02 May Certainty in our choices is often a matter of time

Making Decisions: How Time Shapes Confidence

Neuroscientists have discovered that when we lack enough evidence for a decision, our brains use elapsed time as a guide for confidence. Simply put: the longer we take, the less confident we feel, even if accuracy doesn’t change.

Roozbeh Kiani, assistant professor at NYU’s Center for Neural Science, explains:

“Sometimes the evidence is strong, letting us decide quickly and accurately. When evidence is weak, we take longer and tend to be less confident. Our brains learn that longer decision times often mean lower accuracy and factor that into confidence calculations.”

Co-author Michael Shadlen adds:

“The brain converts sensory data into a ‘degree of belief’ by combining evidence and decision time. Time itself acts as a clue about difficulty, not just a marker of accuracy.”

The research shows that confidence—our sense that a choice will succeed—is shaped by both evidence and decision time. Quick decisions usually reflect higher confidence, while longer deliberation can lower it.

In lab experiments, participants judged the direction of moving dots and indicated their confidence through eye movements. Results confirmed that more evidence boosts confidence, but longer decision times reduce it, even when accuracy remains the same.

Kiani concludes:

“Elapsed time plays an independent role in shaping confidence. It provides a computational shortcut but also shows that confidence and accuracy can be dissociated.”

Understanding this can help in designing systems or strategies where decision-making and learning are critical: the more time spent deciding, the lower the perceived confidence.

Research Credits: Roozbeh Kiani (NYU), Michael Shadlen (Columbia University), Leah Corthell (University of Alabama at Birmingham). Supported by Howard Hughes Medical Institute, National Eye Institute, Sloan Research Fellowship, and Simons Collaboration on the Global Brain.