Combinations of low-level and high-level neural processes can account for distinct patterns of context-dependent choice
Context effects have been explained by either high-level cognitive processes or low-level neural adjustments but not their combination. It is currently unclear how these processes interact to shape individuals responses to context. Here, we used a large cohort of human subjects in experiments involving choice between two or three gambles in order to study the dependence of context effects on neural adaptation and individuals risk attitudes. We found no evidence that neural adaptation on long timescales (~100 trials) contributes to context effects. However, we identified two groups of subjects with distinct patterns of responses to decoys, both of which depended on individuals risk aversion. Subjects in the first group exhibited strong, consistent decoy effects and became more risk averse due to decoy presentation. In contrast, subjects in the second group did not show consistent decoy effects and became more risk seeking. The degree of change in risk aversion due to decoy presentation was positively correlated with the initial degrees of risk aversion. To explain these results and reveal underlying neural mechanisms, we developed a new model that incorporates both low- and high-level processes to fit individuals choice behavior. We found that observed decoy effects can be explained by a combination of adjustments in neural representations and competitive weighting of reward attributes, both of which depend on risk aversion but in opposite directions. Altogether, our results demonstrate how a combination of low- and high-level processes shapes multi-attribute choice, modulates overall risk preference, and explains distinct behavioral phenotypes. Significance statementA large body of experimental work has illustrated that the introduction of a new, and often irrelevant, option can influence preference among the existing options, a phenomenon referred to as context or decoy effects. Although context effects have been explained by high-level cognitive processes--such as comparisons and competitions between attributes--or low-level adjustments of neural representations, it is unclear how these processes interact to shape individuals responses to context. Here, we show that both high-level cognitive processes and low-level neural adjustments shift risk preference during choice between multiple options but in opposite directions. Moreover, we demonstrate that a combination of these processes can account for distinct patterns of context effects in human subjects.