Confirmation bias through selective readout of information encoded in human parietal cortex

TL;DR

People ignore information that contradicts their beliefs, even though the brain accurately encodes it.

Contribution

The study shows that contradicting information is encoded in the brain but not used in decisions.

Findings

Information contradicting beliefs is encoded in the parietal cortex.

Such information has little impact on behavior despite accurate encoding.

Confirmation bias arises from selective use of encoded evidence.

Abstract

Decision-makers often process new evidence selectively, depending on their current beliefs about the world. We asked whether such confirmation biases result from biases in the encoding of sensory evidence in the brain, or alternatively in the utilization of encoded evidence for behavior. Human participants estimated the source of a sequence of visual-spatial evidence samples while we measured cortical population activity with magnetoencephalography. Halfway through the sequence, participants were prompted to judge the more likely source category. We find that processing of subsequent evidence depends on its consistency with the previously chosen category. Evidence encoded in parietal cortex contributes more to the estimation report when that evidence is consistent with the previous choice compared to when it contradicts that choice. Our results indicate that information contradicting pre-existing beliefs has little impact on subsequent behavior, despite being precisely encoded in the brain. This provides room for deliberative control to counteract confirmation biases.

People often discard incoming information when it contradicts their pre-existing beliefs about the world. Here, the authors show that this discarded information is precisely encoded in the brain, but has little impact on subsequent behavior.

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