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Pupil size can be mimicked, according to a new study.

New research reveals that pupil mimicking boosts trust. However, the latest finding has only been proven among people of the same ethnicity.

"People generally underestimate the importance of pupils, despite the fact that we look into them each day. The pupil provides a rich source of social information -- we can force a smile, but we can't force our pupils to dilate or constrict," says psychological scientist Mariska Kret of Leiden University, lead author on the study. "Our findings show that humans synchronize their pupil size with others and this behavior -- over which we have no voluntary control -- influences social decisions."

The latest study involved 61 students from a Dutch university. The participants were asked to view short video clips of their partners. Participants then had to decide whether to transfer 5 Euros or 0 Euros. The participants were told that their investment would be tripled, and that their partner would decide the portion to give back to the participant.

However, participants didn't know that the video clip was actually a manipulated image of a pair of eyes that were programmed to dilate, constrict or remain static over a span of four seconds.

The findings revealed that participants were more likely to trust partners whose pupils had dilated. Furthermore, eye tracking data revealed that participants were significantly more likely to mimic their partners' pupils, whether they were dilating or constricting. Study results participants who mimicked their partner's dilating pupils were more likely to decide to invest money. However, this was only true when the partner had a Western European appearance.

"The results of the current study further confirm the important role for the human eye in what people love and fear," researchers wrote.

"More specifically, pupil mimicry is useful in social interactions in which extending trust and detecting untrustworthiness in others go hand in hand, and it benefits in-group interactions, survival, and prosperity," they concluded.

The findings are published in the journal Psychological Science.