Fig. 4.

Simulation of the Probabilistic Selection Task using our learned parameters and model (for 250 participants). (a) Simulation results of the Probabilistic Selection Task (upper row) compared to human results (lower row, reprinted from [20] with permission). Error bars illustrate standard errors of the means. Only the younger and older simulated groups are displayed for easier comparison (see Fig. S2 for full plots). Left, average difference during training on block 1 between the probability of re-selecting the response that was rewarded on the preceding trial, compared to the probability of shifting the response from the one punished on the preceding trial. Younger adults showed higher difference than older adults (Age × Preference: [F(2,247)=13.199, p<0.0001]; pairwise comparisons for younger vs. older: p<0.0001). Middle, Learning Bias changes. Average performance at test on novel pairings of stimuli that were previously mostly rewarded (‘Choose A’) compared to novel pairings of stimuli that were previously mostly punished (‘Avoid B’). Younger adults had a higher difference between the two than older adults (Age X Preference: [F(2,247)=14.257, p<0.0001]; pairwise comparisons for younger vs. older: p<0.04). Right, learning biases (defined as the difference between ‘Choose A’ and ‘Avoid B’) for all participants, ordered by bias values. Whereas younger adults had many more individuals with a positive learning bias than negative learning bias, the numbers were more evenly distributed in the older group. (b) Left, learning bias as a function of the Learning Rate Imbalance, showing a strong negative correlation (r(248)=0.61, p<0.0001). Right, learning bias as a function of the learning rate disparity, showing an inverted U-shape. Low learning bias is achieved either with very low disparity values (in line with ‘harm avoidant’ learning pattern previously hypothesized to characterize PD patients) or with very high disparity values (in line with ‘reward-seeking’ learning pattern, which most older adults in our study actually belonged to; see Fig. 3c).