Choice Certainty Is Informed by Both Evidence and Decision Time

• Published in: Neuron (Cambridge, Mass.) Vol. 84; no. 6; pp. 1329 - 1342
• Main Authors: Kiani, Roozbeh, Corthell, Leah, Shadlen, Michael N.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 17.12.2014; Elsevier Limited
• Subjects: Accuracy; Choice Behavior - physiology; Decision making; Eye Movements - physiology; Female; Humans; Hypotheses; Motion Perception - physiology; Photic Stimulation; Reaction Time - physiology; Scholarships & fellowships; Uncertainty; Young Adult
• ISSN: 0896-6273; 1097-4199; 1097-4199
• DOI: 10.1016/j.neuron.2014.12.015

“Degree of certainty” refers to the subjective belief, prior to feedback, that a decision is correct. A reliable estimate of certainty is essential for prediction, learning from mistakes, and planning subsequent actions when outcomes are not immediate. It is generally thought that certainty is informed by a neural representation of evidence at the time of a decision. Here we show that certainty is also informed by the time taken to form the decision. Human subjects reported simultaneously their choice and confidence about the direction of a noisy display of moving dots. Certainty was inversely correlated with reaction times and directly correlated with motion strength. Moreover, these correlations were preserved even for error responses, a finding that contradicts existing explanations of certainty based on signal detection theory. We also contrived a stimulus manipulation that led to longer decision times without affecting choice accuracy, thus demonstrating that deliberation time itself informs the estimate of certainty. We suggest that elapsed decision time informs certainty because it serves as a proxy for task difficulty. •Certainty in a decision is guided by accumulated evidence and decision time•A manipulation that prolongs decisions without affecting accuracy reduces certainty•Certainty in an error is greater for easier stimuli, because the decision is faster•Bounded evidence accumulation explains decision accuracy, speed, and certainty When we decide, we possess a graded certainty that we are correct. Kiani et al. show that the brain measures the time it takes to reach a decision and uses this elapsed time to calibrate certainty.