Behavioural and neural characterization of optimistic reinforcement learning


When forming and updating beliefs about future life outcomes, people tend to consider good news and to disregard bad news. This tendency is assumed to support the optimism bias. Whether this learning bias is specific to ‘high-level’ abstract belief update or a particular expression of a more general ‘low-level’ reinforcement learning process is unknown. Here we report evidence in favour of the second hypothesis. In a simple instrumental learning task, participants incorporated better-than-expected outcomes at a higher rate than worse-than-expected ones. In addition, functional imaging indicated that inter-individual difference in the expression of optimistic update corresponds to enhanced prediction error signalling in the reward circuitry. Our results constitute a step towards the understanding of the genesis of optimism bias at the neurocomputational level.

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Figure 1: Behavioural task and variables.
Figure 2: Behavioural and computational identification of optimistic reinforcement learning.
Figure 3: Functional signatures of the optimistic reinforcement learning.
Figure 4: Robustness of optimistic reinforcement learning.


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We thank Y. Worbe and M. Pessiglione for granting access to the first dataset, V. Wyart, B. Bahrami and B. Kuzmanovic for comments, and T. Sharot and N. Garrett for providing activation masks. S.P. was supported by a Marie Sklodowska-Curie Individual European Fellowship (PIEF-GA-2012 Grant 328822) and is currently supported by an ATIP-Avenir grant (R16069JS). G.L. was supported by a PhD fellowship of the Ministère de l'enseignement supérieur et de la recherche. M.L. was supported by an EU Marie Sklodowska-Curie Individual Fellowship (IF-2015 Grant 657904) and acknowledges the support of the Bettencourt-Schueller Foundation. The second experiment was supported by the ANR-ORA, NESSHI 2010–2015 research grant to S.B.-G. The Institut d’Étude de la Cognition is supported by the LabEx IEC (ANR-10-LABX-0087 IEC) and the IDEX PSL* (ANR-10-IDEX-0001-02 PSL*). The funders had no role in study design, data collection and analysis, decision to publish or preparation of the manuscript.

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G.L. performed the experiment, analysed the data and wrote the manuscript. M.L. provided analytical tools, interpreted the results and edited the manuscript. F.M. provided analytical tools and edited the manuscript. S.B.-G. interpreted the results and edited the manuscript. S.P. designed the study, performed the experiments, analysed the data and wrote the manuscript.

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Correspondence to Stefano Palminteri.

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The authors declare no competing interests.

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Supplementary Notes, Supplementary Figures 1–7, Supplementary Discussion, Supplementary Methods, Supplementary References. (PDF 606 kb)

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Lefebvre, G., Lebreton, M., Meyniel, F. et al. Behavioural and neural characterization of optimistic reinforcement learning. Nat Hum Behav 1, 0067 (2017).

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