Mid-frontal theta is a sensitive marker for cognitive conflict. However, most research focuses on cognitive control paradigms (e.g., the Flanker task). Here, we ask if mid-frontal theta is also sensitive to response conflicts within value-based decision-making. We recorded electroencephalography activity during a value-based binary decision task. In this task, participants collect rewards in a virtual two-dimensional world. In each trial, we present two reward options that are either quick to collect but are smaller in value, or take longer to collect but are larger in value. The subjective value of each option is driven by the options' value and how quickly they can be reached. We used this task to investigate three types of potential conflicts: choice ambiguity, choice repetitions, and temporal delay. We investigated choice repetition by biasing participants toward one option for two trials and then testing how that affects the subsequent decision. We manipulated choice ambiguity by varying the subjective values of the decision options, and temporal delay by making one option quick to collect and one longer to collect. The behavioral results showed the expected effects: Decision times were shorter for unambiguous choices, participants showed a tendency to repeat the previous choice and decision times were shorter for repetitions, and decision times were shorter for earlier available choices. Response-locked mid-frontal theta power was increased for choice switches as compared to choice repetitions, and for the later available as compared to the earlier available option, but we found no effect of ambiguity.

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