A 2016 study of various English-speaking indigenous North Americans (Slaveys, Standing Rock Lakotas, and diverse Indian students at Dartmouth College) found that they all used uniquely shared prosodic features for occasional emphasis, irony, or playfulness in casual peer interactions, yet rarely in formal interactions. The prosodic choices are presumably a way for these speakers to index (tap into) a shared "Native" identity. The documented sounds of this "Pan-Indian" identity include: higher pitch on post-stressed syllables (rather than stressed syllables); use of high-rising, mid, or high-falling (rather than simple falling) intonation at the ends of sentences; vowel lengthening at the ends of sentences; and syllable timing (instead of stress timing).[9]