In the American South, Black deaf children were long schooled separately, with some schools only desegregating in the 1970s. Cut off from white schools, they developed their own variety: Black American Sign Language (Black ASL). A 2011 study published by Gallaudet University Press documented its features: signs made in a larger space, more two-handed signs, and expressions of its own.
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.