Neuronal Distortions of Reward Probability without Choice

Abstract

Reward probability crucially determines the value of outcomes. A basic phenomenon, defying explanation by traditional decision theories, is that people often overweigh small and underweigh large probabilities in choices under uncertainty. However, the neuronal basis of such reward probability distortions and their position in the decision process are largely unknown. We assessed individual probability distortions with behavioral pleasantness ratings and brain imaging in the absence of choice. Dorsolateral frontal cortex regions showed experience dependent overweighting of small, and underweighting of large, probabilities whereas ventral frontal regions showed the opposite pattern. These results demonstrate distorted neuronal coding of reward probabilities in the absence of choice, stress the importance of experience with probabilistic outcomes and contrast with linear probability coding in the striatum. Input of the distorted probability estimations to decision-making mechanisms are likely to contribute to well known inconsistencies in preferences formalized in theories of behavioral economics.

Discrete coding of stimulus value, reward expectation, and reward prediction error in the dorsal striatum

“…This suggests that the striatum is preferentially involved in coding parametric reward value rather than reward uncertainty. Such a conclusion is consistent with human imaging findings (Tobler et al 2008) indicating that striatal activation is dependent on reward probability but not on reward uncertainty in a very similar probabilistic Pavlovian conditioning task. Furthermore, we found that only a small number of neurons showed negative correlations between CS-related activity and reward probability even though positive correlations between CS-related activity and reward probability were substantial and numerous.…”

The Reward Circuit: Linking Primate Anatomy and Human Imaging

“…For instance, some studies find that VS activation peaks at intermediate probability levels, consistent with maximal uncertainty (Cooper and Knutson, 2008;Dreher et al, 2006;Knutson et al, 2005;Preuschoff et al, 2006). Other studies, however, have reported linear effects of anticipated reward probability on VS activation (Abler et al, 2006;Hsu et al, 2009;Tobler et al, 2008;Yacubian et al, 2006). A large subsequent study investigated the possibility that different subcomponents within the VS showed greater sensitivity to anticipated reward magnitude vs probability (Yacubian et al, 2007).…”

Mean-Variance or Prospect Theory? The Nature of Value Representations in the Human Brain

“…The loci of activations and the nature of nonlinear probability functions can be contrasted with those from two recent experiments (Berns et al, 2008;Tobler et al, 2008). Numerous factors may explain discrepancies between these studies: the way probabilities were presented to subjects (alphanumerically or learned through experience), the experience of feedback, the range of probabilities used, the context (positive or negative outcomes), and the specific analyses conducted.…”