If a second
hidden unit is required, it is installed downstream of the first hidden unit.
hidden unit is recruited, training of the output weights resumes. Thus, these
phases are known as output phases. Learning continues in this fashion
until network error is reduced to the extent that all output units have
activations within a certain range of their targets on all training patterns.
That range is called score-threshold, a parameter that can be
manipulated to control depth of learning.