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It鈥檚 so commonplace we barely give it a second thought, but human brains seem hardwired to see human faces where there are none 鈥� in objects as varied as the moon, toys, plastic bottles, tree trunks and vacuum cleaners. Some have even seen an imagined Jesus in cheese on toast.

Until now scientists haven鈥檛 understood exactly what the brain is doing when it processes visual signals and interprets them as representations of the human face.

Neuroscientists at the University of Sydney now say how our brains identify and analyse real human faces is conducted by the same cognitive processes that identify illusory faces.

鈥淔rom an evolutionary perspective, it seems that the benefit of never missing a face far outweighs the errors where inanimate objects are seen as faces,鈥� said Professor聽David Alais lead author of the study from the School of Psychology.

鈥淭here is a great benefit in detecting faces quickly but the system plays 鈥榝ast and loose鈥� by applying a crude template of two eyes over a nose and mouth.

"Lots of things can satisfy that template and thus trigger a face detection response.鈥�

This facial recognition response happens lightning fast in the brain: within a few hundred milliseconds.

鈥淲e know these objects are not truly faces, yet the perception of a face lingers,鈥� Professor Alais said.

鈥淲e end up with something strange: a parallel experience that it is both a compelling face and an object. Two things at once. The first impression of a face does not give way to the second perception of an object.鈥�

This error is known as 鈥渇ace pareidolia鈥�. It is such a common occurrence that we accept the notion of detecting faces in objects as 鈥榥ormal鈥� 鈥� but humans do not experience this cognitive process as strongly for other phenomena

The brain has evolved specialised neural mechanisms to rapidly detect faces and it exploits the common facial structure as a short-cut for rapid detection.

鈥淧areidolia faces are not discarded as false detections but undergo facial expression analysis in the same way as real faces,鈥� Professor Alais said.

Not only do we imagine faces, we analyse them and give them emotional attributes.

The findings are published in the聽.

The researchers say this expression analysis of inanimate objects is because as deeply social beings, simply detecting a face isn鈥檛 enough.

鈥淲e 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?鈥� Professor Alais said.

What the study examined was whether once a pareidolia face is detected, it is subsequently analysed for facial expression, or discarded from face processing as a false detection.

The research shows that once a false face is retained by the brain it is analysed for its facial expression in the same way that a real face is.

鈥淲e showed this by presenting sequences of faces and having participants rate each face鈥檚 expression on a scale ranging from angry to happy,鈥� Professor Alais said.

What was intriguing is that a known bias in judging human faces persisted with analysis of inanimate imagined faces.

础听previous study undertaken聽by Professor Alais showed that in a Tinder-like situation of judging face after face, a bias is observed whereby the assessment of the current face is influenced by our assessment of the previous face.

The scientists tested this by mixing up real faces with pareidolia faces 鈥� and the result was the same.

鈥淭his 鈥榗ross-over鈥� condition is important as it shows the same underlying facial expression process is involved regardless of image type,鈥� Professor Alais said.

鈥淭his means that seeing faces in clouds is more than a child鈥檚 fantasy,鈥� he said.

鈥淲hen objects look compellingly face-like, it is more than an interpretation: they really are driving your brain鈥檚 face detection network. And that scowl, or smile; that鈥檚 your brain鈥檚 facial expression system at work. For the brain, fake or real, faces are all processed the same way.鈥�

The study was undertaken in collaboration with scientists at the聽聽at the National Institute of Mental Health in the United States.