In deaf signers, damage to the left hemisphere can cause sign-language aphasia: distorted signs and broken grammar, just like a hearing person losing speech. Right-hemisphere damage usually leaves the language intact, even though signing relies heavily on space. As far as the brain is concerned, signing is speaking a language.
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.