Figure 1.

Simulation of typical and atypical past tense acquisition predicting long-term compensated outcomes. (a) Empirical data (per cent accuracy) for typically developing children from Thomas et al. (2001) for a group of typically developing children on a past tense elicitation task for regular verbs, irregular verbs, novel verbs, and overgeneralization errors; and for a group of children with DLD from van der Lely and Ullman (2001), using the same elicitation task. Error bars show standard error of the mean. (b) Simulation data from Thomas (2005) for a connectionist past tense model, either in a typical condition or an atypical condition where the discrimination of the simple processing units was reduced by lowering the temperature of the sigmoid activation function (1 → 0.25). Model data are shown at a point that approximately matched the performance of the children (250 epochs of training). (c) Simulation data for the projected ‘adult’ outcome of typical and atypical trajectories (5000 epochs of training). The projected adult model reached ceiling on the training set but retained atypical generalization. Error bars show standard error over 10 replications with different initial random seeds.