Figure 7: Savings.
(a–d) To examine our model’s ability to explain the short-term savings effect, we considered an experiment in which a 30° visual rotation was applied for 30 trials (the initial learning phase), followed by a −30° visuomotor rotation for 5 trials (the opposite learning phase), and another set of the 30° visual rotation for 30 trials (the relearning phase). (a) Trial-by-trial change of pt and xt averaged across 10 simulations of short-term savings. (b) The activity of each primitive, with a strong white colour indicating high activity. The red line denotes the prospective error, êt. Vertical dotted lines are drawn at the trials when the phases switched. The horizontal dotted line denotes the line on which êt=0. (c) Weighting parameters of each primitive. Blue and red colours indicate weighting parameters to compensate for perturbations of positive and negative values, respectively. (d) Comparison of xt between the initial learning and relearning phases. (e) Persistence of the savings effect and its dependence on the forgetting rate (λ=0.9586 (best-fit parameter for the data of group 1), 9786 or 9986). We simulated an experiment in which a 30° visual rotation was applied for 60 trials (the initial learning phase) followed by a 0° visuomotor rotation (washout phase), and another set of the 30° visual rotation was imposed for 20 trials (the relearning phase). The horizontal axis denotes the length of the washout trials. (Inset) comparison of xt between the initial learning and relearning phases. We define the savings effect as the integral of the grey zone: the difference of xt in the first five trials between the initial learning and relearning phases. This value should be 0 if there are no savings, and the value is positive when the learning speed in the relearning phase is higher than that in the initial learning phase. The savings effects were normalized by setting the maximal value to be 1. (f) Previously reported savings by Krakauer et al.18 (adapted by permission from Macmillan Publishers Ltd: Nature Neuroscience18, copyright 1999).
