While psychologists have long known that first impressions are important in determining how people are perceived by others, researchers are now saying that a person’s sexuality can also be determined by just a glance.

Researchers from the University of Washington found that people have an inbuilt ‘gaydar’ which gives them to ability to judge in the blink of an eye whether others are gay or straight, according to a study published in the online Public Library of Science.

They also found people are better at judging a woman’s sexuality than a man’s from just a glance.

The study consisted of 129 students who were shown 96 different black-and-white photos of gay and straight men and women.  After participants were briefly shown each picture for less than a second, researchers asked the participants to guess the sexuality of the person in the photograph. 

Researchers noted that the pictures were just faces and were cropped so that hairstyles were not visible.  Researchers did not use photographs of people with facial hair, glasses and makeup to prevent ‘easy cues’.

Researchers reported that participants were able to accurately determine if a woman was gay or straight in two-thirds of the cases and accurately judged 57 percent of the men they saw.

The findings suggest that people unconsciously make decisions about whether someone is gay or straight every time they meet a new person.

“It may be similar to how we don't have to think about whether someone is a man or a woman or black or white,” said researcher Joshua Tabak, a psychology student at the University of Washington, the Daily Mail reported.

“This information confronts us in everyday life,” Tabak added.

Even when faces in the photographs were turned upside-down, participants were able to accurately guess the sexuality of the people in the pictures, according to the study.

However, not everyone is equipped with a ‘gaydar’. 

Tabak noted that there was “always a small number of people with no ability to distinguish gay and straight faces,” in his experiments.

“People from older generations or different cultures who may not have grown up knowing they were interacting with gay people” and could therefore be less accurate in making gay versus straight judgments, he explained.