THE ARTIFICAL NEURAL NETWORK e Within neural systems it is useful to distinguish three Hidden types of units: input units Input indicated by an index i Output which receive data from outside the neural network output units(indicated by an index o) which send data out of the neural network, and hidden units (indicated by an index h) whose input and output signals remain within the neural network Within neural systems it is useful to distinguish three types of units: input units (indicated by an index i) which receive data from outside the neural network, output units (indicated by an index o) which send data out of the neural network, and hidden units (indicated by an index h) whose input and output signals remain within the neural network