Article Figures & Data
Figures
- Figure 1.
Experimental setup and behavior. a, Two response options (white boxes on the left/right of fixation) were shown on the screen until a response was given. A correct response was rewarded with a 70% probability (50 cent coin) and not rewarded with a 30% probability (1 cent coin). Reward visibility was manipulated by masking. Unmasked (long coin presentation, short backward mask presentation) and masked (short coin presentation, long backward mask presentation) reward trials were mixed within blocks and randomly chosen across trials (each with a 50% probability). Which response option was most rewarded changed every 75–125 trials. b, The percentage of switches, at the group level (in black) and for individual subjects (in gray) after specific trials. M: masked; UM: unmasked; +: reward; −: no-reward; error bars represent ± s.e.m.
- Figure 2.
Modeling approach. a, The computational architecture used to build the model space. b, Model space. Eighteen models were built by systematically combining the different options available for the different computational modules. c, Model identifiability analysis. Data from 32 synthetic participants were simulated with each of our 18 models. Bayesian model selection was used to identify the most probable model generating the data, using model exceedance probability. This procedure was repeated 50 times. Overall, all 18 models were correctly identified more than 90% of the time (>45 out of 50 simulations, see top confusion matrix), with an average exceedance probability > 90% (bottom confusion matrix). d, Parameter recovery analysis - general. Overall, data from 1600 synthetic participants (50 simulations × 32 individuals) were simulated with the full model (model 18). The 6 estimated parameters per participants were then regressed against the true parameters used for simulating the data. Results show very good identifiability, with regression intercepts (β0s) close to 0, regression slopes (β1s) close to 1 and highly significant (all p-values lower than Matlab's precision –i.e. reported as = 0). Each dot represents a synthetic individual. The black dotted lines represent the identity line, the red continuous lines the best linear fits, and the shaded grey areas the 95% confidence interval around the best-linear fit. The grey densities represent the probability distributions used to sample the parameters. e, Parameter recovery analysis – individual simulations. The confusion matrices represent summary statistics of the correlations between parameters, estimated over 32-subjects simulations, and averaged over the 50 simulations. Diagonal: correlations between simulated and estimated parameters. Off diagonal: cross correlation between estimated parameters. Top: Pearson correlation (R). Bottom: explained variance (R2).
- Figure 3.
a, Time course of the learning task by three representative participants (participant numbers 10, 20 and 30). The x-axis represents blocks of trials during the experiment and the y-axis represents the local fraction of left-hand responses selected by the participant. Thick black and gray lines represent the reward probability in the different blocks (75–125 trials). Gray-dotted lines represent the local fraction of left-hand responses. Green thick line represent the local probability of left-hand responses predicted by the computational model. Both behavioral choices and model predictions are averaged over 12 trials bins, and aligned on block transitions. b, Model parameters for masked and unmasked conditions. Left: value weight. Middle: learning rate. Right: perseveration weight. M: masked reward, UM: unmasked reward. Histograms and error bars represent mean ± s.e.m. Connected dots represent individual parameters. c, Model comparison. Results of a Bayesian model comparison analysis on our participants′ data. White histograms indicate the exceedance probability of each model, and grey dots their expected frequencies. d, Relative BIC. Bayesian Information Criterion (BIC) of each model, compared to the best fitting model BIC (model 18). BICs are computed at the individual level (random effects). Histogram and error bars represent mean ± s.e.m.
- Figure 4.
ERP results. ERPs for no-reward (red lines) and reward (green lines) for unmasked a, and masked conditions. b, Time = 0 ms is reward presentation. The lower dotted black lines indicate significant time-windows, FDR corrected across the entire ERP time-window (p < 0.05). Topographical distribution maps of the reward valence effect (no-reward minus reward, − vs +) were taken from the three broad time-windows (100–300 ms, 300–500 ms and 500–800 ms; scaling maps unmasked reward from left to right: [−2:2], [−5:5], [−2:2]; scaling maps masked reward: [−2:2]). Error bars represent ± s.e.m.
- Figure 5.
Model-based EEG analysis. a, The time courses of regression weights of the signed PE regressed on the reward-locked EEG signal derived from a central ROI. Effects are plotted separately for unmasked (green) and masked (black) reward outcomes. Shaded areas indicate the s.e.m. Topographical maps show the regression weights during the relevant time windows. Both unmasked and masked reward showed early and mid-latency EEG-PE covariations which are shown in b. Note that the polarities of these components are reversed compared to the ERP results, which in accordance with our expectations, because these ERP modulations are all associated with negative PE values, leading to a reversal of the polarities (maps: 100–300 ms and 300–500 ms; scaling: early masked = [−0.5:0.5], mid-latency masked = [−0.5:0.5], early unmasked = [−1:1], middle unmasked = [−3:3]). Bar plots of the signed PE effect for the three time-windows of interest. b, The time courses of regression weights of the unsigned PE, or the level of surprise, regressed on reward-locked EEG signal derived from a central ROI. Both unmasked and masked rewards showed late EEG-surprise covariations (maps: 300–800 ms; scaling: masked = [−0.5:0.5], unmasked = [−2:2]). Bar plots of the surprise effect. c, The time courses of regression weights of switch/stay behavior regressed on the reward-locked EEG signal derived from a central ROI. Both unmasked and masked reward showed late EEG-switch/stay behavior covariations (maps: 300–800 ms; scaling: masked = [−3:3], unmasked = [−3:3]). Bar plots of the switch/stay behavior effect. Error bars represent ± s.e.m. M: masked reward, UM: unmasked reward.
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