When you need to make a choice but lack sufficient evidence for a solid decision, your brain calculates how much time has elapsed to give you a confidence rating of sorts, says a team of neuroscientists at New York University (NYU). Their findings are published in the journal Neuron.
“In our daily lives, we make many decisions,” says Roozbeh Kiani, Ph.D., an assistant professor in NYU’s Center for Neural Science and one of the study’s authors.
“Sometimes the evidence afforded us is strong, enabling us to decide quickly and accurately. Other times, the evidence is lacking; we take longer to decide and tend to be less accurate. Our brain can learn that longer elapsed times are associated with lower accuracy and should mean less confidence.”
“Our findings show that our brains use this association to calculate confidence, not just based on the available evidence, but also based on how long it takes to gather the evidence.”
It is well known that our decisions typically come with a certain degree of confidence, and this confidence plays a key role in helping us make future choices, especially when the outcomes are delayed and rapid learning is required.
Less understood, however, is how this certainty is established. Researchers have attributed it to two factors: evidence and decision time. If we believe we have enough evidence to make a good decision, for example, we’re more likely to be certain in making a choice. And when it comes to time, the speed of a decision usually reflects confidence — the more quickly we make a choice, the more confident we are.
For the study, researchers asked the participants to determine which way a group of dots were moving (up or down) in a random-dot motion display. Participants answered by making an eye movement to either an up or down horizontal bar, directing their gaze toward one or the other end of the bar to indicate the level of confidence in the decision.
Their results showed that, not surprisingly, more evidence boosted the confidence of responses. Furthermore, the less time it took to make a decision, the more confident the participants felt about their decisions.
“It’s an intriguing notion that the brain might convert its data gathered through the senses into units of ‘degree of belief’ by combining evidence and elapsed time,” said co-author Michael Shadlen, M.D., a professor of neuroscience at Columbia University, an investigator of the Howard Hughes Medical Institute, and a member of Columbia’s Mortimer B. Zuckerman Mind Brain Behavior Institute.
“Those same regularities that support the intuition that time might matter also made it challenging to identify time itself as a player and not just a marker for something else, such as accuracy.
“It makes intuitive sense that ‘time spent’ would serve as a clue about difficulty; proving it in the lab was not easy though. No wonder it took until 2014 to do it!”
Source: New York University