Neural investigation of default effects on decision-making under uncertainty.

Default options have increasingly become a common tool for policymakers in guiding individuals’ behaviors. However, the neural mechanisms of default effects on decision-making, particularly in uncertain situations, remain unclear. In the present study, participants were asked to decide whether to stick with the default options in a gambling task, and their scalp potentials were recorded. The behavioral results indicated that the default effects did exist, given that participants demonstrated a significantly higher likelihood of selecting uncertain payoffs when these were presented as default options, as opposed to when certain payoffs were designated as defaults. The electroencephalography (EEG) data revealed that the assessment of default setting, comparing default uncertain options with default certain options, was reflected not only in early ERP components (such as P200 and MFN) but also in increased activity within the theta frequency band. Certain payoffs elicited larger P200 and MFN amplitudes compared to uncertain payoffs under default settings, and time-frequency analysis revealed greater theta power when the default options involved payoffs (rather than uncertain payoffs). Additionally, ambiguity aversion manifested not only in behavioral tendencies but also in distinct neural signatures, reflected across multiple ERP components associated with early evaluation (such as P200, MFN) and later motivational processing (such as P300, LPP). To further capture how these neural responses relate to behavior, we applied representational similarity analysis (RSA), which revealed that choice patterns were systematically associated with frontal neural activity during an early evaluative stage. Moreover, regression analyses indicated that later-stage neural responses, particularly the LPP, were predictive of individuals’ subsequent uncertainty choices, suggesting that both early evaluation processes and later motivational evaluations contribute to shaping behavior under uncertainty and defaults.