It has been long known that people tend to interpret new information in a way that supports their pre-existing beliefs, a phenomenon known as confirmation bias. Once they’ve decided which house to buy, which school to send their kids to, or which political candidate to vote for, they tend to interpret new evidence such that it reassures them they’ve made the right call. Now, researchers reporting in Current Biology have shown that people will do the same thing even when the decision they’ve made pertains to a choice that is rather less consequential, for example: which direction a series of dots is moving and whether the average of a series of numbers is greater or less than 50?
What the researchers say: “Confirmation biases have previously only been established in the domains of higher cognition or subjective preferences,” says the lead author. “It was rather striking for us to see that people displayed clear signs of confirmation bias when making decisions about more trivial things.”
Although confirmation bias is well known, it wasn’t clear what drives it. Is it that people, after deciding, become less sensitive to new information? Or do they filter new information to reduce conflict with the decision they’ve already made?
To explore this question, the researchers asked study participants to look at two successive movies featuring a cloud of small white dots on a white computer screen. Their task was to report the direction the dots were moving in, which was challenging because these dots were embedded in many more dots that moved about randomly. After the first movie, participants were asked to choose between two options: whether the coherent motion pointed clockwise or counterclockwise from a reference line drawn next to the cloud of dots. After the second movie, they were asked to drag the mouse over the screen to indicate their best continuous estimate of the average direction across both movies they had seen.
The experiments showed that participants, after making an initial call based on the first movie, were more likely to use subsequent evidence that was consistent with their initial choice to make a final judgment the second time around. The finding suggests that the initial choice a person made in the visual motion task acts as a cue, selectively directing their attention to information that’s in agreement with it.
In a second series of experiments, the researchers set a related numerical task. At first, participants were asked to judge whether a series of eight two-digit numbers averaged greater or less than 50. In a second, they were asked to provide a continuous estimate of the average between 10 and 90. Again, participants’ answers showed a pattern of confirmation bias and selective attention.
The researchers say the findings help to identify the source of confirmation biases, with implications for understanding the bounds of human rationality. For those of us attempting to make informed decisions in the real world, the new study offers a reminder.
“Our first impression does not have to be the last impression,” the lead author says. “Such impressions, or choices, lead us to evaluate information in their favor. By acknowledging the fact that we selectively prioritize information agreeing with our previous choices, we could attempt to actively suppress this bias, at least in cases of critical significance, like evaluating job candidates or making policies that impact a large section of the society.”
So, what? This study actually confirms something quite separate from confirmation bias—that we make decisions fast and have a tendency to stick to them. Once again this makes perfect sense in evolutionary terms—if you’re being chased by a lion you don’t stop to reason. If you succeed in escaping your method of escape will become embedded in your subconscious and you’ll tend to rely on it since speed, not reasoning, is of the essence.