Myself, Connor Mayer, and Bryan Gick recently published “Uniformity in speech: The economy of reuse and adaptation across contexts” with Glossa. This article compares how Kiwis and North Americans produce flap sequences like “editor” in North America, or “added a” in New Zealand. Kiwis produce these similarly during slow and fast speech, North Americans often have two different methods for slow and fast speech. We show that difference likely stems from the extreme variability built into the “r”s of rhotic dialects of English reaching flaps because of reuse and adaptation of motor “chunks”.

To illustrate our claim: In the image below showing tongue tip frontness for the second vowel in 3-vowel-sequences for words like “editor”, you can see that for faster speech (6-7 syllables/second), there is a jump where the tongue tip is not nearly as fronted, but only for North American English (NAE) vowels, not for New Zealand English (NZE) vowels or NAE rhotic vowels. Here the high variability intrinsic to NAE rhotic (and commonly seen in other contexts) is visible in adjacent NAE non-rhotic vowels, but NZE has no access to rhotic vowels at all, so the non-rhotic vowels do not have a source of such motor control variability, even though such variability would provide mechanical advantage.

The abstract for this article, which explains in more technical but also more accurate terms, can be seen here:

“North American English (NAE) flaps/taps and rhotic vowels have been shown to exhibit extreme variability that can be categorized into subphonemic variants. This variability provides known mechanical benefits in NAE speech production. However, we also know languages reuse gestures for maximum efficiency during speech production; this uniformity of behavior reduces gestural variability. Here we test two conflicting hypotheses: Under a uniformity hypothesis in which extreme variability is inherent to rhotic vowels only, that variability can still transfer to flaps/taps and non-rhotic vowels due to adaptation across similar speech contexts. But because of the underlying reliance on extreme variability from rhotic vowels, this uniformity hypothesis does not predict extreme variability in flaps/taps within non-rhotic English dialects. Under a mechanical hypothesis in which extreme variability is inherent to all segments where it would provide mechanical advantage, including flaps/taps, such variability would appear across all English dialects with flaps/taps, affecting adjacent non-rhotic vowels through coarticulation whenever doing so would provide mechanical advantage. We test these two hypotheses by comparing speech-rate-varying NAE sequences with and without rhotic vowels to sequences from New Zealand English (NZE), which has flaps/taps, but no rhotic vowels at all. We find that NZE speakers all use similar tongue-tip motion patterns for flaps/taps across both slow and fast speech, unlike NAE speakers who sometimes use two different stable patterns, one for slow and another fast speech. Results show extreme variability is not inherent to flaps/taps across English dialects, supporting the uniformity hypothesis.”