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People Trust Strangers who Look Much Like an Old Friend

Photo By Antonio Guillem via Shutterstock


Parents have cautioned their children not to trust strangers, but there are people who, despite being unknown to us, still manage to get our trust. Experts attribute it to the stranger likely looking much like an old friend.

New York University researchers conducted a series of experiments to test that theory, Health Day reported. They found that the participants in a new study were more likely to select the photos of strangers who have a strong resemblance to honest people they had met. The volunteers did not select photos of strangers who reminded them of dishonest people they encountered in a previous game.

Unaware of the resemblance

However, Elizabeth Phelps, a professor at the Department of Psychology in NYU, pointed out that the participants who made decisions about the reputation of a stranger without any direct or explicit information were picked even if the volunteers were not aware of the resemblance. She said that it showed the human brains deploy a learning mechanism in which moral information encoded from past experience guided future choices.

Oriel FeldmanHall, the leader of the study, said that the research revealed that strangers are distrusted even if their resemblance to someone previously associated with immoral behavior was minimal. She compared the similarity to Pavlov’s dogs.

The dog, even if it was conditioned on a single bell, continues to salivate to bells that have similar tones. In this case, FeldmanHall said that people use information about the moral character of a person as a basic Pavlovian learning mechanism to make judgments about strangers. The information, in this case, is if the stranger can be trusted.

The study, published in the Proceedings of the National Academy of Sciences, showed how the human brain functions in making decisions when interacting with strangers. Past studies have provided researchers with a better grasp on how social decision-making unfolds in repeated one-on-one interactions.

Trust game

To explore how the brain functions in the decision-making process involving strangers, the researchers held several experiments that focused on a trust game. The game had the participants make several decisions about the trustworthiness of their partners. They must decide if they can entrust their money to three different players represented by facial images, Eureka Alert reported.

The 29 participants had the choice of keeping $10 or investing all or part of it with one of three men they did not know but were shown photos, the Guardian reported.

The participants were aware that the money they invested would be multiplied four times, and the other player can share the money back or keep the money for himself. The three players were highly trustworthy who reciprocated 93 percent of the time, somewhat trustworthy who reciprocated 60 percent of the time, and not at all trustworthy who reciprocated only 7 percent of the time.

For the second task, the volunteers were asked to pick new partners for another game. But unknown to them, the partners were the same people but their faces were morphed to varying degrees. Only one of the three original players had the same physical resemblance to the previous ones.

Although the participants were not aware that the strangers closely resembled the faces of those they previously encountered, it turned out that the volunteers preferred to play with strangers who had a resemblance to the original player that they played with who was considered trustworthy. They avoided playing with strangers who resembled an earlier untrustworthy player.

The decision to trust or distrust a stranger revealed an interesting and sophisticated gradient. The increase in trust steadily rises the more the stranger looked like a trustworthy partner from a previous experiment. It also steadily decreased the more the stranger bore a resemblance to the untrustworthy player.


Examining the brain activity

The researchers, in a subsequent experiment, studied the brain activity of the participants as they made the decisions. They discovered that when the volunteers decided if the stranger can be trusted or not, the brains tapped the same neurological region that was involved when learning about the partner in the first task. It included the amygdala, the region that plays a bigger role in emotional learning. The study found that the greater the similarity in neural activity between initially learning about an untrustworthy player and deciding to trust a stranger, the more subjects refused to trust the stranger.

The authors said that the results of the study illustrate the highly adaptive nature of the brain because it shows that we make moral assessments of strangers drawn from previous learning experiences.

Antonio Espin, a behavioral economist from Middlesex University in London, said the implications of the research can be wide-ranging. He noted that the since the main reason for the facial similarity is shared genes, the study not only advanced people’s understanding of why we trust or not trust specific strangers. It also has broader implications for ethnic or racial discrimination and in the evolutionary arena of partner selection.

[메디컬리포트=​Vittorio Hernandez 기자]

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