Biological Computation

178    ◾    Biological Computation

regions from 8 of the 12 groups in the rst layer. (Every group of 4 × 4

neurons observes a dierent combination of eight groups.)

• e third hidden layer contains 30 neurons, all of which are con-

nected to all the neurons in the previous layer.

• e output layer contains 10 neurons representing each of the digits,

all of which are connected to all the neurons in the previous layer.

e identity of the input digit is determined by the identity of the

most active output neuron.

e network contained 1256 neurons, 64,600 edges and 9760 weights

that had to be learned. e network was trained on 7300 digits and tested

on 2000 images. e error rate was 1% on the training set and 5% on the

test set. e latter could ...