London, June 3 (IANS): A key element of infant brain development occurs years earlier than previously thought, scientists have discovered.

The way we perceive faces - using the right hemisphere of the brain -- is unique and sets us apart from non-human primates.

It was thought this ability develops as we learn to read, but researchers from the University of Louvain in Belgium found that in babies as young as four months, it is already highly evolved.

"Just as language is impaired following damage to the brain's left hemisphere, damage to the right hemisphere can impair our ability to distinguish faces so it is critical to understand how it develops," said study co-author Bruno Rossion, principal investigator at the University of Louvain.

Researchers used a cap fitted with electrodes to monitor the brain activity of 15 babies as they sat on their mothers' laps and watched a rapid succession of images over 20 seconds.

They were shown 48 images of faces that differed in viewpoint and colour, interspersed with 200 images of animals, plants and man-made objects.

Each image was shown for only 166 milliseconds, the same rate used for adult studies.

Compared to other images, the appearance of a face was shown to coincide with a specific spike in stimulation of the right hemisphere of the brain.

The difference between the right and the left hemisphere was even more pronounced than in the same study with adults, confounding previous assumptions.

"Given the enormous resources devoted to digital face recognition, the babies' brain accomplishment is not trivial," Rossion said.

The success of this research method in babies demonstrates that it can be used in all ages to improve our understanding of how we develop the ability to perceive complex images.

The study was published in the journal eLife.