People have described the effect as creepy or eerie, and some have thought it supernatural. But now researchers have demonstrated the very natural cause for this visual effect.
All it takes for the effect to work is to have the person in the painting, or photograph, look straight ahead, said James Todd, co-author of the study and a professor of psychology at Ohio State University. Our visual perception takes care of the rest.
"The core idea is simple: no matter what angle you look at a painting from, the painting itself doesn't change. You're looking at a flat surface. The pattern of light and dark remains the same," Todd said.
"We found that our visual perception of a picture also remains largely unchanged as we look at it from different vantage points. If a person in a painting is looking straight out, it will always appear that way, regardless of the angle at which it is viewed."
The study was conducted at the University of Utrecht in The Netherlands in collaboration with Jan Koenderink, Andrea van Doorn, and Astrid Kappers. Their results were published in a recent issue of the journal Perception.
While scientists have considered the reasons behind this visual effect for more than a century, advances in the field of perception now allow for better ways to study why it occurs, Todd said.
"Researchers have developed powerful techniques that allow us to measure the perception of complex shapes in a very precise way," he said.
In this study, the authors viewed on a computer screen a picture of a medical mannequin human torso in a richly sculpted gilded frame, which appeared to be hanging on a brick wall. The wall and frame were shown in color, the torso in neutral gray.