At 6 to 8 months, English-learning babies easily tell apart two Hindi 't' sounds that their parents can't distinguish. By 10 to 12 months, most have lost that ability: their brains have specialised in the sounds of the language around them. Babies start out as 'citizens of the world' and then become specialists.
In Kuşköy, a mountain village in northern Turkey, people talk across valleys by whistling Turkish. A 2015 study showed that whistled Turkish draws on both hemispheres fairly evenly, whereas spoken Turkish relies mostly on the left. The physical form of the signal, it turns out, matters to the brain.
Speech has no gaps between words. In 1996, researchers played 8-month-old babies a continuous stream of made-up syllables for just two minutes. The infants picked out the 'words' by tracking which syllables tend to follow one another. That's probability calculation, done without a calculator or any visible effort.