Figure 3. PCA network architecture.

Two input units (one corresponding to AD, one to SS) are fully connected to two output units via feed-forward excitatory weights (solid arrows) without any hidden layer or bias. The first output unit projects inhibitory weights (dashed lines) back to the inputs, effectively removing the principal component from the inputs and leaving the second output to encode remaining (orthogonal) covariance. Euclidean distances among output patterns were calculated after each epoch.