DECISION-MAKING INDUCES INFORMATION REDUCTION

Decision-making is usually viewed as a valuation process of choice options followed by a read-out subserving action selection. We hypothesized that action selection is not merely a read out but alters valuation. We investigated whether and how selecting an option among several ones alters option valuations guiding selection. Through computational modeling and behavioral experiments, we found selection-based distortions in evidence-based belief representations guiding selection. More precisely, we found that option selection leads to equalizing evidence-based beliefs across the unchosen options (belief equalization effect) while maintaining the evidence-based belief supporting the actual choice. By contrast, selecting options based on external cues unrelated to evidence-based beliefs induced no belief distortions including equalization effects across the unchosen options but inflated the belief of the chosen option (belief inflation effect). fMRI data confirm that while the pre-Supplementary Motor Area and the dorsal Anterior Cingulate Cortex subserve action selection deriving from evidence-based beliefs encoded in the inferior parietal cortex bilaterally, these inferior parietal representations of evidence-based beliefs underwent belief equalization effects bilaterally. These results reveal that action selection is not only a read-out of decision variables resulting from valuation processes but does alter the decision variables through reducing encoded information that drives selection.