Babies find it easier to learn words with repetitive syllables rather than mixed sounds, a study suggests.

Assessments of language learning in 18-month-olds suggest that children are better at grasping the names of objects with repeated syllables, over words with non-identical syllables.

Researchers say the study may help explain why some words or phrases, such as 'train' and 'good night', have given rise to versions with repeated syllables, such as choo-choo and night-night.

The researchers say such words are easier for infants to learn, and may provide them with a starter point for vocabulary learning.

A team from the University of Edinburgh assessed the infants' language learning behaviour in a series of visual and attention tests using pictures on a computer screen of two unfamiliar objects.

The two objects were named with made-up words which were communicated to the infants by a recorded voice - one with two identical syllables, for example neenee, and the other without repeated syllables, such as bolay.

The infants were then tested for their recognition of each made-up word. Recordings of their eye movements showed they looked more reliably at the object labelled with repeated syllables, than the other object.

Researchers validated their results with a control test, in which the infants responded to pictures of familiar objects - such as a dog or an apple.

Previous studies show that infants more easily learn patterns involving repetition in visual sequences and musical notes. Researchers say these latest findings show that this tendency also applies to word learning.

Lead researcher Mitsuhiko Ota, of the University of Edinburgh's School of Philosophy, Psychology and Language Sciences, said: "This is the first evidence to show that infants have a repetition bias in learning new words. It also shows that there may be a good reason why in so many cultures across the world, existing adult words and expressions are replaced by words with repeated syllables in baby-talk vocabulary. Some examples could be tum-tum, mama, dada, din-din and wee-wee."