The Mysterious Phenomenon of “Pareidolia” Turns Out to Have a Surprising Bias

It’s funny sometimes when your eyes play tricks on you and you see a face that’s not really there, staring at you from a power outlet or a potato. This phenomenon is called facial pareidolia, and it’s something that humans, and even chimpanzees, do naturally.

But it seems facial features aren’t the only thing we see when we encounter an illusory face. A new study has found that we also see age, emotion and gender – and strangely enough, the vast majority of these grimaces are seen as male faces.

“The goal of our study was to understand whether instances of facial pareidolia convey the kinds of social cues that faces normally convey, such as expression and biological sex,” says one of the researchers, Jessica Taubert, researcher in psychology at the University of Queensland.

“Our results showed a striking bias in gender perception, with significantly more illusory faces perceived as male than female.”

The researchers recruited 3,815 participants for an online experiment, asking them to look at more than 200 photos of illusory faces, which the team obtained from the Internet as well as their personal collections (because of course the scientists who study this stuff have personal collections).

Participants were asked to rate the images out of 10 for how easily they could see a face, as well as indicate the emotion they saw in the face, the age range of the face, and gender of the face as “masculine”. ‘, ‘female’ or ‘neutral’.

The contestants saw mostly young faces in the photos – seeing them as either a child or a young adult.

Emotions, on the other hand, were quite varied, with 34% of images perceived as happy, 19% surprised, 19% neutral and 14% angry. A smaller number of faces were perceived as showing sadness, fear or disgust.

Frequency histograms for face, emotion, age and gender. (Wardle et al., PNAS, 2022)

But what really caught the researchers’ attention was that the perceived gender of these faces was overwhelmingly male-biased.

“The magnitude of this gender difference was substantial: 90% of images of illusory faces had an average male rating, while only 9% of images had an average female rating,” the team writes in their new paper.

Perceptual biases like this are quite common. They happen when our brain creates shortcuts to try to understand what we see. Usually we’re pretty good at using these shortcuts to correctly perceive objects, but sometimes, like seeing faces that aren’t actually there, we get it wrong.

“We know that when we see faces in objects, that illusion is processed by parts of the human brain that are dedicated to processing real faces, so in theory face pareidolia ‘tricks the brain,'” says Taubert.

“We now have evidence that these illusory stimuli are processed by the brain by areas involved in social perception and cognition, so we can use facial pareidolia to identify these specific areas.”

facial pareidoliaExamples of pareidolia. (Composite image: Jessica Taubert)

But what is the reason for a perceptual bias that makes illusory faces appear masculine instead of feminine?

Researchers dove deep to find answers. They did more experiments to analyze whether the bias could have been caused by semantic associations of gender, due to object names or items themselves being visually masculine.

They also retested the images, but in grayscale, to see if the colors might have influenced the gender disparity. None of these factors could explain what the researchers saw.

Additionally, the team created gender-ambiguous human face morphs to test whether participants just answered “male” more often when they were unsure of gender. The facial morphs actually showed a little female bias, ruling that out as well.

Finally, they looked at computer modeling to try to reveal whether certain characteristics – such as slanted rather than curved faces – might have caused the gender bias. But the team found that while visual characteristics could explain some of the variance, they could not explain all of the bias.

This means we still don’t know what’s causing the perception bias, but the researchers provide some suggestions.

“One possibility is that it stems from a conceptual or linguistic origin, since masculine is the default gender in social communication. According to this account, the perception of an illusory face in an object invokes the concept of ‘person’, which in turn invokes the concept of ‘masculine’, unless additional information suggests otherwise,” they write in their article.

“A related idea is that male is the default gender of a face, unless other visual details (e.g., eyelashes, long hair, trimmed eyebrows) suggest otherwise… Whatever the origin of the male bias for facial pareidolia, its existence raises interesting questions about how social norms may interact with visual perception.”

The team is looking for other examples of facial pareidolia and can be emailed here.

The research has been published in PNAS.

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