How Our Brain Judges Trustworthiness in Milliseconds

It’s often said that we can make a judgement about a person within seconds of meeting them, and that this judgement is often remarkably accurate.  A new study highlights just how valuable this skill is, in particular in determining how trustworthy someone is.

“The results are consistent with an extensive body of research suggesting that we form spontaneous judgments of other people that can be largely outside awareness,” reveals author Jonathan Freeman, an assistant professor in New York University’s psychology department.

The focus of the researchers analysis was the amygdala region of the brain, which neuroscientists believe to be the key for many of our social and emotional behaviours.  This area has been highlighted in previous studies as crucial for forming our beliefs about the trustworthiness of someone we meet.  What we haven’t known, until now, however is just how quickly this part of the brain goes about its work. This new study suggests that it works incredibly quickly, and indeed can build its perception of someone in literally the blink of an eye, usually without us even realising it.

the amygdala region of the brain processes trustworthiness features without us being consciously aware of it

To test this out, the researchers conducted a couple of experiments during which participants were asked to view a series of facial images whilst their amygdala was scanned for any activity.

The photos contained a combination of real pictures of actual strangers faces and some artificially generated faces that had various trustworthiness cues manipulated to appear more or less trustworthy.  These cues were based upon prior research into trustworthiness, and included things such as higher inner eyebrows (towards the top of the nose) and prominent cheekbones, both of which have been identified as particularly trustworthy features.

Participants in the study were placed inside a brain scanner and shown each face one by one.  So far, so normal, except that each photo would only be shown to the participants for a small period of time.  We’re talking milliseconds here.  In other words, it was so quick that it would only be captured subconsciously by the brain.  To ensure this was the case, the researchers also used a technique known as backward masking.

Backward masking is a process that tries to ensure the brain ends one task and begins another afresh.  In this instance, a second photo was shown straight after the first photo was flashed before each participant.  This second image is believed to halt the brain’s ability to process the original image any more than it currently had, thus stopping it from obtaining a conscious awareness of it.

Both experiments showed activity in specific areas of the amygdala whenever the participants were attempting to mesure the trustworthiness of a face.  Different parts of the amygdala would come to life however when the participant was trying to judge the strength of the signal.  All of this activity was taking place despite the participant being unaware that they’d even seen a face!

“These findings provide evidence that the amygdala’s processing of social cues in the absence of awareness may be more extensive than previously understood,” Freeman states.

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