Self Organized Maps (SOM) neighborhood and weight updates

Question

I am studying Self Organized Map (SOM) in the Neuron Nets field. So I have 2 questions:

1) Why neighborhood size is decreasing? 2) why not update just the winner? What would happen in this case?

Thanks in advance

Answer 1

The power of the SOM is to create a neural network that will be displayable and human readable, so:

1) The neighborhood size is decreased in order to get some stability in the algorithm increasing the iterations.

2) The mean of updating also the neighborhood is to create the map (that will be displayable) where near units have similar weights. If you update only the winner unit, the map will be not created since similar units will be left scattered in the map.