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 collected rewards in a virtual two-dimensional world. In each trial, we presented two reward options that were either quick to collect but were smaller in value, or took longer to collect but were larger in value. The subjective value of each option was driven by the options' value and how quickly it could be reached. We used this task to investigate three types of potential conflicts: choice ambiguity, choice repetitions, and temporal delay. We manipulated choice ambiguity by varying the subjective values of the decision options. For choice repetition, we biased participants toward one option for two trials and then tested how that affected the subsequent decision. We manipulated 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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