Making a value-based decision is a cognitively complex phenomenon and divisible into several sub-processes, such as the perception, evaluation, and final selection of choice options. Although previous research has attempted to dissociate these processes in the brain, there is emerging evidence that late action selection mechanisms are influenced continuously throughout the entire decision act. We used electroencephalography (EEG) and an established sequential decision making paradigm to investigate the extent to which the readiness potential (RP) and the lateralized readiness potential (LRP), two classic preparatory EEG motor components, reflect the ongoing evaluation process in value-based choices. During the task, human participants sequentially sampled probabilistic information to buy or reject offers of unknown value (using both hands) and were allowed to respond at any time. The pressure to respond was manipulated by charging low or high costs for collecting information. We modeled how and when decisions were made and found that participants adaptively lowered their threshold for required evidence with information costs and elapsed time. These shifts were accompanied by an increased RP-like signal during the decision process. The RP was further influenced by the amount of accumulated evidence. In addition, an LRP could be measured from the start of the decision process, well in advance and independent of the final decision. Our results are consistent with a continuous involvement of the brain's motor system in emerging value-based decisions and advocate using classic EEG motor potentials for studying neurocognitive theories of decision making.
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