following the crowd as a shortcut

a game you can’t fully see

imagine you’re at a trailhead in another country. the signs list each trail’s distance and difficulty, but you can’t read them. the trails are color-coded, though, and you see two hikers ahead of you take the red one. which would you take?

the game on the right works the same way. you’ll choose between a red gamble and a blue one, and you’ll always see which color two other players picked. some gambles are clear, and some are fogged over.

a choice that’s hard to judge

the fog in the game is an analogy. the participants in our study could read the gambles just fine, but some of them had damage to brain areas that help weigh risk, which can make judging those gambles harder. we wanted to know whether they would rely more on other people’s choices.

we studied participants with damage to one of two regions that help weigh risk: the insula and the dorsal anterior cingulate cortex (dACC). the damage came from brain surgery they’d had before joining the study, and the maps on the right show where each group’s damage overlapped. like you, they chose between safer and riskier gambles, sometimes alone and sometimes after seeing two other players’ choices.

next: choices from 28 healthy adults, 10 people with insula damage, and 6 with dACC damage.

two ways another person’s choice can sway you

another person’s choice can sway you in two ways. it can make that option seem more valuable to you (what we called ‘other-conferred utility’ in our study of teens), or you can simply copy it without weighing the option yourself (‘following’).

how did we tell these apart? we used a computational model, a series of equations with parameters that are fit to each participant’s choices, that estimates how much each strategy drove their decisions, alongside their own ‘risk preference’. in the plot on the right, each dot is one participant, and higher means they relied more on following.

the height is the model’s ‘following weight’, not the share of times someone copied.

the lesion groups copied more

both lesion groups relied on following more than the healthy adults did. the grey circles are the group averages.

now look at the individual dots. many healthy adults also relied on following, and every group varies a lot. studying the lesion groups helped us identify a strategy that shows up, to some degree, in everyone’s choices.

harder solo choices, more copying

now the dots move sideways. left to right shows how well each participant’s solo choices, made without seeing anyone else, were explained by their own risk preferences (we call this ‘solo mismatch’). farther right means a worse fit: their own risk preferences explained their choices less well.

the line slopes up: participants whose solo choices were harder to explain from their own risk preferences relied more on following when they had the chance. in other words, following others may fill the gap when your own evaluation of the options isn’t giving you a clear answer.