People tend to perceive faces they are familiar with as looking happier than unfamiliar faces, even when the faces actually express the same emotion to the same degree, says a study.
"We show that familiarity with someone else's face affects the happiness you perceive in subsequent facial expressions from that person," said Evan Carr of Columbia Business School, Columbia University in New York City.
"Our findings suggest that familiarity - just having 'expertise' with someone else's face through repeated exposure - not only influences traditional ratings of liking, attractiveness, etc. but also impacts 'deeper' perceptions of the actual emotion you can extract from that person," Carr said.
The fact that people tend to prefer things they are familiar with - whether people, objects, or other stimuli - has been demonstrated many times in research studies, in many different ways.
But a fundamental question remains: Why do we prefer familiar things? Is it knowing that something is familiar that engenders positive feelings? Or could it be that familiarity actually leads us to perceive stimuli more positively?
The researchers hypothesised that familiarity might guide our fundamental perceptual processes in a bottom-up fashion, selectively enhancing the positive features of a stimulus.
To test this hypothesis, they designed two experiments that examined how people responded to familiar and unfamiliar faces.
In the first experiment, the researchers morphed images of male and female faces to create faces that varied in the type and degree of emotion expressed.
This process resulted in a continuum of morphed faces that ranged from 50 per cent angry to neutral to 50 per cent happy. The researchers then divided the images into two sets.
The researchers then familiarised the participants with some faces.
Participants were more likely to identify the familiar face as the happier one in the pair, despite the fact that the faces showed the same emotion to the same degree, the findings, published in the journal Psychological Science, showed.
And they were increasingly more likely to choose the familiar face as the positive features in the faces increased.
In a second experiment, Carr and colleagues asked 40 undergraduate participants to look at a series of faces and decide whether each face was either "happy or angry."
The results replicated those of the first experiment. Participants were more likely to identify familiar faces as happy compared with unfamiliar ones, but only when the faces were emotionally neutral or positive.