Fig. 8. Trajectories of weight changes during sequential and simultaneous training. (A) The network of two configural units (U1 and U2) and the inputs to them (L1, C1) (L2, C2). The weights (w) of the bracketed inputs to both U1 and U2 have been summed to give the axes of weight space in panels B and C. (B) The initial values of wC2 +wL2 (indicated by S) for both U1 and U2 are close. In consequence, U1 and U2 compete for the control of C2 at the start of simultaneous training. This interference keeps the input weights to U1 within the dashed circle. Eventually, the conflict is resolved and the input weights to U1 and U2 diverge. Interference is avoided with sequential training because the weights of U1 and U2 have separated to the positions S1 by the end of the first stage of training. (C) When the initial weights of U1 and U2 are well separated, there is no interference with simultaneous training, and thus no benefit from sequential training.