![]() In asymmetric conditions, the two reward probabilities differed between cues (25/75%). ![]() In all conditions each cue was associated with a stationary probability of reward. In this task, options (abstract cues) were presented in fixed pairs (i.e. Healthy subjects performed a probabilistic instrumental learning task with monetary feedbacks, previously used in brain imaging, pharmacological and clinical studies 13-15 ( Figure 1A). Finally, our fMRI results confirmed at the functional level the assumptions of our computational model as well as the VBM results. Our imaging results indicate that the interindividual variability in the tendency in optimistic learning correlates with grey matter density in the dorsal prefrontal cortices. However the question remains, whether or not such interindividual differences are related to specific anatomical, supposedly developmental, variability as revealed by voxel-based morphometry (VBM). #Unrealistic optimism could best be described as an updateBehavioral differences in optimistic beliefs and optimistic update have been shown to be reflected by differences in brain activation in the prefrontal cortex ( Sharot et al., 2011). Our and previous studies suggest that the good news/bad news effect is highly variable across subjects. The good news/bad news effect can then be considered as a particular consequence of a more general asymmetry in reinforcement learning, accounting for the optimism bias. Furthermore, this tendency of using the asymmetric model covaried with optimistic trait as measured with standard psychometric scale (LOT-R). Over two experiments, we found subjects’ behavior was better explained by the asymmetric model, with an overall difference in learning rates consistent with preferential learning from positive, compared to negative, prediction errors. The first model (a standard RL algorithm) confounded individual learning rates for positive and negative feedbacks and the second one differentiated them, potentially accounting for learning asymmetries. To arbitrate between these two alternative possibilities, we analyzed instrumental behavior of subjects performing a simple two-armed bandit task, involving neutral stimuli and actual and immediate monetary outcomes, with two learning models. If the asymmetry is not found at the basic reinforcement learning level, this would mean that the asymmetry is specific of abstract belief updating, and this would require a theory explaining this discrepancy. If an asymmetric update is also found in a task involving neutral items and direct feedbacks, then the good news/bad news effect could be considered as a specific – cognitive – manifestation of a general reinforcement learning asymmetry. ![]() with no a priori desirability or undesirability). However, it remains unclear whether this learning asymmetry also applies to immediate reinforcement events driving instrumental learning directed to affectively neutral options (i.e. In this experimental context, belief formation triggers complex interactions between episodic, affective and executive cognitive functions ( Eil and Rao, 2011 Sharot et al., 2011, 2007), and belief updating relies on a learning process involving abstract probabilistic information ( Garrett et al., 2014 Moutsiana et al., 2015, 2013 Sharot et al., 2011). This good news/bad news effect has recently been demonstrated in the case where outcomes are hypothetical future prospects associated with a strong a priori desirability or undesirability (estimation of post-graduation salary or the probability of getting cancer) ( Shepperd et al., 1996 Waters et al., 2011). Indeed, preferentially revising one’s beliefs when provided with favorable compared to unfavorable information constitutes a learning bias which could, in principle, generates and sustains an overestimation of the likelihood of desired events and a concomitant underestimation of the likelihood of undesired events (optimism bias) ( Sharot and Garrett, 2016). One mechanism hypothesized to underlie this phenomenon is an asymmetry in belief updating, colloquially referred to as “the good news / bad news effect” ( Eil and Rao, 2011 Sharot et al., 2011). This cognitive trait in (healthy) humans is known as the optimism bias and has been repeatedly evidenced in many different guises and populations ( Shepperd et al., 2013, 2015 Weinstein, 1980) such as students projecting their salary after graduation ( Shepperd et al., 1996), women estimating their risk of getting breast cancer ( Waters et al., 2011) or heavy smokers assessing their risk of premature mortality ( Schoenbaum, 1997). People typically underestimate the likelihood of negative events and overestimate the likelihood of positive events. “ It is the peculiar and perpetual error of the human understanding to be more moved and excited by affirmatives than negatives whereas it ought properly to hold itself indifferently disposed towards both alike” (p. ![]()
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