**A**: Fraction of choices predicted by the model as a function of the number of choices remaining. For bars ‘3 choices to go’, for instance, it shows the fraction of times the model assigned higher

value to the subject's choice in

*all* situations where three choices remained (i.e. bar 3 in these plots encompasses all three panels in ). These are predictions only in the sense that the model predicts choice

based on history up to

. The gray line shows this statistic for the full look-ahead model, and the blue bars for the most parsimonious model (‘Pruning and Learned’).

**B**: Mean predictive probabilities, i.e. likelihood afforded to choices on trial

given learned values up to trial

.

**C**: Model comparison based on integrated Bayesian Information Criterion (

) scores. The lower the

score, the more parsimonious the model fit. For guidance, some likelihood ratios are displayed explicitly, both at the group level (fixed effect) and at the individual level (random effect). Our main guide is the group-level (fixed effect). The red star indicates the most parsimonious model.

**D,E**: Transition probability from state 6 to state 1 (which incurs a −20 loss) when a subsequent move to state 2 is possible (D; at least two moves remain) or not (E; when it is the only remaining move). Note that subjects' disadvantageous approach behavior in E (dark gray bar) is only well accommodated by a model that incorporates the extra Learned Pavlovian parameter.

**F**: Decision tree of depth 4 from starting state 3. See for colour code. Subjects prefer (width of line) the optimal (yellow) path with an early transition through a large loss (red) to an equally optimal path with a late transition through a large loss.

**G**: Phase plane analysis of specific and general pruning. Parameter values for which the left optimal yellow path in panel F is assigned a greater expected value than the right optimal path are below the blue line. Combinations that are also consistent with the notion of pruning

are shown in green. The red dot shows parameters inferred for present data (c.f. ). Throughout, errorbars indicate one standard error of the mean (red) and the 95% confidence intervals (green).

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