In a order to identify a face, our brain first looks at eyes and then shifts to the shape of the mouth and nose, concludes a new study. The research by the University of Barcelona (UB) has analysed which facial features our brain examines to identify faces.
The objective of the study, undertaken by researcher Matthias S. Keil from the Basic Psychology Department of the UB and published in the prestigious US journal PLoS Computational Biology, was to ascertain which specific features the brain focuses on to identify a face.
It has been known for years that the brain primarily uses low spatial frequencies to recognise faces. "Spatial frequencies" are, in a manner of speaking, the elements that make up any given image.
As Keil confirmed to SINC, "low frequencies pertain to low resolution, that is, small changes of intensity in an image. In contrast, high frequencies represent the details in an image. If we move away from an image, we perceive increasingly less details, that is, the high spatial frequency components, while low frequencies remain visible and are the last to disappear."
"In order to identify a face in an image, the brain always processes information with the same low resolution, of about 30 by 30 pixels from ear to ear, ignoring distance and the original resolution of the image," Keil says.
"Until now, nobody had been able to explain this peculiar phenomenon and that was my starting point,” the expert added.
What Matthias S. Keil did was to analyse a large number of faces, namely those belonging to 868 women and 868 men.
"The idea was to find common statistical regularities in the images," the expert said.
Keil used a model of the brain''s visual system, that is, "I looked at the images to certain extent like the brain does, but with one difference: I had no preferred resolution, but considered all spatial frequencies as equal. As a result of this analysis, I obtained a resolution that is optimum in terms of encoding, as well as the signal-to-noise ratio, and was also the same resolution observed in the psychophysical experiments".
The result therefore suggests that faces are themselves responsible for our resolution preference.
This led Keil to one of the brain''s properties: "The brain has adapted optimally to draw the most useful information from faces in order to identify them. My model also predicts this resolution if we take into account the eyes alone – ignoring the nose and the mouth – but also by considering the mouth or nose separately, albeit less reliable."
Therefore, the brain extracts key information for facial identification primarily from the eyes, while the mouth and the nose are secondary, according to the study.