The group output types form a pipeline of functions which compute the units' outputs in the forward direction and backpropagate the outputDerivs in the backward direction. The basic types determine the output as a function of the input. The clamping types set or alter the output based on the externalInput. The other types modify an already-computed output value. There shouldn't be more than one basic type. There may be no basic type if there is a clamping type.
In the backward pass, the inputDeriv of units in the neighborhood will be set to 1.0 and that of the others to 0.0. Only units in the neighborhood will be able to alter their incoming weights. The DISTANCE procedure, in the backward pass, will cause the incoming weights to drift towards the input vector.