, then all the synapses on distal segments would have low permanence values and very few synapses would be valid. If there is a lot of temporal structure in the input stream, then we will find many valid synapses with high permanence.
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