Australian researchers have unlocked the reason why adults use infant directed speech or baby talk when addressing infants.

According to a new study published on Wednesday, the Western Sydney University revealed that mothers unconsciously raise the pitch of their voice as an evolutionary trait in order to comfort their babies and make themselves appear friendlier, Xinua news agency reports.

It also helps babies learn language, as the sounds are clearer and easier to disseminate.

"What we found in this study was that mothers weren't actually making more exaggerated movements with their tongue to make the sound clearer," lead author Dr Marina Kalashnikova said.

"They were shortening the side of the vocal track and that was leading to a higher pitch in their voice and also clearer speech sounds," she added.

The process recorded the sound characteristics of the speech of eight 
mothers when talking to their babies and examined their lips and tongues with equipment that is used in the film industry to create digital effects called electromagnetic articulography (EMA).

Data from the study was then measured against other research which has addressed similar behaviours across many different species, not just humans.

"The size of our vocal tract is characteristic of our body size, that's why women usually have a higher pitch than men," Dr Kalashnikova said.

"You can also think about the sound a mouse makes with a really small vocal tract, compared to the roar of a large lion," she added.

However just like human mothers, animals can modify how they sound in order to comfort their offspring.

"For example, when a large animal approaches their offspring, they can produce a higher pitched vocalization to sound smaller and less threatening," Dr Kalashnikova said.

"But a smaller animal will produce a lower pitch of vocalization to sound bigger and scarier, so their young feel safe."

The lead author said a similar research has concluded that Russian and Swedish languages also use baby talk, adding in the Asian community "when mothers speak in Mandarin, they exaggerate the tone as well as their vowels"