Why do we see faces in things? Evolution, scientists say

Facial recognition happens at lightning speed in the brain, which is what causes it to see faces where there are none.

This phenomenon is known as pareidolia – the tendency for perception to impose a meaningful interpretation on inanimate objects – and is responsible for people seeing faces in the moon, gnarled wood or even images of Jesus or the Virgin Mary on toast.

Researchers from the University of Sydney say this is a common occurrence, and believe that it is even an evolutionary benefit.

Professor David Alais, the lead author on a new study on how the brain identifies and processes illusory faces, said: “From an evolutionary perspective, it seems that the benefit of never missing a face far outweighs the errors where inanimate objects are seen as faces.

“There is a great benefit in detecting faces quickly, but the system plays ‘fast and loose’ by applying a crude template of two eyes over a nose and mouth.

Throughout human evolution, the brain has developed specialised neural mechanisms to rapidly detect faces using the common facial structure as a shortcut, the study said.

Professor Alais said many things could satisfy this template, adding that facial detection responses were easily triggered, often within a few hundred milliseconds of encountering an object.

“We know these objects are not truly faces, yet the perception of a face lingers.”

“We end up with something strange – a parallel experience that is both a compelling face and an object. Two things at once,” he said.

The study also sought to determine whether the brain discarded illusory faces recognised in inanimate objects or whether the brain continued to analyse the object as though it were a real face.

Participants were presented with a sequence of faces - both real and pareidolia ones - and were asked to rate the expression of each on a scale from happy to angry.

Researchers discovered that once a pareidolia face had been recognised by the brain, it was then analysed for facial expressions in the same way as a real face.

Professor Alais said: “Pareidolia faces are not discarded as false detections but undergo facial expression analysis in the same way as real faces.

“We need to read the identity of the face and discern its expression. Are they a friend or a foe? Are they happy, sad, angry, pained?”

This is because, according to the research, humans are “deeply social beings”. It isn’t enough for the human brain to simply analyse faces, but instead it typically adds emotional attributes to them, the study found.

The study has been published in the Proceedings of Royal Society B and was undertaken in collaboration with scientists at the Laboratory of Brain and Cognition at the National Institute of Mental health in the US.