Scientists have found that when facial features are difficult to recognise, people readily use information about someone's body to identify them, without being aware that they are doing so.
"Psychologists and computer scientists have concentrated almost exclusively on the role of the face in person recognition," said lead researcher, Allyson Rice of the University of Texas at Dallas.
"But our results show that the body can also provide important and useful identity information for person recognition," Rice said.
In several experiments, the researchers had college-age participants look at images of two people side by side and identify whether the images showed the same person or different people.
Some of the image pairs looked similar even though they actually showed different people, while others looked different even though the pictures showed the same person.
The image pairs were chosen this way so that the information provided by the subjects' faces was ambiguous and not very helpful in determining the subjects' identity, based on a computer face recognition system's performance with these image pairs.
The researchers edited the pictures in several of the experiments, omitting the subjects' bodies or faces to determine which features were most important for successful identification.
Overall, participants were able to accurately discern whether the images showed the same person when they were provided complete images. And participants were as accurate in identifying image pairs in which the faces were blocked out and only the bodies were shown.
But accuracy dropped off when participants saw images that included the subjects' faces but not their bodies. Participants stated afterwards that they used the nose, face shape, ears, mouth, and eyes as tools for identifying even though their results suggested otherwise.
"This left us with a paradox. The recognition data clearly indicated the use of body information for identification. However, the subjective ratings suggested that participants were unaware of how important the body was in their decision," researchers said.
Researchers used eye-tracking equipment to determine where participants were actually looking while identifying the images, and the results showed that participants spent relatively more time looking at the body when the face did not provide enough information to identify the subjects.
By showing that humans don't just rely on faces to identify others, researchers said the study opens up new avenues for developing and refining computer-based recognition systems. The findings are published in Psychological Science.