Researchers have discovered that people can infer the preferences of others by observing how quickly they make decisions in social scenarios. The study, published in PLOS Biology, reveals that decision-making speed can provide key insights into a person’s social preferences, even when the actual options being considered are unknown.
Humans constantly observe the decisions of others, whether in social settings, professional environments, or everyday life. These observations allow us to infer what other people value, helping to navigate interactions and relationships. Previous studies have shown that we can learn about someone’s preferences based on their decisions. But there’s a missing link in understanding how we gauge not just the choice someone makes, but how strongly they prefer one option over another.
“The study of how people learn from each other has been explored extensively in the past few decades of scientific research: obviously, observing the decisions of other people will give us information about their preferences,” explained Sophie Bavard, a postdoctoral researcher at the Motivation, Brain and Behavior lab at the Paris Brain Institute. (She conducted the research while at the University of Hamburg.)
“Yet, while most of the literature so far focused only on observing choices, we also know that choices alone are not the sole output of a decision: the decision speed, for example, will convey additional information. Therefore, we aimed at filling this gap and investigated whether people can learn others’ preferences from observing their decision speed instead of their final choice — and if yes, to which extent.”
To investigate this, the researchers used a version of a well-known psychological experiment called the Dictator Game. This game involves two participants: one, the “dictator,” is given a sum of money and must decide how much to keep and how much to give to another anonymous participant. This setup creates a situation where the dictator’s decisions reflect their social preferences—whether they are selfish and keep more for themselves, or more prosocial, choosing to share fairly.
The research team recruited 16 participants to act as dictators. Each dictator completed a series of trials in which they had to choose between two different ways of splitting the money. These options varied in how much they favored the dictator versus the other person. Importantly, the time it took for each dictator to make their decisions was recorded, providing a measure of their decision-making speed.
A second group of 46 participants, referred to as observers, was then recruited. These observers were tasked with watching the decision-making of the dictators. However, in a twist, they were sometimes only shown how long the dictators took to decide, without seeing the actual decisions they made.
The researchers used a design that manipulated the information available to the observers in four different conditions:
- In one condition, observers saw both the choices and the decision times.
- In another, they saw only the decision times.
- A third condition revealed only the choices.
- In the final condition, neither choice nor time was shown.
The observers were asked to estimate the dictator’s social preferences—whether they leaned more toward selfish or prosocial behavior.
Observers performed best when they could see both the choices and the decision times together. In these cases, decision time seemed to reinforce the meaning of the dictator’s choice, allowing observers to make more refined judgments. For example, a fast decision combined with a selfish choice signaled a strong preference for self-interest, while a slower decision suggested that the dictator might have been considering a more balanced or prosocial option. This shows that decision time serves as a useful complementary cue when available alongside the actual choices.
However, when observers were shown only the decision time, they still managed to make accurate judgments. Short decision times were interpreted as a sign of strong preferences, either selfish or prosocial, while long decision times indicated that the dictator was more conflicted or undecided. Even without seeing the choices, observers could gauge the dictator’s likely preferences based on how long they deliberated.
The study also indicated that observers were able to predict the dictators’ future choices after learning about their preferences through decision time or choice observation. Interestingly, when observers predicted future decisions, their response times mirrored the decision times of the dictators they had observed. This suggests that observers internalized the decision-making difficulty of the dictators, effectively putting themselves in the other person’s shoes.
“Imagine a friend having to choose between pizza or pasta, or between a cocktail or a soda: you can predict what they prefer by knowing how long it takes them to make a choice,” Bavard told PsyPost. “The social advantage humans gain from taking others’ decision time into account on top of their choice has been established in the literature already, but here we go a step further by showing that decision time alone is sufficient to learn about others’ preferences. This key result highlights the relevance of considering decision times, for example in tabletop games, where people can strategically manipulate their decision time without disclosing their choices or strategies.”
“More broadly, decision times have an impact in many real-life situations where a friend of ours must choose between two options (e.g., food, entertainment, political candidates…). Before we see their final choice (and, indeed, even if we do not know their final choice), their decision time alone will be quite revealing, as seeing them hesitating would probably signal that they don’t have a strong preference (e.g., they are not picky with their fast-food and pizza is not much more appealing than pasta), or aren’t familiar enough with the available options to have a clear ranking (e.g., they simply don’t consume fast-food very often).”
“Ultimately, by observing people make choices across multiple situations and domains, we may even make inferences about their general personality or decision-style, for instance that a particular friend is generally an indecisive person,” Bavard explained. “Such inferences are crucial for daily social interactions and our results highlight a possible way in which they can happen.”
Interestingly, even when neither the choice nor decision time was visible, observers still performed slightly better than chance at estimating preferences. This suggests that people often rely on general assumptions about how others might behave, even in the absence of concrete information.
While the study provides evidence that people can infer social preferences based on decision time, there are some limitations to consider. First, the study was conducted in a controlled lab environment using a simplified decision-making game. In real-world settings, decisions are often more complex, influenced by a wider range of factors, and may not follow the same patterns as those observed in the lab.
“To the best of our knowledge, we are the first group to empirically test whether or not humans could learn other people’s social preferences from observing their decision times alone,” Bavard said. “With this successful result in hand, the story does not end here: an interesting follow-up experiment would be to test whether the same effect would hold in different social games settings, outside the dictator game.”
“We are now working on replicating the results of this study in a more difficult (and, perhaps more ecologically valid) setting. In the long term, now that we know that people can learn from decision times alone, we are interested in uncovering the finer details and perhaps even the biological underpinnings of this learning. We are currently developing an imaging study with brain recordings, to dig deeper into the underlying mechanisms of this fascinating learning process.”
The findings have broad implications for understanding social cognition and decision-making. They suggest that decision speed is not just a byproduct of decision-making but an integral part of how people infer preferences and predict future behavior.
“In this study, we also propose a novel observational learning model that closely matches participants’ behavior,” Bavard added. “In contrast to previous literature suggesting that people should be able to learn equally well from choices and decision times, we formally show that observers’ behavior substantially deviates from this prediction, since people learned less efficiently than an optimal learning model would.”
“Thus, our study provides a mechanistic account for people’s ability to learn from others’ decision times, while at the same time illustrating that this ability has certain limitations. Naturally, these findings are relevant for future modelling efforts of how people learn from each other. By incorporating decision times into models, we can make more accurate predictions of human behavior, as decision times provide a continuous measure that reveals the strength of these preferences, offering a more detailed perspective.”
The study, “Humans can infer social preferences from decision speed alone,” was authored by Sophie Bavard, Erik Stuchlý, Arkady Konovalov, and Sebastian Gluth.
