Anyone can see the face of Jesus on a slice of toast, a rocky face on Mars, or a man in the moon. But although seeing nonexistent faces is generally quite common, some people may be more likely than others to experience the phenomenon: personality, sex, and emotional state may influence our tendency to perceive faces and other meaningful patterns when they don't actually exist, according to new research presented earlier this month at the 19th annual meeting of the Association for the Scientific Study of Consciousness in Paris.

This phenomenon, called pareidolia, occurs as a result of how the brain works. One area of the brain, called the right fusiform face area, is specialized to process true faces, and the same area also activates when people see a face pattern inside noise. This universal experience has led to countless photographs, a $28,000 sale of an old grilled cheese sandwich, and was famously exploited by the Swiss psychologist Hermann Rorschach to develop his inkblot test, which is still used today to gauge the mental state of psychiatric patients or examine personality traits of anyone in general.

In the new study, Norimichi Kitagawa of the NNT Communication Science Laboratory in Tokyo and his colleagues designed an experiment to test whether one's personality traits and emotional state can affect the tendency to experience pareidolia, and the characteristics of the pareidolic images that people experience might predict their personality and emotional state.

The researchers recruited 166 healthy undergraduate students and asked them to complete the Ten Item Personality Inventory and the Positive and Negative Affect Scale, questionnaires designed to assess the 'big five' personality traits and emotional mood, respectively. They showed all the participants the same pattern of random dots, asking them to report whatever shapes they saw within it, and also to trace the shapes they saw onto the pattern with a pen.

They found that some of the participants had a greater tendency than others to perceive meaningful shapes in the random pattern of dots – including not only faces, but also animals and plants – and that this tendency was correlated with particular traits and moods.

Overall, those with a higher neuroticism score were more likely to experience pareidolia, as were those who reported being in a less negative mood. But that the physical characteristics of the pareidolic images they perceived was not related to the participants' personality traits or emotional states. The researchers also found that women were more likely than men to experience pareidolia.

Exactly why certain traits might make one more susceptible to pareidolia is still unclear, but Kitagawa and his colleagues propose that an evolutionary purpose may have been behind women's higher tendency for pareidolia. Females are often physically weaker than males, and this, the researchers say, may have made them more sensitive to meaningful stimuli within noise, better enabling them to detect predators in a forest.

Neurotic people tend to be less emotionally stable than others, and this, too, may make them tend to see meaningful patterns that aren't actually there. Likewise, certain moods may increase the tendency to see such patterns. "We think positive moods enhance creativity," says Kitagawa, "so people with higher positive mood scores may find more possible interpretations of the dots."