What is surprising about this case is that babies seem to be losing ability with age

Michelle de Haan, UCL

A study by UK scientists at the University of Sheffield and University College London also found that infants can even tell the difference between monkeys.

They believe natural changes in the brain as we grow older may be the reason why adults are not as good at recognising people.

In a paper published in the journal Science, they said the changes might be like those associated with language - our ability to learn new languages decreases with age.

The findings are based on an analysis of brain patterns and eye movements of infants after they were shown a series of pictures of human and monkey faces.

Brain differences

A study of their brain waves found that while infants could distinguish between different monkeys, adults could not.

Similarly, when the pictures were turned upside down babies appeared to still be able to recognise the monkeys.

The scientists then tried another test, this time recording the visual reactions of babies when they were shown a variety of pictures of people and monkeys, some of whom they had seen before.

They found adults took longer to examine new pictures of human faces compared with older faces.

But they looked just as long at the old and new monkey pictures, suggesting they could not distinguish between them.

Surprising findings

In comparison, the six-month-old infants spent significantly longer looking at new pictures of humans and monkeys.

According to the scientists, this suggested that the babies preferred new images and could easily recognise the older pictures be they of humans or monkeys.

Michelle de Haan, one of the study's authors, said the findings were surprising.

She said: "We usually think about development as a process of gaining skills, so what is surprising about this case is that babies seem to be losing ability with age.

"This is probably a reflection of the brain's 'tuning in' to the perceptual differences that are most important for telling human faces apart and losing the ability to detect those differences that are not so useful."